[{"text": "[SQUEAKING][RUSTLING][CLICKING]", "start": 0.0, "duration": 2.42}, {"text": "MATTHEW VANDER\nHEIDEN: Last time, we", "start": 9.68, "duration": 1.88}, {"text": "discussed oxidative\nphosphorylation, which", "start": 11.56, "duration": 3.66}, {"text": "is how to couple the NADH\ngenerated from sugar,", "start": 15.22, "duration": 5.49}, {"text": "fatty acids, et cetera; the\noxidation of carbon as a way", "start": 20.71, "duration": 4.68}, {"text": "to carry out favorable\nelectron transfer to oxygen", "start": 25.39, "duration": 3.81}, {"text": "and use that energy release\nto charge a battery--", "start": 29.2, "duration": 3.45}, {"text": "that is, create\nthis delta psi/delta", "start": 32.65, "duration": 3.24}, {"text": "pH that can subsequently be\nused by the battery to do work,", "start": 35.89, "duration": 5.47}, {"text": "including the synthesis of ADP.", "start": 41.36, "duration": 2.87}, {"text": "And of course, this can occur\nat a physiological ATP/ADP ratio", "start": 44.23, "duration": 4.41}, {"text": "and, therefore, allow\nthe cell to couple ATP", "start": 48.64, "duration": 2.98}, {"text": "to ADP conversion to other\nunfavorable processes", "start": 51.62, "duration": 2.6}, {"text": "in the cell.", "start": 54.22, "duration": 1.54}, {"text": "Now, all of these reactions\noccur at the mitochondria.", "start": 55.76, "duration": 2.69}, {"text": "And I drew, here, a\nschematic mitochondria for us", "start": 58.45, "duration": 3.06}, {"text": "just to start.", "start": 61.51, "duration": 1.06}, {"text": "Remember, the mitochondria\nhas its own genome.", "start": 62.57, "duration": 3.72}, {"text": "This is a vestige of the\nsymbiotic relationship that", "start": 66.29, "duration": 3.89}, {"text": "developed long, long ago, where\ntwo prokaryotes came together,", "start": 70.18, "duration": 5.4}, {"text": "leading to this symbiotic\nrelationship-- but of course,", "start": 75.58, "duration": 5.14}, {"text": "the mitochondrial\nDNA encoding many", "start": 80.72, "duration": 2.45}, {"text": "of the key components of\nthis electron transport chain", "start": 83.17, "duration": 4.14}, {"text": "and ATP synthesis machinery\nthat remains in the mitochondria", "start": 87.31, "duration": 4.17}, {"text": "today.", "start": 91.48, "duration": 1.05}, {"text": "Now, ultimately, this process\ninvolves the reoxidation", "start": 92.53, "duration": 3.84}, {"text": "of NADH back to NAD that occurs,\nthat complex I of the electron", "start": 96.37, "duration": 6.69}, {"text": "transport chain.", "start": 103.06, "duration": 1.35}, {"text": "Those electrons are transferred\ninto the Q pool, which", "start": 104.41, "duration": 2.82}, {"text": "then go into complex III to\ncytochrome c to complex IV,", "start": 107.23, "duration": 3.93}, {"text": "ultimately being transferred\nto oxygen as the final electron", "start": 111.16, "duration": 5.97}, {"text": "acceptor.", "start": 117.13, "duration": 0.72}, {"text": "And it's this process of\nfavorable electron transport--", "start": 117.85, "duration": 3.45}, {"text": "that is, electrons\nmoving from a lower", "start": 121.3, "duration": 2.37}, {"text": "to a higher standard\nreduction potential-- that", "start": 123.67, "duration": 2.52}, {"text": "is coupled to the\npumping of protons", "start": 126.19, "duration": 2.19}, {"text": "and the generation of\nthis delta psi/delta pH.", "start": 128.38, "duration": 3.45}, {"text": "Now, we also discussed complex\nII of the electron transport", "start": 131.83, "duration": 3.63}, {"text": "chain, which is identical\nto succinate dehydrogenase", "start": 135.46, "duration": 3.66}, {"text": "in the TCA cycle.", "start": 139.12, "duration": 1.38}, {"text": "This is involving that\nFAD/FADH2, which can, itself,", "start": 140.5, "duration": 5.52}, {"text": "also transfer electrons\nto the Q pool,", "start": 146.02, "duration": 2.58}, {"text": "ultimately passing\nthose to complex III", "start": 148.6, "duration": 2.34}, {"text": "to cytochrome c to\ncomplex IV, again,", "start": 150.94, "duration": 2.91}, {"text": "with oxygen as\nelectron acceptor,", "start": 153.85, "duration": 2.88}, {"text": "ultimately forming\nwhat is essentially", "start": 156.73, "duration": 2.7}, {"text": "two different variations\non the electron transport", "start": 159.43, "duration": 3.87}, {"text": "chain as a way to generate\ndelta psi/delta pH.", "start": 163.3, "duration": 4.17}, {"text": "Now I show here, on the\nslide, that there's really", "start": 167.47, "duration": 4.62}, {"text": "many versions of this\nelectron transport chain,", "start": 172.09, "duration": 2.94}, {"text": "and another one we discussed\nis shown down here.", "start": 175.03, "duration": 2.44}, {"text": "So up here is the typical one to\nregenerate NAD+ using complex I", "start": 177.47, "duration": 5.75}, {"text": "to the Q pool to III to c to IV.", "start": 183.22, "duration": 2.55}, {"text": "Here's the one involving complex\nII, so dehydrogenase reaction", "start": 185.77, "duration": 5.22}, {"text": "via complex II to the Q\npool, complex III, c, IV.", "start": 190.99, "duration": 4.59}, {"text": "And then there's yet a third one\nhere from fatty acid oxidation.", "start": 195.58, "duration": 3.67}, {"text": "So this is Acyl-CoA\ndehydrogenase.", "start": 199.25, "duration": 2.63}, {"text": "Again, like complex\nII, involves FAD/FADH2.", "start": 201.88, "duration": 4.08}, {"text": "This occurs at the\nmembrane, transfers", "start": 205.96, "duration": 2.91}, {"text": "electrons to the Q\npool to III to c to IV,", "start": 208.87, "duration": 3.12}, {"text": "ultimately reducing\noxygen to water.", "start": 211.99, "duration": 3.16}, {"text": "And so the net effect of\nthese various electron", "start": 215.15, "duration": 3.77}, {"text": "transport chains\nwere shown up here", "start": 218.92, "duration": 2.61}, {"text": "is generating this delta\npsi/delta pH, which", "start": 221.53, "duration": 4.14}, {"text": "can then be used to do work.", "start": 225.67, "duration": 2.47}, {"text": "Now, the cool thing\nis is that this", "start": 228.14, "duration": 2.9}, {"text": "is occurring, in this case,\nat the inner mitochondrial", "start": 231.04, "duration": 2.37}, {"text": "membrane.", "start": 233.41, "duration": 0.82}, {"text": "And so you can do work in\nlots of different ways.", "start": 234.23, "duration": 2.66}, {"text": "It doesn't have to be\nnext to the complex.", "start": 236.89, "duration": 1.75}, {"text": "You have a charge\nacross the membrane that", "start": 238.64, "duration": 1.97}, {"text": "can be used different\nplaces in space,", "start": 240.61, "duration": 2.05}, {"text": "such as so-called complex\nV or the F1F0-ATPase,", "start": 242.66, "duration": 4.19}, {"text": "which can use dissipation\nof that proton gradient", "start": 246.85, "duration": 3.48}, {"text": "to drive that rotational\ncatalysis machine we described", "start": 250.33, "duration": 3.66}, {"text": "last time and, ultimately,\ntake ADP plus phosphate", "start": 253.99, "duration": 3.15}, {"text": "and synthesize ATP.", "start": 257.14, "duration": 2.31}, {"text": "But that's not the\nonly work it can do.", "start": 259.45, "duration": 1.65}, {"text": "You can uncouple\nthe whole thing.", "start": 261.1, "duration": 2.13}, {"text": "We discussed these\nuncoupling proteins,", "start": 263.23, "duration": 2.31}, {"text": "which, effectively,\njust let protons leak", "start": 265.54, "duration": 2.58}, {"text": "back across into the membranes,\nthat short-circuiting", "start": 268.12, "duration": 3.45}, {"text": "this potential.", "start": 271.57, "duration": 1.14}, {"text": "And that's a way\nto generate heat.", "start": 272.71, "duration": 2.61}, {"text": "Other type of work\nwe can do is we", "start": 275.32, "duration": 1.86}, {"text": "can use this proton\ngradient to power", "start": 277.18, "duration": 4.02}, {"text": "the transport of other ions.", "start": 281.2, "duration": 2.67}, {"text": "We discussed this happening\nwith ADP/ATP exchange", "start": 283.87, "duration": 3.96}, {"text": "because, of course,\nADP-to-ATP conversion", "start": 287.83, "duration": 2.64}, {"text": "needed in the cytosol to favor\nunfavorable processes there.", "start": 290.47, "duration": 3.36}, {"text": "Need to exchange those in\nand out of the mitochondria,", "start": 293.83, "duration": 2.29}, {"text": "so you can regenerate ATP with\nthe ATP synthase machinery.", "start": 296.12, "duration": 3.83}, {"text": "And yet another thing\nwe talked about is", "start": 299.95, "duration": 1.68}, {"text": "you can use this as a\nway to concentrate ions,", "start": 301.63, "duration": 2.05}, {"text": "such as calcium.", "start": 303.68, "duration": 1.43}, {"text": "And the mitochondria ends\nup being a major calcium", "start": 305.11, "duration": 2.73}, {"text": "store for cells.", "start": 307.84, "duration": 3.02}, {"text": "Now, we discussed last time\nthat this is great having all", "start": 310.86, "duration": 8.31}, {"text": "of these oxidation\nprocesses-- the TCA cycle,", "start": 319.17, "duration": 2.7}, {"text": "fatty acid oxidation--", "start": 321.87, "duration": 1.62}, {"text": "all occurring in the\nmatrix because it", "start": 323.49, "duration": 1.74}, {"text": "gives a location for\nNAD/NADH to happen where", "start": 325.23, "duration": 4.95}, {"text": "it has easy access to this\nelectron transport machinery", "start": 330.18, "duration": 4.41}, {"text": "and the ability to regenerate\nthe NAD necessary to keep these", "start": 334.59, "duration": 3.96}, {"text": "processes going.", "start": 338.55, "duration": 1.63}, {"text": "But of course, the very first\nprocess we talked about happens", "start": 340.18, "duration": 2.87}, {"text": "in the cytosol, and\nthat's glycolysis.", "start": 343.05, "duration": 2.88}, {"text": "And we discussed how\nyou can bring pyruvate", "start": 345.93, "duration": 2.31}, {"text": "into the mitochondria through\nthis mitochondrial pyruvate", "start": 348.24, "duration": 2.56}, {"text": "carrier.", "start": 350.8, "duration": 1.04}, {"text": "Then it has access to the\npyruvate dehydrogenase", "start": 351.84, "duration": 2.82}, {"text": "reaction, which, of course,\ngenerates acetyl-CoA", "start": 354.66, "duration": 3.14}, {"text": "and NADH in the right place.", "start": 357.8, "duration": 2.51}, {"text": "However, if you go way back to\nwhen we discuss fermentation,", "start": 360.31, "duration": 3.05}, {"text": "remember, the reason we had to\nsend pyruvate to fermentation", "start": 363.36, "duration": 3.66}, {"text": "was to regenerate that\nNAD in the cytosol that's", "start": 367.02, "duration": 4.11}, {"text": "necessary to keep\nglycolysis going.", "start": 371.13, "duration": 3.1}, {"text": "Now, of course, if we're\ngoing to fully oxidize", "start": 374.23, "duration": 3.68}, {"text": "pyruvate carbon in\nthe mitochondria,", "start": 377.91, "duration": 2.31}, {"text": "we still have to solve\nthis electron balance", "start": 380.22, "duration": 3.12}, {"text": "problem for glycolysis.", "start": 383.34, "duration": 2.16}, {"text": "And as we discussed,\nwe can solve that", "start": 385.5, "duration": 2.16}, {"text": "by giving those\nelectrons to oxygen.", "start": 387.66, "duration": 2.13}, {"text": "But now you see that there's\nthis additional complication--", "start": 389.79, "duration": 3.21}, {"text": "is that these electrons\nin the form of NADH", "start": 393.0, "duration": 3.48}, {"text": "need to get inside the\nmitochondrial matrix", "start": 396.48, "duration": 2.94}, {"text": "or get to the electron\ntransport chain", "start": 399.42, "duration": 2.64}, {"text": "as a way to use oxygen\nto ultimately dispose", "start": 402.06, "duration": 4.68}, {"text": "of those electrons.", "start": 406.74, "duration": 1.06}, {"text": "And so, effectively,\nthat NADH needs", "start": 407.8, "duration": 2.6}, {"text": "to be gotten to\ncomplex I, which would", "start": 410.4, "duration": 3.03}, {"text": "be the matrix in the\nway we've drawn it here.", "start": 413.43, "duration": 4.47}, {"text": "Now, really, the way that\nthis happens is not direct.", "start": 417.9, "duration": 6.55}, {"text": "So you don't transport\nNADH from the cytosol", "start": 424.45, "duration": 4.8}, {"text": "into the mitochondria.", "start": 429.25, "duration": 2.34}, {"text": "And that's partially because\none of the benefits, remember,", "start": 431.59, "duration": 4.32}, {"text": "of having compartmentalized\nmetabolism", "start": 435.91, "duration": 2.55}, {"text": "is your ability to have\ndifferent conditions;", "start": 438.46, "duration": 2.8}, {"text": "different ATP/ADP\nratios, NAD/NADH ratios", "start": 441.26, "duration": 3.207}, {"text": "in different\ncompartments because that", "start": 444.467, "duration": 1.583}, {"text": "can favor different chemistry.", "start": 446.05, "duration": 2.02}, {"text": "And so the way that you get\nelectrons into the matrix", "start": 448.07, "duration": 5.78}, {"text": "or get electrons to the\nelectron transport chains", "start": 453.85, "duration": 3.0}, {"text": "doesn't occur directly.", "start": 456.85, "duration": 1.41}, {"text": "You do not transport\nNAD or NADH directly.", "start": 458.26, "duration": 4.11}, {"text": "Instead, you use\nso-called shuttles,", "start": 462.37, "duration": 4.85}, {"text": "which are analogous to some\nof the other shuttles we've", "start": 467.22, "duration": 3.27}, {"text": "talked about, in order to get\nmaterials across membranes.", "start": 470.49, "duration": 3.15}, {"text": "In this case, this\nis a way to get", "start": 473.64, "duration": 1.83}, {"text": "electrons generated\nfrom oxidation", "start": 475.47, "duration": 2.88}, {"text": "reactions in the cytosol--", "start": 478.35, "duration": 1.74}, {"text": "production of NADH in\nthe cytosol, things", "start": 480.09, "duration": 2.31}, {"text": "like glycolysis--", "start": 482.4, "duration": 2.64}, {"text": "to the electron transport chain\nso that they can ultimately", "start": 485.04, "duration": 3.48}, {"text": "be transferred to oxygen.", "start": 488.52, "duration": 3.6}, {"text": "And so these shuttles,\nor redox shuttles,", "start": 492.12, "duration": 8.18}, {"text": "actually come in\nseveral different ways", "start": 500.3, "duration": 3.24}, {"text": "that cells can deal with\ncytosolic electrons.", "start": 503.54, "duration": 4.36}, {"text": "And so these shuttles\nalso, in essence,", "start": 507.9, "duration": 6.33}, {"text": "help cells also establish\nthese different conditions,", "start": 514.23, "duration": 4.62}, {"text": "these different NAD/NADH ratios\nin different compartments.", "start": 518.85, "duration": 3.71}, {"text": "And so you can imagine that the\nshuttles themselves could be", "start": 522.56, "duration": 2.5}, {"text": "regulated as a way to do this.", "start": 525.06, "duration": 2.64}, {"text": "Now, there's two\nmajor redox shuttles", "start": 527.7, "duration": 3.0}, {"text": "that allow you to move\nelectrons from the cytosol", "start": 530.7, "duration": 3.69}, {"text": "into the mitochondria, and we'll\ndiscuss those two here next.", "start": 534.39, "duration": 7.08}, {"text": "These are the two\nthat probably are", "start": 541.47, "duration": 2.1}, {"text": "being looked for if you get\nthis question on an MCAT exam", "start": 543.57, "duration": 5.13}, {"text": "or something like that.", "start": 548.7, "duration": 1.602}, {"text": "They're the ones\nthat are described", "start": 550.302, "duration": 1.458}, {"text": "in the text as the way to\nget electrons to the electron", "start": 551.76, "duration": 3.33}, {"text": "transport chain.", "start": 555.09, "duration": 1.29}, {"text": "But however, as we\ngo through them,", "start": 556.38, "duration": 2.53}, {"text": "you will see that there's\na couple different ways", "start": 558.91, "duration": 2.82}, {"text": "one can do this.", "start": 561.73, "duration": 0.74}, {"text": "They basically involve\noxidation and reduction", "start": 562.47, "duration": 3.24}, {"text": "of a pair of molecules on\neither side of the membrane.", "start": 565.71, "duration": 3.96}, {"text": "And there's lots of ways\nyou can do that in addition", "start": 569.67, "duration": 2.49}, {"text": "to these other shuttles.", "start": 572.16, "duration": 2.13}, {"text": "It'll become more clear\nwhat I mean by this,", "start": 574.29, "duration": 1.95}, {"text": "but I guess I just want you\nto know that these are not", "start": 576.24, "duration": 2.79}, {"text": "the only ways one\ncould shuttle electrons", "start": 579.03, "duration": 2.79}, {"text": "into the mitochondria.", "start": 581.82, "duration": 1.44}, {"text": "These are just the major\nways that have been discussed", "start": 583.26, "duration": 5.19}, {"text": "and are usually\ndiscussed in textbooks.", "start": 588.45, "duration": 4.18}, {"text": "So the first shuttle\nsystem is something called", "start": 592.63, "duration": 4.37}, {"text": "the glycerol phosphate shuttle.", "start": 597.0, "duration": 5.865}, {"text": "And so the glycerol\nphosphate shuttle", "start": 605.49, "duration": 3.42}, {"text": "involves a reaction that\nwe've already discussed.", "start": 608.91, "duration": 4.17}, {"text": "So here's our old friend,\ndihyroxyacetone phosphate", "start": 622.75, "duration": 3.86}, {"text": "from glycolysis.", "start": 626.61, "duration": 2.31}, {"text": "Remember when we talked\nabout the generation of", "start": 628.92, "duration": 3.93}, {"text": "and metabolism of\nglycerol, in order", "start": 632.85, "duration": 1.92}, {"text": "to make triacylglycerides,\nphospholipids--", "start": 634.77, "duration": 2.76}, {"text": "remember we described\nthat you can", "start": 637.53, "duration": 2.61}, {"text": "take dihyroxyacetone phosphate.", "start": 640.14, "duration": 2.19}, {"text": "If you use NADH to reduce\nthat ketone to the alcohol,", "start": 646.54, "duration": 15.72}, {"text": "that generates this\nmolecule, glycerol phosphate.", "start": 662.26, "duration": 5.32}, {"text": "And of course, because\nyou're reducing the ketone", "start": 667.58, "duration": 2.55}, {"text": "to the alcohol, something\nelse has to be oxidized.", "start": 670.13, "duration": 2.34}, {"text": "You reoxidized\nNADH back to NAD+,", "start": 672.47, "duration": 3.96}, {"text": "effectively disposing of\nthose electrons from, say,", "start": 676.43, "duration": 5.18}, {"text": "glycolysis that generated\nNADH to regenerate NAD+.", "start": 681.61, "duration": 6.54}, {"text": "Now, rather than use this\nglycerol phosphate and lipid", "start": 688.15, "duration": 2.73}, {"text": "synthesis, turns out\nthere's a complex that", "start": 690.88, "duration": 3.21}, {"text": "can directly transfer\nthose electrons to FAD", "start": 694.09, "duration": 10.85}, {"text": "to generate FADH2.", "start": 704.94, "duration": 4.8}, {"text": "And this complex sits within the\ninner mitochondrial membrane,", "start": 709.74, "duration": 7.01}, {"text": "facing the cytosolic\nside of the membrane.", "start": 716.75, "duration": 4.29}, {"text": "Here's the inner\nmitochondrial membrane.", "start": 724.232, "duration": 2.028}, {"text": "This would be the matrix.", "start": 726.26, "duration": 2.91}, {"text": "And so transferring\nthose electrons", "start": 729.17, "duration": 2.75}, {"text": "to FAD to reduce\nto FADH2 reoxidizes", "start": 731.92, "duration": 5.17}, {"text": "the glycerol phosphate back\nto dihydroxyacetone phosphate.", "start": 737.09, "duration": 3.83}, {"text": "And of course, in this membrane,\nyou can, in this complex,", "start": 740.92, "duration": 3.6}, {"text": "transfer those electrons\nby oxidizing the FAD", "start": 744.52, "duration": 3.96}, {"text": "and sending them to\nthe coenzyme Q pool.", "start": 748.48, "duration": 4.59}, {"text": "That can take the\nubiquinone, makes ubinquinol.", "start": 753.07, "duration": 3.3}, {"text": "Those electrons can\ngo to complex III.", "start": 756.37, "duration": 2.04}, {"text": "That can go to cytochrome C.\nThey can go to complex IV,", "start": 758.41, "duration": 4.38}, {"text": "ultimately ending up reducing\noxygen to water using oxygen", "start": 762.79, "duration": 8.28}, {"text": "as a final electron acceptor.", "start": 771.07, "duration": 2.19}, {"text": "Again, this is effectively\nanother alternative", "start": 773.26, "duration": 5.07}, {"text": "to the electron transport chain.", "start": 778.33, "duration": 2.29}, {"text": "And so I show that\nhere on the slide.", "start": 780.62, "duration": 1.72}, {"text": "And so we've discussed--", "start": 782.34, "duration": 1.29}, {"text": "the complex II-- this is the\nFAD/FADH2 containing enzyme", "start": 788.83, "duration": 4.92}, {"text": "is complex II.", "start": 793.75, "duration": 1.03}, {"text": "Succinate dehydrogenase sits\nin the inner mitochondrial", "start": 794.78, "duration": 3.41}, {"text": "membrane, converts\nsuccinate to fumarate.", "start": 798.19, "duration": 2.97}, {"text": "Those electrons\nend up on up FADH2,", "start": 801.16, "duration": 3.12}, {"text": "can get transferred\nto the Q pool,", "start": 804.28, "duration": 1.445}, {"text": "reoxidizing FAD to complex III\nto cytochrome C to complex IV", "start": 805.725, "duration": 5.695}, {"text": "to oxygen to water.", "start": 811.42, "duration": 2.61}, {"text": "We already discussed acyl-CoA\ndehydrogenase-- same thing.", "start": 814.03, "duration": 3.51}, {"text": "FADH2 containing reaction in\nthere is also in the membrane--", "start": 817.54, "duration": 3.75}, {"text": "ultimately allows another\nversion electron transport", "start": 821.29, "duration": 2.91}, {"text": "chain.", "start": 824.2, "duration": 0.78}, {"text": "And here's yet a third one\ninvolving an FDA using enzyme.", "start": 824.98, "duration": 4.26}, {"text": "The difference is is that these\nhave the oxidation reduction", "start": 829.24, "duration": 4.62}, {"text": "reaction occurring\non the matrix side--", "start": 833.86, "duration": 2.25}, {"text": "succinate to fumarate\non the matrix side--", "start": 836.11, "duration": 2.79}, {"text": "the introduction\nof a double bond", "start": 838.9, "duration": 2.19}, {"text": "for fatty acid oxidation\nand the matrix side.", "start": 841.09, "duration": 2.52}, {"text": "This one here instead\nfaces the cytosolic side.", "start": 843.61, "duration": 3.51}, {"text": "So glycerol 3 phosphate\ncan be reoxidized", "start": 847.12, "duration": 5.01}, {"text": "to dihydroxyacetone phosphate--", "start": 852.13, "duration": 5.09}, {"text": "looks like I have those arrows\ndrawn backwards, sorry--", "start": 857.22, "duration": 2.75}, {"text": "ultimately sending electrons\ninto this glycerol phosphate", "start": 859.97, "duration": 5.04}, {"text": "shuttle, reducing FADH2,\nwhich can be reoxidized", "start": 865.01, "duration": 4.88}, {"text": "by giving those electrons to\nthe Q pool to complex III,", "start": 869.89, "duration": 3.28}, {"text": "to cytochrome C, to\ncomplex IV, ultimately", "start": 873.17, "duration": 3.23}, {"text": "with water serving as the\nfinal electron acceptor,", "start": 876.4, "duration": 4.5}, {"text": "as I've drawn here.", "start": 880.9, "duration": 2.56}, {"text": "Now, if you notice, if\nwe use this system or any", "start": 883.46, "duration": 5.52}, {"text": "of these systems, these\nalternative FAD/FADH2 using", "start": 888.98, "duration": 5.7}, {"text": "electron transport chains,\nyou don't use complex I.", "start": 894.68, "duration": 4.71}, {"text": "Remember, complex I will pump\na proton, complex II will not.", "start": 899.39, "duration": 5.86}, {"text": "And that means that if you\nuse any of these FADH2 using", "start": 905.25, "duration": 4.88}, {"text": "alternative electron\ntransport chains,", "start": 910.13, "duration": 2.25}, {"text": "you pump fewer protons\ninto the cytosol.", "start": 912.38, "duration": 3.36}, {"text": "And so if you donate the\nelectrons to complex I", "start": 915.74, "duration": 3.84}, {"text": "from the matrix,\nyou pump a proton", "start": 919.58, "duration": 2.7}, {"text": "as you go through\ncomplex I to the Q pool", "start": 922.28, "duration": 2.61}, {"text": "if you go through the\nglycerol phosphate shuttle,", "start": 924.89, "duration": 2.73}, {"text": "you avoid complex I, because you\ngive those electrons directly", "start": 927.62, "duration": 3.93}, {"text": "to the glycerol\nphosphate shuttle.", "start": 931.55, "duration": 1.83}, {"text": "And FAD/FADH2 enzyme--\nthose end up in the Q pool.", "start": 933.38, "duration": 3.51}, {"text": "Less protons are pumped.", "start": 936.89, "duration": 2.07}, {"text": "And this is why sometimes\nin textbooks, you'll", "start": 938.96, "duration": 2.58}, {"text": "see that you get less ATP per\nNADH produced in the cytosol", "start": 941.54, "duration": 4.53}, {"text": "than you get for NADH\nproduced in the mitochondria.", "start": 946.07, "duration": 5.35}, {"text": "And this is one of the\nways that you end up", "start": 951.42, "duration": 3.86}, {"text": "with these accounting yields for\nglucose oxidation-- something", "start": 955.28, "duration": 4.2}, {"text": "we'll talk about in a minute.", "start": 959.48, "duration": 2.95}, {"text": "But the deeper reason for this,\nwhich I want you to appreciate,", "start": 962.43, "duration": 2.96}, {"text": "is because FADH2 has a higher\nstandard reduction potential.", "start": 965.39, "duration": 6.79}, {"text": "So the standard reduction\npotential of FAD/FADH2", "start": 972.18, "duration": 8.03}, {"text": "is greater than it\nis for NAD/NADH.", "start": 980.21, "duration": 4.035}, {"text": "In essence, that\nmeans that there's", "start": 987.7, "duration": 2.37}, {"text": "less change in\nstandard reduction", "start": 990.07, "duration": 1.71}, {"text": "potential for transferring FADH2\nelectrons to oxygen as there is", "start": 991.78, "duration": 6.0}, {"text": "for transferring\nelectrons to oxygen.", "start": 997.78, "duration": 3.51}, {"text": "And so less energy released,\nless protons pumped,", "start": 1001.29, "duration": 3.66}, {"text": "and so that's why you get\nless ATP, if you will,", "start": 1004.95, "duration": 4.65}, {"text": "produced going through the\nglycerol phosphate shuttle.", "start": 1009.6, "duration": 5.0}, {"text": "All right.", "start": 1014.6, "duration": 1.85}, {"text": "Next, I want to discuss\nanother alternative shuttle", "start": 1016.45, "duration": 4.92}, {"text": "to get electrons into\nthe mitochondria.", "start": 1021.37, "duration": 2.56}, {"text": "And this involves much more\nwhat I was alluding to earlier.", "start": 1023.93, "duration": 3.38}, {"text": "And that's oxidation\nand reduction", "start": 1027.31, "duration": 2.19}, {"text": "of a pair of metabolites\nthat are transported", "start": 1029.5, "duration": 3.545}, {"text": "across the membrane on\neither side of the membrane,", "start": 1033.045, "duration": 2.125}, {"text": "effectively moving electrons\nfrom one compartment", "start": 1035.17, "duration": 4.32}, {"text": "in the cell to another.", "start": 1039.49, "duration": 1.9}, {"text": "Now, to understand how this\nshuttle works, I have to--", "start": 1041.39, "duration": 4.365}, {"text": "because it's a little\nmore complicated,", "start": 1045.755, "duration": 1.625}, {"text": "I have to first\ndescribe that there's", "start": 1047.38, "duration": 2.37}, {"text": "a relationship between amino\nacids and alpha-keto acids.", "start": 1049.75, "duration": 5.08}, {"text": "And so, what do I mean by that?", "start": 1054.83, "duration": 1.41}, {"text": "Well, here's a alpha-keto acid\nthat we've talked about a lot.", "start": 1056.24, "duration": 7.91}, {"text": "So this is oxaloacetate.", "start": 1064.15, "duration": 3.45}, {"text": "Remember, it's an alpha\nketo-acid because this ketone", "start": 1067.6, "duration": 3.45}, {"text": "is alpha to this\ncarboxylic acid--", "start": 1071.05, "duration": 5.11}, {"text": "so an alpha-keto acid.", "start": 1076.16, "duration": 2.7}, {"text": "Turns out that\nalpha-keto acids are", "start": 1078.86, "duration": 4.34}, {"text": "related to amino acids\nin the following way.", "start": 1083.2, "duration": 6.73}, {"text": "And so if I take\nthat alpha-keto group", "start": 1089.93, "duration": 3.62}, {"text": "and instead make\nit an amino group,", "start": 1093.55, "duration": 6.23}, {"text": "this here is the\namino acid aspartame.", "start": 1099.78, "duration": 3.81}, {"text": "Now, we'll discuss\nlater in the course", "start": 1109.03, "duration": 2.41}, {"text": "the chemistry that allows\nyou to interconvert", "start": 1111.44, "duration": 2.27}, {"text": "this alpha-keto group\nwith this amino group.", "start": 1113.71, "duration": 2.94}, {"text": "But that's effectively where\nyour amino acids come from--", "start": 1116.65, "duration": 4.05}, {"text": "how your amino acids are related\nto other aspects of carbon", "start": 1120.7, "duration": 5.43}, {"text": "metabolism--", "start": 1126.13, "duration": 0.78}, {"text": "Alpha-keto acids that are\ngenerated in metabolism.", "start": 1126.91, "duration": 3.18}, {"text": "And so there's one example--", "start": 1130.09, "duration": 2.82}, {"text": "oxaloacetate and aspartate, an\nalpha-keto acid, an amino acid.", "start": 1132.91, "duration": 6.4}, {"text": "Here's another one.", "start": 1139.31, "duration": 0.905}, {"text": "So this is alpha-ketoglutarate--", "start": 1149.29, "duration": 2.43}, {"text": "an alpha-keto acid.", "start": 1156.51, "duration": 2.8}, {"text": "And if we change that alpha\ngroup to an amino group,", "start": 1159.31, "duration": 11.46}, {"text": "now we get the amino\nacid glutamate.", "start": 1170.77, "duration": 8.42}, {"text": "All right.", "start": 1179.19, "duration": 0.93}, {"text": "To remind you, the three letter\nabbreviation for aspartate", "start": 1180.12, "duration": 4.26}, {"text": "is a-s-p.", "start": 1184.38, "duration": 1.02}, {"text": "The one letter is D. The\nthree letter abbreviation", "start": 1185.4, "duration": 4.18}, {"text": "for glutamate is g-l-u.", "start": 1189.58, "duration": 3.9}, {"text": "And the one letter\nabbreviation is E.", "start": 1193.48, "duration": 2.79}, {"text": "And I just remind you of that in\ncase I use those abbreviations.", "start": 1196.27, "duration": 4.62}, {"text": "But effectively, you can note\nthat if you couple these swaps", "start": 1200.89, "duration": 5.31}, {"text": "to each other--", "start": 1206.2, "duration": 0.99}, {"text": "that is, if I take\noxaloacetate and turn it", "start": 1207.19, "duration": 4.26}, {"text": "into aspartate while at the\nsame time taking glutamate", "start": 1211.45, "duration": 8.17}, {"text": "and turning it into\nalpha-ketoglutarate,", "start": 1219.62, "duration": 3.66}, {"text": "you can see that that\nis a reaction where", "start": 1223.28, "duration": 4.35}, {"text": "all atoms are conserved.", "start": 1227.63, "duration": 2.07}, {"text": "That is, if I turn this amino\nacid into this alpha-keto acid", "start": 1229.7, "duration": 6.27}, {"text": "while at the same time\nturning that alpha-keto acid", "start": 1235.97, "duration": 2.28}, {"text": "into this amino acid, I have\nnot gained or lost any atoms", "start": 1238.25, "duration": 5.43}, {"text": "or molecules in the process.", "start": 1243.68, "duration": 3.03}, {"text": "And we will see\nlater in the course", "start": 1246.71, "duration": 2.07}, {"text": "that these types\nof interconversions", "start": 1248.78, "duration": 2.07}, {"text": "is exactly how you run\nthese reactions to do", "start": 1250.85, "duration": 6.24}, {"text": "these interconversions\nbetween alpha-keto acids", "start": 1257.09, "duration": 2.22}, {"text": "and amino acids.", "start": 1259.31, "duration": 2.67}, {"text": "OK.", "start": 1261.98, "duration": 0.93}, {"text": "Why am I telling you this now?", "start": 1262.91, "duration": 1.5}, {"text": "Because it turns out this\nis central to understand", "start": 1264.41, "duration": 2.79}, {"text": "the other major shuttle,\nwhich is referred", "start": 1267.2, "duration": 4.65}, {"text": "to as the malate-aspartate\nshuttle as another way", "start": 1271.85, "duration": 10.65}, {"text": "to get electrons and\nNADH from the cytosol", "start": 1282.5, "duration": 4.23}, {"text": "into the mitochondria.", "start": 1286.73, "duration": 2.57}, {"text": "All right.", "start": 1289.3, "duration": 0.5}, {"text": "So how does this happen?", "start": 1289.8, "duration": 1.57}, {"text": "So here if you have--", "start": 1291.37, "duration": 3.69}, {"text": "here's oxaloacetate.", "start": 1300.77, "duration": 2.49}, {"text": "This is occurring up\nhere in the cytosol.", "start": 1303.26, "duration": 5.01}, {"text": "OK.", "start": 1308.27, "duration": 1.05}, {"text": "And if we take oxaloacetate\nin the cytosol and we", "start": 1309.32, "duration": 5.82}, {"text": "utilize the malate\ndehydrogenase reaction", "start": 1315.14, "duration": 6.35}, {"text": "that we heard about\nfrom the TCA cycle--", "start": 1321.49, "duration": 2.265}, {"text": "so basically this is the reverse\nof the malate dehydrogenase", "start": 1332.08, "duration": 3.51}, {"text": "reaction we discussed\nin the TCA cycle.", "start": 1335.59, "duration": 2.37}, {"text": "We're going to reduce this\nketone to the alcohol.", "start": 1337.96, "duration": 3.51}, {"text": "NADH is reoxidized to NAD+.", "start": 1341.47, "duration": 3.96}, {"text": "That will generate malate.", "start": 1345.43, "duration": 13.52}, {"text": "And now we've regenerated NAD+\nin the cytosol by putting those", "start": 1358.95, "duration": 6.87}, {"text": "electrons onto oxaloacetate\nto make malate.", "start": 1365.82, "duration": 4.785}, {"text": "All right.", "start": 1370.605, "duration": 1.455}, {"text": "Now, we can take\nthat malate, send it", "start": 1372.06, "duration": 5.55}, {"text": "across the mitochondrial\nmembranes via transporter", "start": 1377.61, "duration": 12.75}, {"text": "to generate, on the matrix\nside of the membrane,", "start": 1390.36, "duration": 5.11}, {"text": "malate, whereas\nfrom the TCA cycle,", "start": 1395.47, "duration": 10.15}, {"text": "we also have malate\ndehydrogenase that can now", "start": 1405.62, "duration": 15.3}, {"text": "reoxidize that carbon from\nthe alcohol to the ketone", "start": 1420.92, "duration": 11.86}, {"text": "and regenerate\noxaloacetate effectively", "start": 1432.78, "duration": 5.22}, {"text": "by carrying out the same\nreaction through a redox pair", "start": 1438.0, "duration": 4.32}, {"text": "on two sides of the membrane.", "start": 1442.32, "duration": 1.53}, {"text": "Effectively what\nI've done is I've", "start": 1443.85, "duration": 2.05}, {"text": "moved the electrons\nfrom NADH in the cytosol", "start": 1445.9, "duration": 3.44}, {"text": "to now being NADH in the\nmitochondrial matrix, where", "start": 1449.34, "duration": 4.44}, {"text": "this can now donate the\nelectrons to complex I,", "start": 1453.78, "duration": 2.73}, {"text": "to the Q pool, to complex III,\nto cytochrome C, to complex IV,", "start": 1456.51, "duration": 4.95}, {"text": "and ultimately to\noxygen, just like it", "start": 1461.46, "duration": 3.84}, {"text": "would for the TCA cycle.", "start": 1465.3, "duration": 4.05}, {"text": "All right.", "start": 1469.35, "duration": 0.5}, {"text": "Now, the simplest\nthing, of course,", "start": 1469.85, "duration": 2.14}, {"text": "would just be to send\nthe oxaloacetate back out", "start": 1471.99, "duration": 2.48}, {"text": "to the cytosol.", "start": 1474.47, "duration": 2.01}, {"text": "But that's not what happens.", "start": 1476.48, "duration": 1.92}, {"text": "Instead, what happens is\nyou turn that oxaloacetate", "start": 1478.4, "duration": 4.2}, {"text": "into aspartate.", "start": 1482.6, "duration": 2.86}, {"text": "This is an alpha-keto acid.", "start": 1485.46, "duration": 1.62}, {"text": "Turn it into the amino acid.", "start": 1487.08, "duration": 2.28}, {"text": "If you do that, you\nbasically at the same time", "start": 1489.36, "duration": 6.77}, {"text": "turn glutamate into\nalpha-ketoglutarate all right.", "start": 1496.13, "duration": 5.76}, {"text": "Turns out it's that\nalpha-ketoglutarate", "start": 1501.89, "duration": 3.28}, {"text": "that is exchanged when you\nbring malate into the cell.", "start": 1505.17, "duration": 5.72}, {"text": "So malate is exchanged\nfor alpha-ketoglutarate.", "start": 1510.89, "duration": 4.83}, {"text": "And at the same time, you\nexchange the aspartate", "start": 1515.72, "duration": 25.6}, {"text": "for a glutamate.", "start": 1541.32, "duration": 3.24}, {"text": "All right.", "start": 1560.39, "duration": 1.08}, {"text": "So now you can take\nthat aspartame,", "start": 1561.47, "duration": 4.23}, {"text": "turn it back into oxaloacetate.", "start": 1565.7, "duration": 3.66}, {"text": "To do so you need\nto balance this.", "start": 1569.36, "duration": 3.36}, {"text": "So you return your\nalpha-ketoglutarate back", "start": 1572.72, "duration": 6.83}, {"text": "into glutamate.", "start": 1579.55, "duration": 2.07}, {"text": "And effectively, this is the\nmalate aspartate shuttle.", "start": 1581.62, "duration": 11.34}, {"text": "OK.", "start": 1592.96, "duration": 0.57}, {"text": "So electrons from oxaloacetate\nto malate, and then malate back", "start": 1593.53, "duration": 8.06}, {"text": "to oxaloacetate moves\nthe electrons on NADH", "start": 1601.59, "duration": 3.18}, {"text": "from the cytosol into\nthe mitochondria.", "start": 1604.77, "duration": 3.12}, {"text": "To get that malate\nacross the membrane,", "start": 1607.89, "duration": 2.07}, {"text": "you exchange it for\nalpha-ketoglutarate", "start": 1609.96, "duration": 2.43}, {"text": "and to maintain carbon\nbalance across the--", "start": 1612.39, "duration": 3.09}, {"text": "and nitrogen balance--\nacross the whole thing.", "start": 1615.48, "duration": 2.55}, {"text": "At the same time, you\nalso exchange an aspartate", "start": 1618.03, "duration": 3.81}, {"text": "for a glutamate, which allows\nyou to basically interconvert", "start": 1621.84, "duration": 8.33}, {"text": "the oxaloacetate\nand the aspartate", "start": 1630.17, "duration": 3.21}, {"text": "on either side of the\nmembrane via interconverting", "start": 1633.38, "duration": 3.27}, {"text": "glutamate and\nalpha-ketoglutarate.", "start": 1636.65, "duration": 2.79}, {"text": "So somewhat confusing\nsystems, but", "start": 1639.44, "duration": 4.47}, {"text": "recognize that the net\neffect is moving NADH", "start": 1643.91, "duration": 3.93}, {"text": "from one side of the\nmembrane to the other.", "start": 1647.84, "duration": 2.65}, {"text": "And that occurs because you're\ninterconverting to redox pairs", "start": 1650.49, "duration": 4.25}, {"text": "in opposite directions-- in this\ncase oxaloacetate and malate--", "start": 1654.74, "duration": 3.51}, {"text": "on either side of the membrane.", "start": 1658.25, "duration": 2.61}, {"text": "And that's why what\nI alluded to earlier,", "start": 1660.86, "duration": 3.85}, {"text": "you can imagine that\nyou could easily come up", "start": 1664.71, "duration": 3.11}, {"text": "with other shuttle systems\nwhere you have a redox", "start": 1667.82, "duration": 2.61}, {"text": "reaction on one\nside of the membrane", "start": 1670.43, "duration": 1.98}, {"text": "and the reverse of that redox\nreaction on the other side", "start": 1672.41, "duration": 2.4}, {"text": "of the membrane.", "start": 1674.81, "duration": 0.99}, {"text": "And as long as you can\nmaintain carbon balance,", "start": 1675.8, "duration": 2.64}, {"text": "the net effect is moving\nelectrons across the membranes", "start": 1678.44, "duration": 4.14}, {"text": "from one compartment to another.", "start": 1682.58, "duration": 2.34}, {"text": "And that is a way to allow\nyou to generate NADH that's", "start": 1684.92, "duration": 4.89}, {"text": "now in the matrix,\nwhich has access", "start": 1689.81, "duration": 1.95}, {"text": "to complex I of the\nelectron transport chain", "start": 1691.76, "duration": 3.45}, {"text": "as we discussed\nnow several time.", "start": 1695.21, "duration": 5.02}, {"text": "All right.", "start": 1700.23, "duration": 0.9}, {"text": "Now we're ready to go through\nand discuss the accounting", "start": 1701.13, "duration": 5.88}, {"text": "that you see--", "start": 1707.01, "duration": 2.31}, {"text": "the accounting that comes up all\nthe time that is in textbooks", "start": 1713.39, "duration": 4.74}, {"text": "and perhaps you memorized\nfrom previous classes", "start": 1718.13, "duration": 3.03}, {"text": "about how the ATP yield\nworks for different pathways.", "start": 1721.16, "duration": 5.4}, {"text": "So hopefully it's\nclear to you by now", "start": 1726.56, "duration": 1.98}, {"text": "that these numbers that\nyou get are estimates.", "start": 1728.54, "duration": 3.91}, {"text": "And that's because there\nis no direct relationship", "start": 1732.45, "duration": 3.38}, {"text": "between NADH or FADH to NATP.", "start": 1735.83, "duration": 5.05}, {"text": "These interconversions occur\nvia oxidative phosphorylation,", "start": 1740.88, "duration": 3.96}, {"text": "these electron transport\nchains, delta psi/delta pH.", "start": 1744.84, "duration": 3.96}, {"text": "And so all of these\nestimates take", "start": 1748.8, "duration": 2.1}, {"text": "into account various\nassumptions about how efficient", "start": 1750.9, "duration": 4.74}, {"text": "the electron transport chain\nis, oxidative phosphorylation", "start": 1755.64, "duration": 3.18}, {"text": "works, bounded, of\ncourse, by the change", "start": 1758.82, "duration": 4.83}, {"text": "in standard reduction potential,\nwhat's the free energy released", "start": 1763.65, "duration": 3.99}, {"text": "from that?", "start": 1767.64, "duration": 0.87}, {"text": "What's the free energy\nto synthesize ADP to ATP.", "start": 1768.51, "duration": 4.68}, {"text": "Of course, those\nrequire assumptions.", "start": 1773.19, "duration": 2.55}, {"text": "And it's, in the end, why if\nyou read different textbooks", "start": 1775.74, "duration": 4.68}, {"text": "and different sources\nyou will find numbers", "start": 1780.42, "duration": 2.7}, {"text": "that are actually a range.", "start": 1783.12, "duration": 1.69}, {"text": "There is no fixed number\nfor what the equivalent is", "start": 1784.81, "duration": 4.61}, {"text": "of an ATP for an NADH.", "start": 1789.42, "duration": 2.34}, {"text": "And that's because it really\ndepends on several variables.", "start": 1791.76, "duration": 3.19}, {"text": "So let's go through what\nthose variables are,", "start": 1794.95, "duration": 3.56}, {"text": "because if we can\nunderstand that,", "start": 1798.51, "duration": 1.44}, {"text": "you really understand\nhow this system works.", "start": 1799.95, "duration": 3.5}, {"text": "So the first variable--", "start": 1803.45, "duration": 1.97}, {"text": "at least if we're talking\nabout something like glucose,", "start": 1805.42, "duration": 2.79}, {"text": "where we generate\nNADH in the cytosol,", "start": 1808.21, "duration": 3.97}, {"text": "we have to consider\nthe redox shuttles.", "start": 1812.18, "duration": 4.91}, {"text": "And hopefully you appreciate\nnow that you have this need", "start": 1817.09, "duration": 4.02}, {"text": "to regenerate NAD in the cytosol\nto keep glycolysis going.", "start": 1821.11, "duration": 3.45}, {"text": "You got to get those electrons\nsomehow to the electron", "start": 1824.56, "duration": 2.49}, {"text": "transport chain.", "start": 1827.05, "duration": 1.26}, {"text": "And I just described for you two\ndifferent ways you can do that.", "start": 1828.31, "duration": 4.44}, {"text": "Now, if I use the glycerol\nphosphate shuttle,", "start": 1832.75, "duration": 2.22}, {"text": "I'm skipping complex\nI altogether.", "start": 1834.97, "duration": 2.89}, {"text": "And so that's not\npumping any protons.", "start": 1837.86, "duration": 2.18}, {"text": "If I'm using the malate\naspartate shuttle,", "start": 1840.04, "duration": 2.58}, {"text": "well, I have all the energetics\nof doing this gymnastics.", "start": 1842.62, "duration": 3.0}, {"text": "But in the end, now I can use\ncomplex I and pump protons.", "start": 1845.62, "duration": 4.59}, {"text": "And so the yield of ATP,\nif you will-- how many", "start": 1850.21, "duration": 4.5}, {"text": "protons I can pump to generate\ndelta psi/delta pH will", "start": 1854.71, "duration": 4.47}, {"text": "be different if I use\nthe glycerol phosphate", "start": 1859.18, "duration": 2.19}, {"text": "shuttle or a shuttle like\nthe malate aspartate shuttle.", "start": 1861.37, "duration": 5.0}, {"text": "The second variable\nin consideration", "start": 1866.37, "duration": 3.03}, {"text": "is, what is the\nefficiency of proton", "start": 1869.4, "duration": 6.15}, {"text": "pumping by the various electron\ntransport chain ETC complexes?", "start": 1875.55, "duration": 9.12}, {"text": "That's not so straightforward\nand, of course,", "start": 1889.31, "duration": 3.73}, {"text": "is going to depend on\na couple of things.", "start": 1893.04, "duration": 2.81}, {"text": "Remember, we spent a long\ntime talking about ATP/ADP,", "start": 1895.85, "duration": 3.81}, {"text": "and how it's the ratio of\nATP/ADP that was really", "start": 1899.66, "duration": 3.6}, {"text": "the energy there,\nbecause, remember,", "start": 1903.26, "duration": 1.92}, {"text": "thermodynamics is\ndependent on that log", "start": 1905.18, "duration": 3.93}, {"text": "of the reactants over the\nproduct's term in the delta G", "start": 1909.11, "duration": 3.69}, {"text": "equation.", "start": 1912.8, "duration": 1.42}, {"text": "Well, that's true also\nfor the NAD/NADH ratio.", "start": 1914.22, "duration": 4.28}, {"text": "And it's also true for how\nhigh the membrane potential is.", "start": 1918.5, "duration": 3.15}, {"text": "And so how efficient\nthis pumping", "start": 1921.65, "duration": 2.55}, {"text": "is going to be is going\nto be depending on what", "start": 1924.2, "duration": 2.73}, {"text": "is the delta psi to begin with,\nand what is the NAD/NADH ratio", "start": 1926.93, "duration": 3.87}, {"text": "or the FAD/FADH2 ratio,\nbecause all of those things", "start": 1930.8, "duration": 4.89}, {"text": "will affect how much\nfree energy there", "start": 1935.69, "duration": 2.46}, {"text": "is to be able to move protons\nfrom one side of the membrane", "start": 1938.15, "duration": 3.78}, {"text": "to the other.", "start": 1941.93, "duration": 2.61}, {"text": "Once I get those protons\nacross the membrane,", "start": 1944.54, "duration": 2.64}, {"text": "then there's the\nquestion of how--", "start": 1947.18, "duration": 3.3}, {"text": "and for lack of a\nbetter word, I'm", "start": 1950.48, "duration": 1.53}, {"text": "going to say tight the\nmembrane is to proton leak.", "start": 1952.01, "duration": 9.71}, {"text": "That is, you can imagine\nthat to make ATP,", "start": 1961.72, "duration": 3.48}, {"text": "I have to send\nthose protons back", "start": 1965.2, "duration": 2.22}, {"text": "through the ATP synthase,\ncomplex V, F1F0-ATPase,", "start": 1967.42, "duration": 3.51}, {"text": "whatever you want to call it.", "start": 1970.93, "duration": 2.08}, {"text": "And if some of\nthose protons just", "start": 1973.01, "duration": 2.18}, {"text": "leak back across the\nmembrane, well, that's", "start": 1975.19, "duration": 2.97}, {"text": "how we generate heat.", "start": 1978.16, "duration": 1.56}, {"text": "And so how tight\nthat membrane is,", "start": 1979.72, "duration": 2.76}, {"text": "that is how coupled\ndelta psi is,", "start": 1982.48, "duration": 6.9}, {"text": "delta pH is to ATP synthesis\nis another variable.", "start": 1989.38, "duration": 5.95}, {"text": "And of course, the last one is,\nis the efficiency of H+ turning", "start": 1995.33, "duration": 12.85}, {"text": "the F0F1-ATPase, which is the\nsame considerations that we", "start": 2008.18, "duration": 5.55}, {"text": "already talked about\nfor number two.", "start": 2013.73, "duration": 1.5}, {"text": "That is, the higher delta\npsi/delta pH, the more free", "start": 2015.23, "duration": 3.93}, {"text": "energy that's stored there\nand the higher or lower", "start": 2019.16, "duration": 3.69}, {"text": "the ATP/ADP ratio is, the easier\nor harder it is to synthesize", "start": 2022.85, "duration": 6.18}, {"text": "ADP.", "start": 2029.03, "duration": 1.5}, {"text": "And so basically,\nthese different things,", "start": 2030.53, "duration": 4.26}, {"text": "two through four, in\ngeneral takes into account", "start": 2034.79, "duration": 5.25}, {"text": "a term called\ncoupled respiration.", "start": 2040.04, "duration": 5.25}, {"text": "By coupled\nrespiration is really,", "start": 2045.29, "duration": 2.43}, {"text": "how tightly is oxidation--", "start": 2047.72, "duration": 3.15}, {"text": "moving electrons on the electron\ntransport chain to oxygen--", "start": 2050.87, "duration": 3.36}, {"text": "to phosphorylation--\nsynthesizing ATP from ADP?", "start": 2054.23, "duration": 5.46}, {"text": "And so, how tight\nor how well-coupled", "start": 2059.69, "duration": 3.6}, {"text": "is respiration to\nphosphorylation really", "start": 2063.29, "duration": 5.429}, {"text": "is a variable that is going to\nvery much depend on conditions.", "start": 2068.719, "duration": 5.641}, {"text": "And so ultimately,\nto give numbers", "start": 2074.36, "duration": 3.48}, {"text": "for what is the ATP produced\nfrom various oxidation", "start": 2077.84, "duration": 4.29}, {"text": "processes, one has\nto make assumptions", "start": 2082.13, "duration": 2.58}, {"text": "about all of these things,\nhow coupled respiration is", "start": 2084.71, "duration": 2.85}, {"text": "and which redox\nshuttles are used?", "start": 2087.56, "duration": 1.619}, {"text": "If it's something\nlike glycolysis,", "start": 2089.179, "duration": 2.04}, {"text": "it involves the cytosol.", "start": 2091.219, "duration": 2.821}, {"text": "And this is why these\nnumbers are made up.", "start": 2094.04, "duration": 2.13}, {"text": "And it makes no sense in my\nview to memorize these numbers.", "start": 2096.17, "duration": 4.32}, {"text": "But I think it is\nimportant to understand", "start": 2100.49, "duration": 3.54}, {"text": "where those numbers come from.", "start": 2104.03, "duration": 2.14}, {"text": "Because if you understand\nthat, that means you understand", "start": 2106.17, "duration": 2.99}, {"text": "all the assumptions and why\nthe numbers are variable,", "start": 2109.16, "duration": 3.54}, {"text": "you really understand\nthe bioenergetics", "start": 2112.7, "duration": 2.55}, {"text": "of what's going\non in metabolism.", "start": 2115.25, "duration": 2.62}, {"text": "All right.", "start": 2117.87, "duration": 0.5}, {"text": "So now let's go through\none of these calculations", "start": 2118.37, "duration": 3.39}, {"text": "just to fully illustrate\nwhat I'm talking about.", "start": 2121.76, "duration": 3.58}, {"text": "So let's go through the\ncalculation for glycolysis.", "start": 2125.34, "duration": 2.59}, {"text": "So if I run glycolysis and\nturn glucose into two pyruvate.", "start": 2127.93, "duration": 6.97}, {"text": "So what do we get from that?", "start": 2134.9, "duration": 3.2}, {"text": "Of course, we get\n2 ATPs produced", "start": 2138.1, "duration": 4.06}, {"text": "and we get two NADHs\nproduced in the cytosol.", "start": 2142.16, "duration": 6.41}, {"text": "OK.", "start": 2148.57, "duration": 2.37}, {"text": "So this is the cytosol.", "start": 2150.94, "duration": 3.35}, {"text": "This is the mitochondria.", "start": 2154.29, "duration": 1.56}, {"text": "All right?", "start": 2155.85, "duration": 1.45}, {"text": "We're going to completely\noxidize that pyruvate.", "start": 2157.3, "duration": 2.24}, {"text": "We send that pyruvate\ninto the mitochondria.", "start": 2159.54, "duration": 3.6}, {"text": "We run the PDH reaction.", "start": 2167.89, "duration": 2.92}, {"text": "That gives us two\nacetyl-CoA, which", "start": 2170.81, "duration": 3.66}, {"text": "is a yield of two more NADHs.", "start": 2174.47, "duration": 6.49}, {"text": "All right?", "start": 2180.96, "duration": 1.05}, {"text": "If we now take those acetyl-CoAs\nand we burn them completely,", "start": 2182.01, "duration": 5.64}, {"text": "two cycles around the TCA cycle.", "start": 2187.65, "duration": 3.6}, {"text": "OK, now we get two more\nFADH2s and six NADHs--", "start": 2191.25, "duration": 11.93}, {"text": "one FADH2, three NADHs from\neach turn, as well as a GDP.", "start": 2203.18, "duration": 4.53}, {"text": "And so that's a total of two\nFADH2, six NADHs, and two GTPs.", "start": 2207.71, "duration": 6.54}, {"text": "And so now if I come\ntogether, what is our yield?", "start": 2214.25, "duration": 5.19}, {"text": "Well, from the\nmitochondria I've generated", "start": 2219.44, "duration": 3.81}, {"text": "a total of two FADH2s and\nsix, seven, eight NADHs.", "start": 2223.25, "duration": 7.004}, {"text": "And then up here, there's\nan additional two NADHs", "start": 2233.0, "duration": 5.28}, {"text": "that are made in\nthe cytosol, and so", "start": 2238.28, "duration": 2.4}, {"text": "have to access the electron\ntransport chain via a shuttle.", "start": 2240.68, "duration": 5.63}, {"text": "A typical number that's\ngiven is you get 1.58 ATP", "start": 2246.31, "duration": 5.58}, {"text": "for something that has\nto access via shuttle,", "start": 2251.89, "duration": 3.36}, {"text": "or on FADH2, that\nwould make sense,", "start": 2255.25, "duration": 5.52}, {"text": "because FADH2 is really the\nsame as a glycerol phosphate", "start": 2260.77, "duration": 3.6}, {"text": "shuttle.", "start": 2264.37, "duration": 0.87}, {"text": "And so if I do that, that\nwould be three ATP from the two", "start": 2265.24, "duration": 5.34}, {"text": "glycolysis NADHs and three ATP\nfrom the two TCA cycle FADH2s,", "start": 2270.58, "duration": 10.14}, {"text": "because the NADHs produced\nin the matrix can generate", "start": 2280.72, "duration": 5.22}, {"text": "POM protons via complex I.\nOftentimes, that's said to be,", "start": 2285.94, "duration": 3.99}, {"text": "oh, that's about 2 and 1/2 ATP.", "start": 2289.93, "duration": 2.22}, {"text": "So 8 times 2.5 is 20 ATP.", "start": 2292.15, "duration": 3.91}, {"text": "And if we had all\nthese numbers together,", "start": 2296.06, "duration": 1.73}, {"text": "20 plus 3 plus 3 plus 2 plus\n2, that is a total of 30", "start": 2297.79, "duration": 9.42}, {"text": "ATP per glucose that's\ncompletely oxidized to CO2.", "start": 2307.21, "duration": 7.83}, {"text": "OK?", "start": 2315.04, "duration": 1.14}, {"text": "So 26 ATP over here plus another\n2 from GTP plus another 2", "start": 2316.18, "duration": 9.83}, {"text": "from glycolysis is a total\nof 20 ATP per glucose.", "start": 2326.01, "duration": 4.56}, {"text": "That is a number.", "start": 2330.57, "duration": 0.9}, {"text": "It made certain assumptions.", "start": 2331.47, "duration": 1.53}, {"text": "Obviously, if I assume that this\nis not the glycerol phosphate", "start": 2333.0, "duration": 5.4}, {"text": "shuttle but instead the\nmalate aspartate shuttle,", "start": 2338.4, "duration": 2.4}, {"text": "maybe I bump this number up\nby multiplying that by 2.5.", "start": 2340.8, "duration": 4.35}, {"text": "Maybe I use different\nconversion factors.", "start": 2345.15, "duration": 3.09}, {"text": "And if you read\nin textbooks, you", "start": 2348.24, "duration": 2.37}, {"text": "get numbers that\nrange from 30 to 36.", "start": 2350.61, "duration": 3.48}, {"text": "I think the highest I've ever\nseen is 38 ATP per glucose.", "start": 2354.09, "duration": 5.4}, {"text": "And the fact that you\nactually see this range really", "start": 2359.49, "duration": 2.88}, {"text": "reflects the different\nauthors of textbooks,", "start": 2362.37, "duration": 3.66}, {"text": "or whoever writes these things,\nmakes different assumptions", "start": 2366.03, "duration": 3.09}, {"text": "about all of these\nthings over here", "start": 2369.12, "duration": 3.51}, {"text": "to understand how to\nmake these conversions.", "start": 2372.63, "duration": 2.55}, {"text": "But the important thing is\nrealizing that these are not", "start": 2375.18, "duration": 2.4}, {"text": "real numbers.", "start": 2377.58, "duration": 1.64}, {"text": "All right.", "start": 2379.22, "duration": 0.5}, {"text": "Let's quickly go\nthrough and just do", "start": 2379.72, "duration": 2.43}, {"text": "the similar exercise one last\ntime just to come back to.", "start": 2382.15, "duration": 2.94}, {"text": "I'm not going to go\nthrough as much detail.", "start": 2385.09, "duration": 2.52}, {"text": "But we talked about\nthat 6:0 fatty acid", "start": 2387.61, "duration": 3.03}, {"text": "that we did accounting\nfor earlier.", "start": 2390.64, "duration": 2.01}, {"text": "If you look back in your\nnotes, what we wrote down", "start": 2392.65, "duration": 2.79}, {"text": "is that from completely\noxidizing that fully saturated", "start": 2395.44, "duration": 4.77}, {"text": "six carbon fatty acid, we got\none ATP, 11 and ADHDs, and five", "start": 2400.21, "duration": 9.76}, {"text": "FADH2s.", "start": 2409.97, "duration": 0.5}, {"text": "Remember, all these\nare being generated", "start": 2413.96, "duration": 2.3}, {"text": "in the-- all these NADHs\nand FADH2s are already", "start": 2416.26, "duration": 4.59}, {"text": "in the mitochondria.", "start": 2420.85, "duration": 1.47}, {"text": "And so if we just use the\nsame conversion factors", "start": 2422.32, "duration": 3.75}, {"text": "that we used for over there in\nour calculation for glycolysis,", "start": 2426.07, "duration": 5.1}, {"text": "what we get is 27.5 ATP\nfor the NADHs and 7.5 ATP", "start": 2431.17, "duration": 13.11}, {"text": "for the FADH2s, which is\na total of 35 ATP for--", "start": 2444.28, "duration": 10.36}, {"text": "35 plus the one,\nso a total of 36", "start": 2458.13, "duration": 7.19}, {"text": "ATP from complete oxidation\nof our six carbon fatty acid,", "start": 2465.32, "duration": 6.007}, {"text": "which is certainly\ngreater than the 30", "start": 2471.327, "duration": 1.583}, {"text": "ATP we got from complete\noxidation of glucose.", "start": 2472.91, "duration": 4.29}, {"text": "That makes sense.", "start": 2477.2, "duration": 1.53}, {"text": "Fatty acids are more\nreduced than glucose--", "start": 2478.73, "duration": 2.73}, {"text": "more calories, should be\nable to get more from it.", "start": 2481.46, "duration": 3.18}, {"text": "And this calculation\nillustrates that we get that.", "start": 2484.64, "duration": 3.83}, {"text": "The typical\ncalculation in textbook", "start": 2488.47, "duration": 2.64}, {"text": "usually describes complete\noxidation of a 16:0--", "start": 2491.11, "duration": 4.62}, {"text": "a fully saturated 16\ncarbon fatty acid.", "start": 2495.73, "duration": 3.87}, {"text": "That's palmitate.", "start": 2499.6, "duration": 0.93}, {"text": "That's one of the most abundant\nfatty acids in the cell.", "start": 2500.53, "duration": 3.3}, {"text": "This, if you\ncompletely oxidize it,", "start": 2503.83, "duration": 2.52}, {"text": "the number and a\nlot of textbooks", "start": 2506.35, "duration": 2.07}, {"text": "is 106 ATP per palmitate\ncompletely oxidized to CO2.", "start": 2508.42, "duration": 9.12}, {"text": "If you're so inclined,\nyou can go through", "start": 2517.54, "duration": 2.25}, {"text": "and do the calculations yourself\nand see if you agree with that.", "start": 2519.79, "duration": 4.36}, {"text": "But the key point of all of this\naccounting is that none of this", "start": 2524.15, "duration": 3.2}, {"text": "are real numbers.", "start": 2527.35, "duration": 1.63}, {"text": "And I hope you now\nbetter appreciate", "start": 2528.98, "duration": 2.87}, {"text": "what energy really means--", "start": 2531.85, "duration": 2.88}, {"text": "that is, how oxidation of\ncarbon by being favorable", "start": 2534.73, "duration": 4.71}, {"text": "can be coupled either to direct\ncharging of an ATP/ADT ratio", "start": 2539.44, "duration": 6.78}, {"text": "as occurs in the GAPDH\nstep of glycolysis,", "start": 2546.22, "duration": 5.22}, {"text": "as well as the\nsuccinic thiokinase", "start": 2551.44, "duration": 2.94}, {"text": "step of the TCA cycle.", "start": 2554.38, "duration": 1.95}, {"text": "But most energy\ntransduction involves", "start": 2556.33, "duration": 3.18}, {"text": "this charging up\nNAD/NADH ratios,", "start": 2559.51, "duration": 4.29}, {"text": "or reactions that are\ncoupled to FAD/FADH2", "start": 2563.8, "duration": 3.87}, {"text": "via these membrane complexes\nthat ultimately lead", "start": 2567.67, "duration": 4.38}, {"text": "to this favorable\nelectron transport", "start": 2572.05, "duration": 2.88}, {"text": "from lower to higher standard\nreduction potentials.", "start": 2574.93, "duration": 4.77}, {"text": "That favorable\nelectron transport", "start": 2579.7, "duration": 2.46}, {"text": "can be used to create a battery,\na delta psi/delta pH, which", "start": 2582.16, "duration": 3.87}, {"text": "can then be coupled\nto do other work,", "start": 2586.03, "duration": 2.44}, {"text": "including synthesizing ATP at\nthe high ATP/ADP ratio that", "start": 2588.47, "duration": 4.7}, {"text": "can then be used\nby other reactions", "start": 2593.17, "duration": 2.46}, {"text": "in the cell that would otherwise\nbe unfavorable and allow cells", "start": 2595.63, "duration": 4.47}, {"text": "to basically extract\nenergy from its environment", "start": 2600.1, "duration": 3.69}, {"text": "in order to fuel the processes\nthat are unfavorable and are", "start": 2603.79, "duration": 4.74}, {"text": "necessary to sustain life.", "start": 2608.53, "duration": 3.33}, {"text": "All right.", "start": 2611.86, "duration": 1.925}, {"text": "Great.", "start": 2613.785, "duration": 0.5}, {"text": "So thus far, we have\nfocused almost entirely", "start": 2620.51, "duration": 6.76}, {"text": "on how you oxidized carbon\nas a way to release energy.", "start": 2627.27, "duration": 6.89}, {"text": "And that's great.", "start": 2634.16, "duration": 1.43}, {"text": "But of course,\nthat reduced carbon", "start": 2635.59, "duration": 2.29}, {"text": "has to come from\nsomewhere to begin with.", "start": 2637.88, "duration": 3.42}, {"text": "And every one of us\nlearned in grade school", "start": 2641.3, "duration": 3.57}, {"text": "that the energy for all life\nultimately comes from the sun.", "start": 2644.87, "duration": 4.35}, {"text": "And that's, of course,\nphotosynthesis.", "start": 2649.22, "duration": 1.86}, {"text": "And now I want to\nturn to beginning", "start": 2651.08, "duration": 2.52}, {"text": "to discuss photosynthesis\nand how it works.", "start": 2653.6, "duration": 4.51}, {"text": "In other words, how does\nlife harvest solar energy", "start": 2658.11, "duration": 3.77}, {"text": "in a usable form that ultimately\ninvolves using atmospheric CO2,", "start": 2661.88, "duration": 9.67}, {"text": "which gets reduced\nto generate reduced", "start": 2671.55, "duration": 3.99}, {"text": "carbon that, of\ncourse, originally", "start": 2675.54, "duration": 2.52}, {"text": "occurred because plants--", "start": 2678.06, "duration": 2.73}, {"text": "or, any photosynthetic organism\nhas the same issues as us.", "start": 2680.79, "duration": 4.2}, {"text": "That is, to fight\nthermodynamics, maintain,", "start": 2684.99, "duration": 3.66}, {"text": "and survive.", "start": 2688.65, "duration": 1.08}, {"text": "It constantly has to be charging\nan ATP/ADP ratio in order", "start": 2689.73, "duration": 4.68}, {"text": "to fuel the otherwise\nunfavorable processes that", "start": 2694.41, "duration": 3.66}, {"text": "are required to maintain\norder in the cell.", "start": 2698.07, "duration": 4.53}, {"text": "This has to occur during\nthe day when the sun is out", "start": 2702.6, "duration": 2.85}, {"text": "and there's light\nenergy photosynthesis.", "start": 2705.45, "duration": 2.7}, {"text": "But also has to occur\nat night, or at times", "start": 2708.15, "duration": 2.67}, {"text": "when there is no sun.", "start": 2710.82, "duration": 1.5}, {"text": "And so thus, plants basically\nstored energy as reduced carbon", "start": 2712.32, "duration": 6.75}, {"text": "so that they had something\nto eat at night-- that is,", "start": 2719.07, "duration": 2.7}, {"text": "to keep their\nATP/ADP ratios high--", "start": 2721.77, "duration": 2.85}, {"text": "at night so they can do all\nthese catabolic processes", "start": 2724.62, "duration": 3.21}, {"text": "at night.", "start": 2727.83, "duration": 1.38}, {"text": "Now, fortunately\nfor us, the fact", "start": 2729.21, "duration": 3.33}, {"text": "that photosynthetic organisms\nstored all this reduced carbon", "start": 2732.54, "duration": 4.05}, {"text": "allowed other life,\nlike us, to evolve", "start": 2736.59, "duration": 3.36}, {"text": "that is entirely dependent\non photosynthetic organisms", "start": 2739.95, "duration": 5.25}, {"text": "either directly or\nindirectly for food.", "start": 2745.2, "duration": 4.18}, {"text": "And so photosynthesis also is\nthe process that ultimately", "start": 2749.38, "duration": 5.78}, {"text": "oxygenated our atmosphere.", "start": 2755.16, "duration": 4.51}, {"text": "Aerobic life, also something\nthat was necessary for us", "start": 2759.67, "duration": 3.45}, {"text": "to survive because oxygen is\nsuch a key electron acceptor,", "start": 2763.12, "duration": 4.65}, {"text": "really key to our energetics--", "start": 2767.77, "duration": 2.98}, {"text": "well, the fact that\nphotosynthetic organisms", "start": 2770.75, "duration": 2.39}, {"text": "put oxygen in our\natmosphere also", "start": 2773.14, "duration": 3.06}, {"text": "was really essential for aerobic\nlife, us, to ultimately evolve.", "start": 2776.2, "duration": 7.17}, {"text": "And so photosynthesis is often,\nin biochemistry courses, almost", "start": 2783.37, "duration": 5.16}, {"text": "a sidelight and\nforgotten process.", "start": 2788.53, "duration": 3.13}, {"text": "But of course, it is\nreally, really central", "start": 2791.66, "duration": 2.75}, {"text": "to how life works,\nbecause no life", "start": 2794.41, "duration": 2.43}, {"text": "could exist without\nphotosynthesis", "start": 2796.84, "duration": 2.1}, {"text": "and the conditions\nthat allowed aerobic--", "start": 2798.94, "duration": 2.76}, {"text": "most multicellular\nlife that we know", "start": 2801.7, "duration": 2.01}, {"text": "of that's not photosynthetic,\nincluding ourselves,", "start": 2803.71, "duration": 3.18}, {"text": "could not have evolved\nwithout photosynthesis", "start": 2806.89, "duration": 3.24}, {"text": "oxygenating the\natmosphere and generating", "start": 2810.13, "duration": 2.64}, {"text": "all this reduced carbon.", "start": 2812.77, "duration": 1.62}, {"text": "That, really, is where we\nget our energy from as food.", "start": 2814.39, "duration": 4.98}, {"text": "Now, you also learned\nin grade school,", "start": 2819.37, "duration": 3.39}, {"text": "when you learned that life\ndepends on energy of the sun,", "start": 2822.76, "duration": 3.57}, {"text": "that the process\nthat life uses is", "start": 2826.33, "duration": 3.06}, {"text": "this mysterious photosynthesis.", "start": 2829.39, "duration": 3.69}, {"text": "Well, as we go through\nthis over the rest of today", "start": 2833.08, "duration": 2.28}, {"text": "and in the next lecture,\nI want you to appreciate", "start": 2835.36, "duration": 2.43}, {"text": "what photosynthesis is.", "start": 2837.79, "duration": 2.43}, {"text": "And that is how life\nreally takes solar energy", "start": 2840.22, "duration": 5.91}, {"text": "and harvests that energy in\na biologically useful form,", "start": 2846.13, "duration": 4.86}, {"text": "bearing in mind all of the\nconcepts that we've already", "start": 2850.99, "duration": 4.32}, {"text": "talked about, because that will\nultimately help you understand", "start": 2855.31, "duration": 5.8}, {"text": "how that energy from the\nsun is used to make all", "start": 2861.11, "duration": 4.62}, {"text": "this reduced carbon,\nthis carbohydrate and fat", "start": 2865.73, "duration": 3.45}, {"text": "that is energy that we can use\nfor later, and also, of course,", "start": 2869.18, "duration": 4.24}, {"text": "allows how photosynthetic\norganisms can use light", "start": 2873.42, "duration": 3.8}, {"text": "from the sun to just\npower things directly", "start": 2877.22, "duration": 2.46}, {"text": "from that solar battery,\nand ultimately, of course,", "start": 2879.68, "duration": 4.41}, {"text": "you should appreciate that\nthese things all came first.", "start": 2884.09, "duration": 4.94}, {"text": "Photosynthesis\nobviously existed first.", "start": 2889.03, "duration": 2.7}, {"text": "And so most of what we\nalready talked about--", "start": 2891.73, "duration": 2.79}, {"text": "well, we'll draw parallels when\nwe talk about photosynthesis", "start": 2894.52, "duration": 3.18}, {"text": "to the stuff we already know.", "start": 2897.7, "duration": 1.62}, {"text": "Of course, photosynthesis\ncame first.", "start": 2899.32, "duration": 1.97}, {"text": "And the stuff you've\nalready learned about", "start": 2901.29, "duration": 1.75}, {"text": "evolved from photosynthesis.", "start": 2903.04, "duration": 3.45}, {"text": "All right.", "start": 2906.49, "duration": 1.11}, {"text": "Now, like all pathways,\nphotosynthesis also", "start": 2907.6, "duration": 4.17}, {"text": "has to follow the same rules\nand laws of thermodynamics that", "start": 2911.77, "duration": 3.9}, {"text": "were true for all pathways.", "start": 2915.67, "duration": 1.86}, {"text": "So plants and animals have\nto follow the same rules.", "start": 2917.53, "duration": 4.36}, {"text": "And so what is photosynthesis?", "start": 2921.89, "duration": 2.33}, {"text": "Well, it's ultimately CO2\nin the atmosphere that", "start": 2924.22, "duration": 4.62}, {"text": "gets reduced to carbohydrate.", "start": 2928.84, "duration": 4.26}, {"text": "That's classically\nphotosynthesis.", "start": 2936.5, "duration": 1.74}, {"text": "But, of course, plants\nalso make fatty acids.", "start": 2938.24, "duration": 4.83}, {"text": "OK?", "start": 2943.07, "duration": 1.38}, {"text": "This is carbon reduction.", "start": 2944.45, "duration": 4.38}, {"text": "Remember, carbon oxidation\ngenerally is favorable.", "start": 2948.83, "duration": 4.26}, {"text": "Carbon reduction is not.", "start": 2953.09, "duration": 2.25}, {"text": "Delta G naught prime for\nthis is greater than 0.", "start": 2955.34, "duration": 5.49}, {"text": "This direction is favored.", "start": 2960.83, "duration": 1.68}, {"text": "That direction is\nnot, which means", "start": 2962.51, "duration": 2.25}, {"text": "you need energy input\nto reduce that CO2", "start": 2964.76, "duration": 3.99}, {"text": "to carbohydrate or fatty acid.", "start": 2968.75, "duration": 2.19}, {"text": "And of course, it's the sun's\nenergy, the solar energy,", "start": 2970.94, "duration": 4.35}, {"text": "that ultimately must be\ndone to make this favorable.", "start": 2975.29, "duration": 5.24}, {"text": "Now we're reducing carbon.", "start": 2980.53, "duration": 2.43}, {"text": "That means we need\nto add electrons.", "start": 2982.96, "duration": 2.79}, {"text": "Those electrons have\nto come from somewhere.", "start": 2985.75, "duration": 2.68}, {"text": "And so we're\nreducing the carbon.", "start": 2988.43, "duration": 3.32}, {"text": "That means something\nelse has to be oxidized.", "start": 2991.75, "duration": 2.46}, {"text": "Just like when we\noxidized carbon,", "start": 2994.21, "duration": 2.34}, {"text": "those electrons had\nto go somewhere,", "start": 2996.55, "duration": 1.62}, {"text": "something else\nhad to be reduced.", "start": 2998.17, "duration": 2.13}, {"text": "That was pyruvate to\nlactate and fermentation,", "start": 3000.3, "duration": 2.61}, {"text": "or oxygen to water via all of\nthe oxidative phosphorylation", "start": 3002.91, "duration": 5.16}, {"text": "things we just talked about.", "start": 3008.07, "duration": 1.62}, {"text": "And so in this case,\nthose electrons", "start": 3009.69, "duration": 1.5}, {"text": "have to come from somewhere.", "start": 3011.19, "duration": 1.51}, {"text": "And those electrons ultimately,\nfor photosynthesis--", "start": 3012.7, "duration": 4.64}, {"text": "this reduction,\nthe electrons come", "start": 3017.34, "duration": 2.31}, {"text": "from oxidation,\nultimately, of water,", "start": 3019.65, "duration": 6.77}, {"text": "which will generate oxygen.\nAnd this is effectively then", "start": 3026.42, "duration": 7.6}, {"text": "the reverse of what\nyou learned about", "start": 3034.02, "duration": 2.37}, {"text": "for the mitochondrial\nelectron transport.", "start": 3036.39, "duration": 3.45}, {"text": "Why this?", "start": 3039.84, "duration": 1.05}, {"text": "Well, water is very abundant,\nhas been for all of life", "start": 3040.89, "duration": 9.09}, {"text": "on Earth.", "start": 3049.98, "duration": 0.72}, {"text": "Water is-- obviously,\nlife depends on water.", "start": 3050.7, "duration": 4.78}, {"text": "And so you can oxidize\nthe water to generate", "start": 3055.48, "duration": 7.34}, {"text": "oxygen. This will obviously\ngenerate electrons that", "start": 3062.82, "duration": 3.21}, {"text": "can be used to reduce carbon.", "start": 3066.03, "duration": 3.36}, {"text": "And it's effectively the\nphotosynthetic oxidation", "start": 3069.39, "duration": 3.75}, {"text": "of water to make oxygen that\nwas the source of oxygen", "start": 3073.14, "duration": 4.83}, {"text": "in the atmosphere\nthat, really, today", "start": 3077.97, "duration": 3.06}, {"text": "makes aerobic life possible.", "start": 3081.03, "duration": 3.01}, {"text": "Now, of course, the fact that\noxygen is a good electron", "start": 3084.04, "duration": 3.318}, {"text": "acceptor-- we've been\ntalking about this forever.", "start": 3087.358, "duration": 2.042}, {"text": "This means that, of\ncourse, you might", "start": 3089.4, "duration": 2.31}, {"text": "guess that delta G naught\nprime for this process", "start": 3091.71, "duration": 4.47}, {"text": "is not going to be favorable.", "start": 3096.18, "duration": 3.48}, {"text": "To put it another way,\noxygen is a great electron", "start": 3099.66, "duration": 3.03}, {"text": "acceptor and water is\na poor electron donor.", "start": 3102.69, "duration": 3.67}, {"text": "And so, really, the\nway photosynthesis--", "start": 3106.36, "duration": 2.99}, {"text": "the magic of\nphotosynthesis, if you will,", "start": 3109.35, "duration": 2.43}, {"text": "is making water a good electron\ndonor, because, ultimately,", "start": 3111.78, "duration": 8.52}, {"text": "that is what is going\nto make this whole thing", "start": 3120.3, "duration": 3.54}, {"text": "work energetically.", "start": 3123.84, "duration": 2.49}, {"text": "And so you probably could guess\nthat if these processes are", "start": 3126.33, "duration": 7.29}, {"text": "really about these\nelectron transfers,", "start": 3133.62, "duration": 2.37}, {"text": "we need electron carriers.", "start": 3135.99, "duration": 1.77}, {"text": "This is true for\nphotosynthesis, just", "start": 3137.76, "duration": 2.7}, {"text": "as it was true for\noxidative phosphorylation.", "start": 3140.46, "duration": 4.62}, {"text": "But remember, we'll describe\na lot of the same electron", "start": 3145.08, "duration": 2.58}, {"text": "carriers that are used.", "start": 3147.66, "duration": 1.17}, {"text": "But as we described\nthem, remember", "start": 3148.83, "duration": 1.68}, {"text": "that the photosynthesis\ncame first.", "start": 3150.51, "duration": 1.9}, {"text": "And so the other processes, like\nOXPHOS, that use these electron", "start": 3152.41, "duration": 4.13}, {"text": "carriers, use them\nbecause they were first", "start": 3156.54, "duration": 1.95}, {"text": "used in photosynthesis.", "start": 3158.49, "duration": 1.5}, {"text": "And then they were repurposed\nfor oxidative phosphorylation.", "start": 3159.99, "duration": 5.62}, {"text": "Now, to discuss this,\nI want to first start", "start": 3165.61, "duration": 2.76}, {"text": "by introducing an\nelectron carrier that's", "start": 3168.37, "duration": 4.17}, {"text": "important for this that's\nreally a variation on NADH.", "start": 3172.54, "duration": 4.83}, {"text": "And it's an electron\ncarrier that's found in--", "start": 3177.37, "duration": 3.15}, {"text": "excuse me-- all plants,\nall animals, all life,", "start": 3180.52, "duration": 4.53}, {"text": "and is very important\nin anabolic pathways", "start": 3185.05, "duration": 3.39}, {"text": "like photosynthesis.", "start": 3188.44, "duration": 2.52}, {"text": "Remember that anabolism,\nbuilding stuff,", "start": 3190.96, "duration": 2.88}, {"text": "has to be distinct from\ncatabolism, breaking stuff", "start": 3193.84, "duration": 3.18}, {"text": "down, for a number of reasons.", "start": 3197.02, "duration": 1.8}, {"text": "We saw this in glycolysis\nand gluconeogenesis, glycogen", "start": 3198.82, "duration": 3.09}, {"text": "synthesis, glycogen breakdown.", "start": 3201.91, "duration": 2.52}, {"text": "Remember, delta G naught prime\ncan only favor one direction.", "start": 3204.43, "duration": 3.73}, {"text": "And so in the direction\nthat's favorable, it works.", "start": 3208.16, "duration": 2.957}, {"text": "In the other direction to\nactually make it happen,", "start": 3211.117, "duration": 2.083}, {"text": "we have to make delta\nG less than zero.", "start": 3213.2, "duration": 2.57}, {"text": "That has to happen\nby energy addition.", "start": 3215.77, "duration": 1.89}, {"text": "And so now we had to have\nthese separate pathways.", "start": 3217.66, "duration": 3.24}, {"text": "You also need separate\npathways because that", "start": 3220.9, "duration": 1.92}, {"text": "allows separate regulation,\navoids futile cycle,", "start": 3222.82, "duration": 3.45}, {"text": "and enables cells to match\nneeds with processes.", "start": 3226.27, "duration": 3.57}, {"text": "And as we already\ndiscussed, one way", "start": 3229.84, "duration": 2.61}, {"text": "to keep these anabolic and\ncatabolic processes distinct", "start": 3232.45, "duration": 3.21}, {"text": "is by building separate\ncompartments, right?", "start": 3235.66, "duration": 2.07}, {"text": "It's useful to have\nseparate compartments,", "start": 3237.73, "duration": 2.133}, {"text": "different conditions in\ndifferent compartments", "start": 3239.863, "duration": 1.917}, {"text": "that can favor different\nthings happening.", "start": 3241.78, "duration": 3.04}, {"text": "However, not all cells\nhave separate compartments.", "start": 3244.82, "duration": 2.81}, {"text": "Prokaryotes don't.", "start": 3247.63, "duration": 1.5}, {"text": "And you might\nthink of situations", "start": 3249.13, "duration": 2.7}, {"text": "where you clearly\nwant to have two", "start": 3251.83, "duration": 2.61}, {"text": "different types of\nreactions happening", "start": 3254.44, "duration": 1.83}, {"text": "in the same compartment.", "start": 3256.27, "duration": 1.41}, {"text": "And so what if you want to\nboth do oxidation and reduction", "start": 3257.68, "duration": 4.44}, {"text": "in different reactions\nin the same compartment?", "start": 3262.12, "duration": 3.11}, {"text": "Well, clearly you\nneed some way that", "start": 3265.23, "duration": 3.4}, {"text": "will favor some\nreactions being oxidation", "start": 3268.63, "duration": 3.15}, {"text": "and other reactions\nbeing reductions.", "start": 3271.78, "duration": 2.82}, {"text": "And if you simply rely on\nNADH/NAD+ as your oxidant", "start": 3274.6, "duration": 8.34}, {"text": "or your reductant, this\nnow becomes a problem.", "start": 3282.94, "duration": 4.55}, {"text": "All right?", "start": 3287.49, "duration": 1.45}, {"text": "So a solution is, well, let's\nmake a distinct electron", "start": 3288.94, "duration": 4.65}, {"text": "carrier for the oxidation\nreactions in the cells.", "start": 3293.59, "duration": 3.82}, {"text": "So that's what this is.", "start": 3297.41, "duration": 2.72}, {"text": "Turns out, you\nkeep your NAD/NADH", "start": 3300.13, "duration": 2.61}, {"text": "to largely favor the oxidation\nreactions you want to do.", "start": 3302.74, "duration": 4.2}, {"text": "And let's create a different\ncurrency for reduction.", "start": 3306.94, "duration": 3.63}, {"text": "And this currency ends up\nbeing a different molecule,", "start": 3310.57, "duration": 3.756}, {"text": "NADPH/NADP+.", "start": 3314.326, "duration": 0.974}, {"text": "And you use this as a\ncofactor pair for reduction.", "start": 3318.22, "duration": 6.195}, {"text": "Well, what is NADPH?", "start": 3324.415, "duration": 1.965}, {"text": "Well, it's effectively\nthe same thing as NADH.", "start": 3329.51, "duration": 4.62}, {"text": "But now you mark it\nas a separate pool", "start": 3334.13, "duration": 2.64}, {"text": "with a two prime phosphate\non the ADP portion", "start": 3336.77, "duration": 5.52}, {"text": "of the molecule.", "start": 3342.29, "duration": 1.475}, {"text": "Let me draw it out for you.", "start": 3343.765, "duration": 1.125}, {"text": "OK.", "start": 3386.47, "duration": 0.54}, {"text": "So this here is NA--", "start": 3387.01, "duration": 3.39}, {"text": "so if I took this phosphate\noff, this would be NADH,", "start": 3390.4, "duration": 4.2}, {"text": "put a two prime\nphosphate on, now I", "start": 3394.6, "duration": 2.88}, {"text": "mark this as a separate\nmolecule pool, NADPH.", "start": 3397.48, "duration": 4.02}, {"text": "A is an adenine.", "start": 3409.409, "duration": 1.191}, {"text": "Remember, it's a nicotinamide\nadenine dinucleoside.", "start": 3410.6, "duration": 4.03}, {"text": "OK?", "start": 3414.63, "duration": 0.5}, {"text": "So here's a adenine, phosphate,\nphosphate, other nucleoside", "start": 3415.13, "duration": 4.38}, {"text": "with the nicotinamide group.", "start": 3419.51, "duration": 1.59}, {"text": "This here is in\nthe reduced form.", "start": 3421.1, "duration": 2.79}, {"text": "Seen this now a\nmillion times, but we", "start": 3427.48, "duration": 4.52}, {"text": "can oxidize it as possible.", "start": 3432.0, "duration": 2.76}, {"text": "That generates this two\nelectron hydride ion.", "start": 3434.76, "duration": 4.52}, {"text": "So remove two electrons and now\nthis nicotinamide form is here", "start": 3439.28, "duration": 16.22}, {"text": "in the NADP+ or oxidized\nform of the molecule.", "start": 3455.5, "duration": 10.36}, {"text": "And so effectively by marking\nthis as a separate pool with", "start": 3465.86, "duration": 3.44}, {"text": "that two prime phosphate, you\ncan have a different NADH/NAD+", "start": 3469.3, "duration": 6.0}, {"text": "ratio in cells.", "start": 3475.3, "duration": 1.44}, {"text": "Then you have NADH/NADP+\nplus ratio and cells.", "start": 3476.74, "duration": 5.13}, {"text": "Use one co-factor\nfair pair to favor", "start": 3481.87, "duration": 2.64}, {"text": "oxidation and the\nother co-factor pair", "start": 3484.51, "duration": 2.88}, {"text": "to favor reduction.", "start": 3487.39, "duration": 3.1}, {"text": "And so I want to give\na quick aside on NADPH", "start": 3490.49, "duration": 3.99}, {"text": "because it's really\nalso NADPH that", "start": 3494.48, "duration": 3.03}, {"text": "can be very important in keeping\nthe cytosol of cells reduced.", "start": 3497.51, "duration": 5.13}, {"text": "So what do I mean by that?", "start": 3502.64, "duration": 1.26}, {"text": "Well, you remember you\nlearned from Professor Yaffe.", "start": 3503.9, "duration": 3.47}, {"text": "We talked about proteins\nthat you can have", "start": 3507.37, "duration": 3.16}, {"text": "these inside the side cytosol.", "start": 3510.53, "duration": 2.37}, {"text": "You'd have your cystine\nresidues on proteins", "start": 3512.9, "duration": 3.27}, {"text": "be in this reduced form.", "start": 3516.17, "duration": 2.31}, {"text": "And outside the cell, you'd form\nthese disulfide bonds, which", "start": 3518.48, "duration": 4.47}, {"text": "is basically oxidized cystine.", "start": 3522.95, "duration": 2.49}, {"text": "And so in the cytosol, you want\nyour cystine residues reduced.", "start": 3525.44, "duration": 4.71}, {"text": "And outside of the\ncell, you end up", "start": 3530.15, "duration": 1.95}, {"text": "with these disulfide\nbonds on proteins.", "start": 3532.1, "duration": 4.28}, {"text": "Why does cystine tend to get\noxidized outside the cell?", "start": 3536.38, "duration": 4.95}, {"text": "Well, there's lots of\noxygen in our atmosphere.", "start": 3541.33, "duration": 3.09}, {"text": "Oxygen's a good\nelectron acceptor.", "start": 3544.42, "duration": 2.16}, {"text": "It's very good at oxidation.", "start": 3546.58, "duration": 2.07}, {"text": "In fact, that's what gives\nit this property that makes", "start": 3548.65, "duration": 3.45}, {"text": "oxidative phosphorylation work.", "start": 3552.1, "duration": 2.31}, {"text": "And so it turns out\nthat these cystines,", "start": 3554.41, "duration": 3.12}, {"text": "these sulfhydryl groups, like to\ngive their electrons to oxygen.", "start": 3557.53, "duration": 3.36}, {"text": "And that leads to these\nmore oxidized things", "start": 3560.89, "duration": 3.21}, {"text": "outside the cell.", "start": 3564.1, "duration": 1.66}, {"text": "In fact, oxygen is very\ngood at accepting electrons", "start": 3565.76, "duration": 3.2}, {"text": "from lots of donors.", "start": 3568.96, "duration": 1.98}, {"text": "So if you have iron 2+ sitting\naround outside the cell,", "start": 3570.94, "duration": 4.8}, {"text": "oxygen is very good at oxidizing\nthat iron 2+ to iron 3+.", "start": 3575.74, "duration": 6.21}, {"text": "That's rust.", "start": 3581.95, "duration": 1.89}, {"text": "And this process, in the end,\nends up transferring electrons", "start": 3583.84, "duration": 4.29}, {"text": "to oxygen and can generate\nlots of oxygen species,", "start": 3588.13, "duration": 4.72}, {"text": "including oxygen radicals.", "start": 3592.85, "duration": 1.98}, {"text": "And so you can get things\nlike this O2- superoxide,", "start": 3594.83, "duration": 5.17}, {"text": "ultimately hydrogen\nperoxide, also", "start": 3600.0, "duration": 11.17}, {"text": "comes from oxygen\npicking up electrons.", "start": 3611.17, "duration": 4.21}, {"text": "And as you know, very\nreactive molecules like this", "start": 3615.38, "duration": 3.71}, {"text": "can damage membranes,\ndamage proteins, kill cells.", "start": 3619.09, "duration": 4.29}, {"text": "What do we use hydrogen\nperoxide for in daily life?", "start": 3623.38, "duration": 2.55}, {"text": "Use it to clean wounds,\nkills a bunch of bacteria.", "start": 3625.93, "duration": 3.15}, {"text": "And ultimately, production\nof these so-called ROS,", "start": 3629.08, "duration": 5.82}, {"text": "or reactive oxygen\nspecies, in excess", "start": 3634.9, "duration": 7.36}, {"text": "can be very bad for\nbiological systems.", "start": 3642.26, "duration": 2.91}, {"text": "And this is one of\nthe arguments for why", "start": 3645.17, "duration": 2.13}, {"text": "antioxidants are good for us.", "start": 3647.3, "duration": 1.56}, {"text": "They protect us and ourselves\nfrom these reactive oxygen", "start": 3648.86, "duration": 5.04}, {"text": "species.", "start": 3653.9, "duration": 2.04}, {"text": "OK.", "start": 3655.94, "duration": 1.02}, {"text": "Now, cells, of course,\nhave endogenous ways", "start": 3656.96, "duration": 3.3}, {"text": "to deal with this, to keep\ncystines in our cytosol", "start": 3660.26, "duration": 3.3}, {"text": "reduced, to keep our cytosol\nin this reducing environment,", "start": 3663.56, "duration": 2.88}, {"text": "prevent this ROS damage.", "start": 3666.44, "duration": 2.76}, {"text": "And really, if\nyou're going to have", "start": 3669.2, "duration": 2.28}, {"text": "things to deal with these\nreactive molecules, what do", "start": 3671.48, "duration": 2.28}, {"text": "you want?", "start": 3673.76, "duration": 0.42}, {"text": "Well, you want\nsomething that's going", "start": 3674.18, "duration": 1.542}, {"text": "to buffer the damage that\nthese things can cause.", "start": 3675.722, "duration": 4.241}, {"text": "That is, if these\nthings are going", "start": 3679.963, "duration": 1.417}, {"text": "to react with lipids and\nproteins and cause damage", "start": 3681.38, "duration": 3.42}, {"text": "and you want to keep\nthe cytosol reduced,", "start": 3684.8, "duration": 1.71}, {"text": "you really want to have\na series of molecules", "start": 3686.51, "duration": 2.01}, {"text": "that will actually, instead,\nundergo this process before it", "start": 3688.52, "duration": 4.53}, {"text": "can damage critical\nstructures in the cell.", "start": 3693.05, "duration": 2.79}, {"text": "And a key system cells\nuse to do this is", "start": 3695.84, "duration": 2.43}, {"text": "something called glutathione.", "start": 3698.27, "duration": 3.75}, {"text": "So what is glutathione?", "start": 3702.02, "duration": 2.1}, {"text": "Well, glutathione is a\nsmall molecule tripeptide.", "start": 3704.12, "duration": 4.36}, {"text": "All right?", "start": 3708.48, "duration": 0.5}, {"text": "And it's among the most abundant\nsmall molecules found in cells.", "start": 3708.98, "duration": 5.34}, {"text": "And effectively,\nwhat glutathione does", "start": 3714.32, "duration": 2.16}, {"text": "is it serves this purpose\nof reacting with nasty stuff", "start": 3716.48, "duration": 4.2}, {"text": "before it can damage other\nbiomolecules and hurt the cell.", "start": 3720.68, "duration": 5.85}, {"text": "And so by tripeptide,\nwhat it is is it's", "start": 3726.53, "duration": 2.91}, {"text": "a tripeptide of glutamate\nwith a gamma peptide bond", "start": 3729.44, "duration": 5.37}, {"text": "to glycine and then cystine--", "start": 3734.81, "duration": 1.98}, {"text": "so glutamate glycine\ncystine tripeptide", "start": 3736.79, "duration": 4.11}, {"text": "that looks like this.", "start": 3740.9, "duration": 1.29}, {"text": "OK.", "start": 3758.17, "duration": 0.5}, {"text": "So this here is the\namino acid glutamate.", "start": 3758.67, "duration": 4.85}, {"text": "Here's the alpha carbon\nwith the carboxylic acid", "start": 3763.52, "duration": 5.082}, {"text": "and amine groups.", "start": 3768.602, "duration": 0.708}, {"text": "So you would typically think of\nthe peptide bond of glutamate", "start": 3769.31, "duration": 3.18}, {"text": "was in a chain as being\nfrom this nitrogen", "start": 3772.49, "duration": 3.42}, {"text": "to the next amino acid and that\ncarbon to the next amino acid.", "start": 3775.91, "duration": 3.57}, {"text": "But in this case, it uses the\nnitrogen on the side chain,", "start": 3779.48, "duration": 3.73}, {"text": "the so-called\ngamma linkage here,", "start": 3783.21, "duration": 3.35}, {"text": "to form a peptide bond with--", "start": 3786.56, "duration": 2.82}, {"text": "oops, sorry.", "start": 3792.43, "duration": 2.97}, {"text": "This would be glutamic acid.", "start": 3795.4, "duration": 2.22}, {"text": "It uses this gamma\ncarboxylic acid", "start": 3797.62, "duration": 2.79}, {"text": "on the side chain of glutamate\nto form a peptide bond", "start": 3800.41, "duration": 6.38}, {"text": "with glycine.", "start": 3806.79, "duration": 3.0}, {"text": "OK.", "start": 3813.22, "duration": 0.96}, {"text": "So this is glutamate.", "start": 3814.18, "duration": 5.03}, {"text": "This is glycine.", "start": 3819.21, "duration": 2.52}, {"text": "And then this has a\npeptide bond to cystine,", "start": 3821.73, "duration": 18.01}, {"text": "which contributes that\nsulfhydryl group that", "start": 3839.74, "duration": 3.87}, {"text": "can either exist in\nthis reduced form.", "start": 3843.61, "duration": 4.11}, {"text": "Or, if there's two\nof them together,", "start": 3847.72, "duration": 7.06}, {"text": "you can go into\nthis oxidized form.", "start": 3854.78, "duration": 3.56}, {"text": "And so, often, this is drawn as\nglutathione GSH in the reduced", "start": 3858.34, "duration": 6.99}, {"text": "form.", "start": 3865.33, "duration": 1.12}, {"text": "And if you have two glutathione\nmolecules that then basically", "start": 3866.45, "duration": 5.81}, {"text": "form a disulfide bond\nto give you this GSSG", "start": 3872.26, "duration": 4.89}, {"text": "oxidized form of the molecule.", "start": 3877.15, "duration": 3.9}, {"text": "And NADPH plays a\nkey role in the cell,", "start": 3881.05, "duration": 4.38}, {"text": "because that's an\noxidation reduction", "start": 3885.43, "duration": 1.56}, {"text": "reaction in keeping glutathione\nin the reduced form.", "start": 3886.99, "duration": 3.81}, {"text": "So if you have two\nGSH molecules that", "start": 3890.8, "duration": 4.68}, {"text": "can cycle to a oxidized GSSG--", "start": 3895.48, "duration": 4.59}, {"text": "so this is reduced,\nthis is oxidized.", "start": 3900.07, "duration": 6.16}, {"text": "On the other side you can\ncycle those electrons.", "start": 3906.23, "duration": 3.65}, {"text": "If something gets\noxidized, something else", "start": 3909.88, "duration": 1.75}, {"text": "has to be reduced.", "start": 3911.63, "duration": 1.63}, {"text": "So you can have NADP+ and NADPH.", "start": 3913.26, "duration": 5.15}, {"text": "This is reduced.", "start": 3923.65, "duration": 3.01}, {"text": "This is oxidized.", "start": 3926.66, "duration": 1.44}, {"text": "And so by maintaining a\nhigh ratio of NADH to NADP+,", "start": 3928.1, "duration": 6.54}, {"text": "you can keep a high ratio of\nreduced to oxidize glutathione", "start": 3934.64, "duration": 4.95}, {"text": "in the cell and keep the\ncell in a protected reducing", "start": 3939.59, "duration": 4.44}, {"text": "environment where you have these\nglutathione molecules to react", "start": 3944.03, "duration": 5.19}, {"text": "with other things before it\ncauses damage to the cell.", "start": 3949.22, "duration": 4.41}, {"text": "All right.", "start": 3953.63, "duration": 0.88}, {"text": "A little bit of a diversion,\nbut a very important system", "start": 3954.51, "duration": 3.74}, {"text": "that cells use related to\noxidation reduction and NADPH,", "start": 3958.25, "duration": 4.47}, {"text": "and needed a place to talk about\nit somewhere in the course.", "start": 3962.72, "duration": 3.7}, {"text": "All right.", "start": 3966.42, "duration": 0.5}, {"text": "Now back to photosynthesis.", "start": 3966.92, "duration": 3.52}, {"text": "Now, for photosynthesis,\nthis reduced", "start": 3970.44, "duration": 3.65}, {"text": "NADPH molecule's\nof course useful,", "start": 3974.09, "duration": 2.91}, {"text": "because it can serve as\na source of electrons", "start": 3977.0, "duration": 2.97}, {"text": "to donate carbons to reduce CO2.", "start": 3979.97, "duration": 3.69}, {"text": "So if you're going to reduce\nCO2 to make carbohydrate or fat,", "start": 3983.66, "duration": 5.67}, {"text": "you need this\nsource of electrons.", "start": 3989.33, "duration": 1.53}, {"text": "Those can come from NADPH,\nwhich can be oxidized to NADP+.", "start": 3990.86, "duration": 7.16}, {"text": "And so perhaps at\nthis point, you've", "start": 3998.02, "duration": 2.1}, {"text": "already guessed or\nmaybe already know", "start": 4000.12, "duration": 1.92}, {"text": "that photosynthesis uses the\nfavorable electron transfer", "start": 4002.04, "duration": 6.3}, {"text": "from water to generate NADPH.", "start": 4008.34, "duration": 4.35}, {"text": "And to do that, you use\nthe energy of the sun.", "start": 4012.69, "duration": 3.85}, {"text": "Now, of course, if you're going\nto do a favorable electron", "start": 4016.54, "duration": 4.22}, {"text": "transfer, that can be coupled,\njust like we talked about", "start": 4020.76, "duration": 5.46}, {"text": "for oxidative phosphorylation,\nto make delta psi/delta pH.", "start": 4026.22, "duration": 6.42}, {"text": "And if we can use that\nfavorable electron transfer", "start": 4032.64, "duration": 2.91}, {"text": "to make delta psi/delta\npH, we can also", "start": 4035.55, "duration": 2.91}, {"text": "use it to do other work,\nincluding making ATP exactly", "start": 4038.46, "duration": 5.46}, {"text": "as we described for\noxidative phosphorylation.", "start": 4043.92, "duration": 4.62}, {"text": "And at the highest level, this\nis exactly how photosynthesis", "start": 4048.54, "duration": 3.96}, {"text": "traps solar energy\nand uses that energy", "start": 4052.5, "duration": 3.42}, {"text": "to both remake reduced\ncarbon and generates", "start": 4055.92, "duration": 5.9}, {"text": "a battery for the\nphotosynthetic organism that", "start": 4061.82, "duration": 3.15}, {"text": "can be used to make\nATP or do other work,", "start": 4064.97, "duration": 3.42}, {"text": "provided that sun is available.", "start": 4068.39, "duration": 4.02}, {"text": "And so classically,\nphotosynthesis", "start": 4072.41, "duration": 3.36}, {"text": "can really be separated into, I\nguess, two distinct processes.", "start": 4075.77, "duration": 4.32}, {"text": "All right?", "start": 4080.09, "duration": 0.85}, {"text": "So you have this process\nof taking solar energy,", "start": 4080.94, "duration": 8.3}, {"text": "using that solar\nenergy to charge up", "start": 4089.24, "duration": 4.44}, {"text": "a battery, delta psi/delta pH,\nwhich of course can be used", "start": 4093.68, "duration": 4.53}, {"text": "to generate ATP or do other\nwork, and at the same time", "start": 4098.21, "duration": 4.41}, {"text": "gives you an electron\ndonor, NADPH,", "start": 4102.62, "duration": 5.01}, {"text": "that is useful to\ngenerate reduced carbon.", "start": 4107.63, "duration": 4.38}, {"text": "Once you generate, high ATP/ADP\nratio, high NADPH/NADP ratio.", "start": 4112.01, "duration": 8.309}, {"text": "Now we can use that to\nbe couple to do something", "start": 4120.319, "duration": 4.801}, {"text": "else unfavorable.", "start": 4125.12, "duration": 2.25}, {"text": "And that would be\nsomething like reduced CO2", "start": 4127.37, "duration": 4.5}, {"text": "to generate a carbohydrate.", "start": 4131.87, "duration": 2.13}, {"text": "And typically, when we\ntalk about photosynthesis,", "start": 4137.31, "duration": 3.27}, {"text": "the way it's often\ndescribed is how you", "start": 4140.58, "duration": 1.77}, {"text": "reduced CO2 to carbohydrate.", "start": 4142.35, "duration": 1.86}, {"text": "And we'll do that too.", "start": 4144.21, "duration": 1.26}, {"text": "But of course, we'll then see\nonce you have carbohydrates,", "start": 4145.47, "duration": 3.929}, {"text": "obviously, it's just\nfurther reduction of carbon", "start": 4149.399, "duration": 2.401}, {"text": "to make fatty acids and lipids.", "start": 4151.8, "duration": 4.769}, {"text": "We'll discuss later\nhow we can use", "start": 4156.569, "duration": 1.891}, {"text": "those to make amino\nacids, which would", "start": 4158.46, "duration": 1.649}, {"text": "allow you to make proteins.", "start": 4160.109, "duration": 1.691}, {"text": "And, of course, we can also\nstore those carbohydrates", "start": 4161.8, "duration": 7.09}, {"text": "as disaccharides or\npolysaccharides, storage", "start": 4168.89, "duration": 4.03}, {"text": "sugars, which is what plants do.", "start": 4172.92, "duration": 2.22}, {"text": "They make starch, they\nmake sucrose, et cetera,", "start": 4175.14, "duration": 2.79}, {"text": "as a way to store\nthat reduce carbon", "start": 4177.93, "duration": 3.299}, {"text": "so that they can have\na source of energy,", "start": 4181.229, "duration": 3.21}, {"text": "do the oxidation reactions, to\ndeal with their energetic needs", "start": 4184.439, "duration": 3.511}, {"text": "when the sun is not shining.", "start": 4187.95, "duration": 2.76}, {"text": "All right.", "start": 4190.71, "duration": 1.479}, {"text": "So let's break down\nthese two processes.", "start": 4192.189, "duration": 5.961}, {"text": "And so to just be very\nexplicit, the first part", "start": 4198.15, "duration": 3.36}, {"text": "is basically trapping\nenergy to make a battery.", "start": 4201.51, "duration": 4.89}, {"text": "All right?", "start": 4206.4, "duration": 1.14}, {"text": "And so this means that we need\nto generate delta psi/delta", "start": 4207.54, "duration": 4.29}, {"text": "pH via favorable electron\ntransport, exactly what we", "start": 4211.83, "duration": 4.98}, {"text": "describe for OXPHOS.", "start": 4216.81, "duration": 1.15}, {"text": "But, of course,\nphotosynthesis was first.", "start": 4217.96, "duration": 2.24}, {"text": "This would then allow us to use\nATP to fill our energy needs.", "start": 4220.2, "duration": 3.24}, {"text": "And we get NADPH if we set it\nup in the right way, which is", "start": 4223.44, "duration": 4.11}, {"text": "important for carbon reduction.", "start": 4227.55, "duration": 2.81}, {"text": "Then we need to use NADPH\nand ATP via pathways", "start": 4230.36, "duration": 3.81}, {"text": "to describe how we can use that\nto reduce CO2, and ultimately", "start": 4234.17, "duration": 4.2}, {"text": "produce glucose, which allows\nus to store energy for later.", "start": 4238.37, "duration": 4.57}, {"text": "All right.", "start": 4242.94, "duration": 0.5}, {"text": "So that is, at a very high\nlevel, what photosynthesis is.", "start": 4243.44, "duration": 3.45}, {"text": "And, of course, this\noccurs in plants.", "start": 4246.89, "duration": 3.21}, {"text": "All right?", "start": 4250.1, "duration": 1.63}, {"text": "But perhaps more\nimportantly, it also", "start": 4251.73, "duration": 1.95}, {"text": "occurs in algae and other\nunicellular eukaryotes", "start": 4253.68, "duration": 16.51}, {"text": "as well as in prokaryotes--\nphotosynthetic prokaryotes,", "start": 4270.19, "duration": 7.48}, {"text": "bacteria.", "start": 4277.67, "duration": 1.38}, {"text": "And, of course,\nphotosynthetic bacteria,", "start": 4279.05, "duration": 2.82}, {"text": "unicellular eukaryotes, algae--", "start": 4281.87, "duration": 2.34}, {"text": "these really are\nthe heroes of life.", "start": 4284.21, "duration": 2.68}, {"text": "These are the things that life\nstarted from, and generated", "start": 4286.89, "duration": 3.56}, {"text": "the oxygenated\natmosphere, and ultimately", "start": 4290.45, "duration": 2.22}, {"text": "led to the evolution\nof higher plants,", "start": 4292.67, "duration": 2.61}, {"text": "but also enabled the\nformation of animal life,", "start": 4295.28, "duration": 4.38}, {"text": "and really anything that lives\noff of eating other organisms.", "start": 4299.66, "duration": 5.22}, {"text": "Just a few facts\nabout photosynthesis", "start": 4304.88, "duration": 2.73}, {"text": "because it's really quite\nan amazing process--", "start": 4307.61, "duration": 3.7}, {"text": "and so about 10 to the\n17th kilojoules, at least", "start": 4311.31, "duration": 5.54}, {"text": "by some estimate, of energy\nis harvested on our planet", "start": 4316.85, "duration": 7.88}, {"text": "from photosynthesis every year.", "start": 4324.73, "duration": 2.67}, {"text": "Just to give you a perspective\nof what that number means,", "start": 4327.4, "duration": 2.55}, {"text": "that is 10 times the\nworldwide energy use", "start": 4329.95, "duration": 4.23}, {"text": "by all people on Earth.", "start": 4334.18, "duration": 1.35}, {"text": "So if you add up all the\nenergy that we as humans use", "start": 4335.53, "duration": 3.15}, {"text": "in the world, it is tenfold\nless than the amount of energy", "start": 4338.68, "duration": 4.53}, {"text": "that is harvested\nby photosynthesis,", "start": 4343.21, "duration": 4.42}, {"text": "by photosynthetic\norganisms around the world.", "start": 4347.63, "duration": 4.09}, {"text": "Photosynthetic organisms, when\nthey do this, consume CO2.", "start": 4351.72, "duration": 4.83}, {"text": "All right?", "start": 4356.55, "duration": 0.78}, {"text": "So that is removing\nCO2, the greenhouse", "start": 4357.33, "duration": 2.73}, {"text": "gas from our atmosphere.", "start": 4360.06, "duration": 3.76}, {"text": "And this occurs on\na massive scale.", "start": 4363.82, "duration": 3.15}, {"text": "So this is better than any\nman-made engineering solution", "start": 4366.97, "duration": 4.73}, {"text": "that we have come\nup with by far.", "start": 4371.7, "duration": 3.34}, {"text": "And I think this\nreally illustrates", "start": 4375.04, "duration": 3.06}, {"text": "the awesome power\nof biology to solve", "start": 4378.1, "duration": 3.54}, {"text": "some of the biggest problems\nthat face our society today.", "start": 4381.64, "duration": 4.15}, {"text": "So world energy problems--", "start": 4385.79, "duration": 3.14}, {"text": "photosynthesis harnesses\na ton of energy.", "start": 4388.93, "duration": 7.32}, {"text": "Global warming,\ngreenhouse gases--", "start": 4396.25, "duration": 1.98}, {"text": "photosynthesis, better\nthan almost anything", "start": 4398.23, "duration": 2.76}, {"text": "at dealing with these\nCO2 that is produced.", "start": 4400.99, "duration": 5.2}, {"text": "However, this also illustrates\nwhat some of the problems are", "start": 4406.19, "duration": 5.377}, {"text": "and what some of the issues\nare with fossil fuels,", "start": 4411.567, "duration": 2.083}, {"text": "because what are fossil fuels.", "start": 4413.65, "duration": 1.95}, {"text": "Well, they're\neffectively reduced", "start": 4415.6, "duration": 2.19}, {"text": "carbon that is trapped in\nthe ground somewhere, that is", "start": 4417.79, "duration": 4.11}, {"text": "effectively old photosynthesis.", "start": 4421.9, "duration": 2.53}, {"text": "So these are organisms in many,\nmany, many, many years ago", "start": 4424.43, "duration": 5.57}, {"text": "that did photosynthesis,\nmade reduced carbon that", "start": 4430.0, "duration": 3.75}, {"text": "was effectively\ntrapped in the ground.", "start": 4433.75, "duration": 2.73}, {"text": "And so the fact that\nphotosynthesis transducers 10", "start": 4436.48, "duration": 5.49}, {"text": "to 17th kilojoules of energy\nper year and we're using 1/10", "start": 4441.97, "duration": 4.41}, {"text": "of that amount of energy, if\nthat's all coming from fossil", "start": 4446.38, "duration": 3.24}, {"text": "fuels, that means we're\nusing 1/10 of a year's worth", "start": 4449.62, "duration": 4.17}, {"text": "of photosynthesis--\nand, of course,", "start": 4453.79, "duration": 1.68}, {"text": "a year is not entirely\nstored in the ground--", "start": 4455.47, "duration": 2.82}, {"text": "per year.", "start": 4458.29, "duration": 0.69}, {"text": "So that's a lot of energy.", "start": 4458.98, "duration": 1.26}, {"text": "And it really comes down to why\npeople say fossil fuels can't", "start": 4460.24, "duration": 4.47}, {"text": "last forever, and also why the\nnet release of these things", "start": 4464.71, "duration": 6.18}, {"text": "can change our atmosphere,\nbecause, of course,", "start": 4470.89, "duration": 2.67}, {"text": "once upon a time, there was\nmuch more CO2 in the atmosphere.", "start": 4473.56, "duration": 3.81}, {"text": "And photosynthesis,\nover millennia,", "start": 4477.37, "duration": 2.52}, {"text": "trapping these things\nas fossil fuels really", "start": 4479.89, "duration": 3.09}, {"text": "has lowered CO2 in our\natmosphere to the levels", "start": 4482.98, "duration": 3.66}, {"text": "that they exist today,\nand how, basically,", "start": 4486.64, "duration": 4.68}, {"text": "burning fossil fuels on\nthe scale that we are", "start": 4491.32, "duration": 3.63}, {"text": "is able to change\nour atmosphere.", "start": 4494.95, "duration": 4.42}, {"text": "So you can view this both\nas glass half full and glass", "start": 4499.37, "duration": 2.51}, {"text": "half empty.", "start": 4501.88, "duration": 1.2}, {"text": "It really says\nunderstanding photosynthesis", "start": 4503.08, "duration": 2.25}, {"text": "could be a key to solving\nsome of these problems.", "start": 4505.33, "duration": 3.1}, {"text": "But it also points out\nwhy some of these things", "start": 4508.43, "duration": 3.35}, {"text": "might be problems to begin with.", "start": 4511.78, "duration": 2.42}, {"text": "All right.", "start": 4514.2, "duration": 1.11}, {"text": "Now we want to discuss first\nhow photosynthesis traps energy.", "start": 4515.31, "duration": 5.07}, {"text": "And you'll see that it\nis similar to oxidative", "start": 4520.38, "duration": 3.81}, {"text": "phosphorylation in\nmany, many ways.", "start": 4524.19, "duration": 4.87}, {"text": "So it's going to\noccur at a membrane.", "start": 4529.06, "duration": 4.37}, {"text": "All right?", "start": 4533.43, "duration": 1.82}, {"text": "It's going to involve a\nseries of protein complexes", "start": 4535.25, "duration": 8.97}, {"text": "where we're going\nto favor, we're", "start": 4544.22, "duration": 2.37}, {"text": "going to couple\nfavorable electron", "start": 4546.59, "duration": 2.73}, {"text": "transport along a\nelectron transport chain", "start": 4549.32, "duration": 4.44}, {"text": "to favor proton pumping.", "start": 4553.76, "duration": 2.91}, {"text": "That is going to generate\na membrane potential delta", "start": 4556.67, "duration": 5.06}, {"text": "psi/delta pH.", "start": 4561.73, "duration": 0.76}, {"text": "In order to do\nthat, of course, we", "start": 4565.21, "duration": 1.98}, {"text": "need favorable\nelectron transport", "start": 4567.19, "duration": 2.37}, {"text": "from something that is\nlower standard reduction", "start": 4569.56, "duration": 4.8}, {"text": "potential to something that\nis higher standard reduction", "start": 4574.36, "duration": 3.99}, {"text": "potential.", "start": 4578.35, "duration": 0.54}, {"text": "That is what is going\nto make it favorable,", "start": 4578.89, "duration": 2.31}, {"text": "allow proton pumping.", "start": 4581.2, "duration": 2.85}, {"text": "That, when it generates\ndelta psi/delta pH,", "start": 4584.05, "duration": 4.32}, {"text": "we can now harness that\nas a way to synthesize", "start": 4588.37, "duration": 7.19}, {"text": "ATP or do other work, as\nwe've now talked about a lot.", "start": 4595.56, "duration": 6.736}, {"text": "Looks a lot like\noxidative phosphorylation", "start": 4602.296, "duration": 1.75}, {"text": "and it makes sense.", "start": 4604.046, "duration": 1.304}, {"text": "Oxidative phosphorylation\ncame from photosynthesis.", "start": 4605.35, "duration": 4.11}, {"text": "However, there are some\nreally big differences", "start": 4609.46, "duration": 3.09}, {"text": "between the two.", "start": 4612.55, "duration": 1.47}, {"text": "And that is in photosynthesis,\nas I've already alluded", "start": 4614.02, "duration": 3.24}, {"text": "to, the electron donor\nis going to be water,", "start": 4617.26, "duration": 6.45}, {"text": "which will generate oxygen. And\nthe electron acceptor is NADP+,", "start": 4623.71, "duration": 8.25}, {"text": "which will generate NADPH.", "start": 4631.96, "duration": 2.75}, {"text": "And you might now be\nasking, well, how on Earth", "start": 4639.23, "duration": 2.85}, {"text": "can this be possible?", "start": 4642.08, "duration": 1.71}, {"text": "Because, remember, the standard\nreduction potential of NADH", "start": 4643.79, "duration": 10.04}, {"text": "is less than the standard\nreduction potential", "start": 4653.83, "duration": 4.8}, {"text": "of our oxygen water pair.", "start": 4658.63, "duration": 3.69}, {"text": "And it's really this\nthat makes the change", "start": 4662.32, "duration": 4.11}, {"text": "in standard reduction\npotential positive, which", "start": 4666.43, "duration": 3.15}, {"text": "means that delta G is\ngoing to be negative,", "start": 4669.58, "duration": 4.21}, {"text": "which is why electron\ntransport and oxidative", "start": 4673.79, "duration": 2.36}, {"text": "phosphorylation is\nfavorable and can be coupled", "start": 4676.15, "duration": 2.55}, {"text": "to make delta psi/delta pH.", "start": 4678.7, "duration": 3.81}, {"text": "Now, adding a\nphosphate to NAD/NADH", "start": 4682.51, "duration": 4.29}, {"text": "does not change its\nstandard reduction potential", "start": 4686.8, "duration": 3.0}, {"text": "in a way that is at all\nmeaningful to impact", "start": 4689.8, "duration": 3.18}, {"text": "what goes on.", "start": 4692.98, "duration": 1.29}, {"text": "And so this is really where\nenergy input from the sun", "start": 4694.27, "duration": 5.43}, {"text": "becomes critical.", "start": 4699.7, "duration": 1.71}, {"text": "And that is-- it is this light\nenergy from a photon that", "start": 4701.41, "duration": 7.23}, {"text": "in the end makes water\na good electron donor,", "start": 4708.64, "duration": 4.18}, {"text": "such that all of these other\nthings are satisfied that", "start": 4712.82, "duration": 4.1}, {"text": "electron transport is favorable\ngoing from lower to higher", "start": 4716.92, "duration": 4.26}, {"text": "standard reduction potential\nwith NADP+ ultimately being", "start": 4721.18, "duration": 5.91}, {"text": "the final electron acceptor,\nsuch that the change", "start": 4727.09, "duration": 4.5}, {"text": "in standard production\npotential is positive.", "start": 4731.59, "duration": 3.75}, {"text": "And that really is the\nmagic of photosynthesis.", "start": 4735.34, "duration": 5.045}, {"text": "And, of course,\nonce you do that,", "start": 4740.385, "duration": 1.375}, {"text": "now you have delta psi/delta pH.", "start": 4741.76, "duration": 2.07}, {"text": "You can use that to\nmake ATP, do other work", "start": 4743.83, "duration": 2.37}, {"text": "for the photosynthetic organism.", "start": 4746.2, "duration": 1.86}, {"text": "And you also get NADPH,\nwhich is an electron", "start": 4748.06, "duration": 2.31}, {"text": "donor for carbon reduction.", "start": 4750.37, "duration": 2.43}, {"text": "And the net result is that\nyou get this familiar formula", "start": 4752.8, "duration": 6.57}, {"text": "that you learned in grade\nschool for photosynthesis--", "start": 4759.37, "duration": 2.97}, {"text": "CO2 plus water with light goes\nto oxygen plus carbohydrate,", "start": 4762.34, "duration": 9.95}, {"text": "which is, of course, the\nexact opposite of combustion.", "start": 4772.29, "duration": 5.51}, {"text": "We talked a lot about how\nburning wood combustion is", "start": 4777.8, "duration": 5.94}, {"text": "the opposite reaction that's\nfavorable-- lots of energy", "start": 4783.74, "duration": 2.97}, {"text": "released.", "start": 4786.71, "duration": 1.42}, {"text": "And so the energy\ninput here is obviously", "start": 4788.13, "duration": 4.52}, {"text": "the opposite of that to do\nthis opposite of combustion", "start": 4792.65, "duration": 5.79}, {"text": "and stores lots of energy.", "start": 4798.44, "duration": 2.07}, {"text": "All right, so again,\nI want to say why", "start": 4800.51, "duration": 5.32}, {"text": "use water as an electron donor?", "start": 4805.83, "duration": 3.09}, {"text": "Well, because it's abundant.", "start": 4808.92, "duration": 1.26}, {"text": "There's nothing particularly\nspecial about water other", "start": 4810.18, "duration": 3.18}, {"text": "than its abundance, just like\nwe talked about in oxygen is not", "start": 4813.36, "duration": 4.71}, {"text": "really being special\nother than that it's", "start": 4818.07, "duration": 1.92}, {"text": "a good electron\nacceptor and abundant.", "start": 4819.99, "duration": 3.18}, {"text": "You could obviously build\nsystems that do something other", "start": 4823.17, "duration": 3.21}, {"text": "than oxygen and water.", "start": 4826.38, "duration": 2.29}, {"text": "And so there are\nextremophiles out there", "start": 4828.67, "duration": 2.33}, {"text": "that instead do\nhydrogen sulfide to make", "start": 4831.0, "duration": 6.36}, {"text": "reduced sulfur as another--", "start": 4837.36, "duration": 2.78}, {"text": "sorry, oxidize sulfur as a\nway of doing photosynthesis.", "start": 4842.9, "duration": 6.57}, {"text": "Exact same concepts\nwould apply is what", "start": 4849.47, "duration": 2.7}, {"text": "we're going to talk about here.", "start": 4852.17, "duration": 2.97}, {"text": "All right.", "start": 4855.14, "duration": 0.51}, {"text": "Now, the parts of\nphotosynthesis,", "start": 4855.65, "duration": 4.8}, {"text": "as you might guess,\nare spatially distinct.", "start": 4860.45, "duration": 3.43}, {"text": "That is, we're going to generate\ndelta psi/delta pH and NADPH.", "start": 4863.88, "duration": 9.02}, {"text": "Those are basically\nthis electron", "start": 4872.9, "duration": 2.79}, {"text": "transport chain reactions,\ncharge the battery, et cetera.", "start": 4875.69, "duration": 4.27}, {"text": "And then imagine if we're going\nto fix CO2 as carbohydrate.", "start": 4879.96, "duration": 10.12}, {"text": "Well, effectively that's more\nlike what we talked about", "start": 4890.08, "duration": 2.4}, {"text": "with gluconeogenesis.", "start": 4892.48, "duration": 1.65}, {"text": "That's the chemical\nreactions that we just", "start": 4894.13, "duration": 4.83}, {"text": "have to build a pathway\nfor, like gluconeogenesis.", "start": 4898.96, "duration": 3.48}, {"text": "Now these two things\nare often referred", "start": 4902.44, "duration": 2.04}, {"text": "to as the light and dark\nreactions of photosynthesis.", "start": 4904.48, "duration": 11.73}, {"text": "And that's because the\nfirst set of reactions", "start": 4916.21, "duration": 3.15}, {"text": "generating the membrane\npotential and making NADPH", "start": 4919.36, "duration": 3.84}, {"text": "requires solar energy inputs\nor requires light from the sun.", "start": 4923.2, "duration": 4.23}, {"text": "This fixing of CO2, which will\njust use electrons from NADPH", "start": 4927.43, "duration": 5.97}, {"text": "to reduce CO2, can occur--", "start": 4933.4, "duration": 2.868}, {"text": "of course, it can\noccur in the light.", "start": 4936.268, "duration": 1.542}, {"text": "But it doesn't need light.", "start": 4937.81, "duration": 1.21}, {"text": "So it can occur in\nthe light or the dark,", "start": 4939.02, "duration": 1.94}, {"text": "hence called the dark reactions.", "start": 4940.96, "duration": 2.59}, {"text": "And so these light reactions can\nreally be broken up into water", "start": 4943.55, "duration": 5.3}, {"text": "plus NADP+ goes to\nNADPH plus oxygen.", "start": 4948.85, "duration": 10.2}, {"text": "And the dark reactions are NADPH\nplus CO2 goes to carbohydrate", "start": 4959.05, "duration": 11.82}, {"text": "plus NADP+, which of\ncourse gives us our net--", "start": 4970.87, "duration": 7.98}, {"text": "water plus CO2 goes to\ncarbohydrate plus oxygen.", "start": 4978.85, "duration": 9.1}, {"text": "And in the next lecture,\nwhat we'll talk about is", "start": 4987.95, "duration": 2.91}, {"text": "we'll go through\nthe details of how", "start": 4990.86, "duration": 2.7}, {"text": "these light and\ndark reactions work.", "start": 4993.56, "duration": 3.96}, {"text": "But when we do so, bear\nin mind that we're really", "start": 4997.52, "duration": 2.79}, {"text": "going to follow all of\nthe concepts and rules", "start": 5000.31, "duration": 5.04}, {"text": "that we talked about for past\nthermodynamic considerations", "start": 5005.35, "duration": 4.77}, {"text": "of pathways as\nwell as what we've", "start": 5010.12, "duration": 2.49}, {"text": "been discussing about how\noxidative phosphorylation", "start": 5012.61, "duration": 3.21}, {"text": "works.", "start": 5015.82, "duration": 0.75}, {"text": "Thanks.", "start": 5016.57, "duration": 1.55}]