1 00:00:00,000 --> 00:00:01,912 [SQUEAKING] 2 00:00:01,912 --> 00:00:04,302 [RUSTLING] 3 00:00:04,302 --> 00:00:10,040 [CLICKING] 4 00:00:10,040 --> 00:00:14,480 PROFESSOR: Today we're going to discuss bioenergetics, continue 5 00:00:14,480 --> 00:00:18,020 that discussion and use that as a transition 6 00:00:18,020 --> 00:00:23,540 into also beginning to see how that applies to understanding 7 00:00:23,540 --> 00:00:28,620 glycolysis, the pathway that allows glucose breakdown. 8 00:00:28,620 --> 00:00:31,980 So just as a reminder of a couple of the points 9 00:00:31,980 --> 00:00:35,100 that we discussed last time, so last time 10 00:00:35,100 --> 00:00:37,780 we discussed what makes reactions favorable. 11 00:00:37,780 --> 00:00:41,430 And so remember, you could have any reaction, A to B-- 12 00:00:41,430 --> 00:00:43,020 A to B could be a single step. 13 00:00:43,020 --> 00:00:46,050 A to B could be an entire pathway, all steps 14 00:00:46,050 --> 00:00:49,260 in the pathway, that whether or not that reaction 15 00:00:49,260 --> 00:00:52,380 or pathway happens is determined by thermodynamics. 16 00:00:52,380 --> 00:00:54,130 It's not determined by enzymes. 17 00:00:54,130 --> 00:00:55,810 Enzymes are important, of course, 18 00:00:55,810 --> 00:00:58,560 to control the rate of reactions so they 19 00:00:58,560 --> 00:01:01,440 may allow things to happen that otherwise wouldn't happen. 20 00:01:01,440 --> 00:01:03,630 But whether the reaction happens or not 21 00:01:03,630 --> 00:01:06,310 is determined by free energy. 22 00:01:06,310 --> 00:01:08,370 And so free energy, delta G, remember 23 00:01:08,370 --> 00:01:11,770 we discussed is the following relationship. 24 00:01:11,770 --> 00:01:14,460 So it's related to this constant delta G0 25 00:01:14,460 --> 00:01:16,740 prime, which is related to the equilibrium 26 00:01:16,740 --> 00:01:20,970 constant for any pair of products and reactants 27 00:01:20,970 --> 00:01:25,020 as well as this formula rt times the log of the products 28 00:01:25,020 --> 00:01:26,980 over the reactants. 29 00:01:26,980 --> 00:01:30,780 And so remember this means that whether a reaction happens 30 00:01:30,780 --> 00:01:33,030 depends on the equilibrium constant, 31 00:01:33,030 --> 00:01:36,510 but it also depends on the actual conditions present. 32 00:01:36,510 --> 00:01:40,390 That is how much substrate and how much product is there. 33 00:01:40,390 --> 00:01:44,400 And so what this means is that biology can come up with ways 34 00:01:44,400 --> 00:01:48,150 by keeping the product concentrations low to do things 35 00:01:48,150 --> 00:01:51,510 that may move in the opposite direction of what you would 36 00:01:51,510 --> 00:01:54,210 predict from equilibrium. 37 00:01:54,210 --> 00:01:58,410 And also by coupling these less favorable reactions 38 00:01:58,410 --> 00:02:02,700 to more favorable reactions, you can also allow biology 39 00:02:02,700 --> 00:02:04,410 to do unfavorable stuff. 40 00:02:04,410 --> 00:02:07,260 And this is, of course, where the role of ATP comes in. 41 00:02:07,260 --> 00:02:11,180 And we discussed this at the end of last time as well. 42 00:02:11,180 --> 00:02:15,860 Of course, what's important then becomes the ratio of ATP 43 00:02:15,860 --> 00:02:17,300 to ADP. 44 00:02:17,300 --> 00:02:20,340 And to illustrate that, we use this example. 45 00:02:20,340 --> 00:02:25,160 We use the-- remember ATP hydrolysis has a delta G0 prime 46 00:02:25,160 --> 00:02:28,460 of minus 7.5 kcals per mole. 47 00:02:28,460 --> 00:02:30,048 That, of course, tells you this is 48 00:02:30,048 --> 00:02:31,340 about the equilibrium constant. 49 00:02:31,340 --> 00:02:34,010 That tells us the equilibrium lies to the right. 50 00:02:34,010 --> 00:02:37,400 We can couple it to this first reaction in glycolysis, 51 00:02:37,400 --> 00:02:40,880 which traps glucose in the cell by adding a phosphate group. 52 00:02:40,880 --> 00:02:45,200 Delta G0 prime for this is positive 3.3 kcals per mole. 53 00:02:45,200 --> 00:02:48,650 This positive number tells you that the equilibrium 54 00:02:48,650 --> 00:02:50,730 lies towards the left. 55 00:02:50,730 --> 00:02:53,300 But when we couple these two reactions together, 56 00:02:53,300 --> 00:02:55,250 we add these two numbers together, 57 00:02:55,250 --> 00:02:59,880 and now we get a delta G0 prime of minus 4.2 kcals per mole, 58 00:02:59,880 --> 00:03:01,580 which are the coupled reaction. 59 00:03:01,580 --> 00:03:04,220 The equilibrium lies now again to the right. 60 00:03:04,220 --> 00:03:07,430 And that's how we can use ATP hydrolysis in order 61 00:03:07,430 --> 00:03:10,280 to carry out this unfavorable process, trapping 62 00:03:10,280 --> 00:03:12,060 the glucose in the cell. 63 00:03:12,060 --> 00:03:15,140 Now how much glucose will be trapped? 64 00:03:15,140 --> 00:03:19,945 Well, of course, that will come from this reaction up here. 65 00:03:19,945 --> 00:03:21,320 And that's because whether or not 66 00:03:21,320 --> 00:03:22,970 a reaction occurs or not of course 67 00:03:22,970 --> 00:03:25,070 depends not on the equilibrium constant 68 00:03:25,070 --> 00:03:30,120 but on the actual conditions and the delta G of that reaction. 69 00:03:30,120 --> 00:03:33,060 And so we can just plug that in for this system. 70 00:03:33,060 --> 00:03:37,430 And so we see delta G0 prime minus 4.2 kcals per mole. 71 00:03:37,430 --> 00:03:39,230 That says equilibrium lies to the right. 72 00:03:39,230 --> 00:03:42,110 But how far really depends on the conditions. 73 00:03:42,110 --> 00:03:46,500 And that's defined by this ratio of products over reactants. 74 00:03:46,500 --> 00:03:49,070 And you can imagine that this term here, as long 75 00:03:49,070 --> 00:03:54,200 as it's less than 4.2, you will favor glucose trapping 76 00:03:54,200 --> 00:03:56,760 inside the cell, whereas, of course, 77 00:03:56,760 --> 00:03:59,210 if it's greater than 4.2, then you'd favor-- 78 00:03:59,210 --> 00:04:03,080 the opposite direction would be favorable. 79 00:04:03,080 --> 00:04:07,520 Now this is really critical because this really 80 00:04:07,520 --> 00:04:11,480 explains how it is that ATP actually 81 00:04:11,480 --> 00:04:17,760 works to help cells do various reactions. 82 00:04:17,760 --> 00:04:22,070 And so if an ATP-ADP ratio exists such 83 00:04:22,070 --> 00:04:24,680 that it can make delta G less than 0 84 00:04:24,680 --> 00:04:26,750 for the reaction that it's coupled to, 85 00:04:26,750 --> 00:04:30,320 that is how it provides the energy that then allows 86 00:04:30,320 --> 00:04:33,000 unfavorable reactions to occur. 87 00:04:33,000 --> 00:04:35,690 And so please do not make the common mistake 88 00:04:35,690 --> 00:04:38,855 that many, many biologists make when they state, 89 00:04:38,855 --> 00:04:41,030 oh, ATP equals energy. 90 00:04:41,030 --> 00:04:42,350 There's a lot of ATP. 91 00:04:42,350 --> 00:04:44,960 The cell must have a lot of energy. 92 00:04:44,960 --> 00:04:48,020 Remember it's the ratio of ATP to ADP 93 00:04:48,020 --> 00:04:49,680 that provides the energy. 94 00:04:49,680 --> 00:04:52,400 And so that means ATP can be sky high, 95 00:04:52,400 --> 00:04:57,170 but if ADP is equally high, there's no energy there. 96 00:04:57,170 --> 00:05:00,060 Consequently, ATP can be very low. 97 00:05:00,060 --> 00:05:03,260 But if ADP is extremely low, now you still 98 00:05:03,260 --> 00:05:05,790 have a high ATP to ADP ratio. 99 00:05:05,790 --> 00:05:08,570 And that is what provides the energy. 100 00:05:08,570 --> 00:05:11,570 And that's because this occurs regardless of concentration. 101 00:05:11,570 --> 00:05:15,590 It's because it's this ratio of ATP to ADP 102 00:05:15,590 --> 00:05:20,120 that ultimately says how much energy is there for the ATP 103 00:05:20,120 --> 00:05:22,680 to drive a reaction. 104 00:05:22,680 --> 00:05:26,540 In other words, delta G, or whatever the reaction 105 00:05:26,540 --> 00:05:29,630 is coupled to, is going to be proportional 106 00:05:29,630 --> 00:05:34,280 to the ratio of ADP to ATP. 107 00:05:34,280 --> 00:05:35,690 Great. 108 00:05:35,690 --> 00:05:38,270 Now how much ATP do you need then? 109 00:05:38,270 --> 00:05:40,895 What ratio do you need to drive a reaction? 110 00:05:40,895 --> 00:05:42,770 Well, it's hard to say that in absolute terms 111 00:05:42,770 --> 00:05:46,460 because it's going to be defined by how that ratio is coupled 112 00:05:46,460 --> 00:05:50,940 to the ratio of whatever other reactants and products. 113 00:05:50,940 --> 00:05:54,410 It also tells you, remember, as we talked about before, we 114 00:05:54,410 --> 00:05:56,690 can switch the directions of these reactions 115 00:05:56,690 --> 00:05:58,190 and we just flip the signs. 116 00:05:58,190 --> 00:06:01,280 The directions here are arbitrary. 117 00:06:01,280 --> 00:06:03,170 And so that means it also tells us 118 00:06:03,170 --> 00:06:06,290 how much energy we need to put in if we're going 119 00:06:06,290 --> 00:06:10,590 to charge up an ATP-ADP ratio. 120 00:06:10,590 --> 00:06:12,470 In other words, if we want to synthesize 121 00:06:12,470 --> 00:06:17,930 ATP, that is take ADP plus phosphate 122 00:06:17,930 --> 00:06:20,300 and make an ATP, well, what's this? 123 00:06:20,300 --> 00:06:22,490 What we just-- the exact opposite sign 124 00:06:22,490 --> 00:06:24,830 of that delta G0 prime is going to now equal 125 00:06:24,830 --> 00:06:31,230 plus 7.5 kcals per mole. 126 00:06:31,230 --> 00:06:35,940 And so that means that the equilibrium of this reaction 127 00:06:35,940 --> 00:06:40,470 is going to lie to the left just as that one lied to the right. 128 00:06:40,470 --> 00:06:43,720 And it's going to lie to the left by that much. 129 00:06:43,720 --> 00:06:45,990 And if we want to know how much energy it then 130 00:06:45,990 --> 00:06:49,410 takes to make ATP, well, obviously, it's 131 00:06:49,410 --> 00:06:51,390 not going to happen because equilibrium 132 00:06:51,390 --> 00:06:52,560 favors this direction. 133 00:06:52,560 --> 00:06:54,720 It's not spontaneous in that direction. 134 00:06:54,720 --> 00:06:56,970 But at various conditions, we can 135 00:06:56,970 --> 00:07:00,030 know by plugging in our formula delta G equals delta 136 00:07:00,030 --> 00:07:09,305 G0 prime plus 7.5 kcals per mole plus RT times the log of ATP. 137 00:07:17,520 --> 00:07:20,420 So if I have my ADP-- 138 00:07:20,420 --> 00:07:24,740 I'm sorry-- my ATP concentration sufficiently low relative 139 00:07:24,740 --> 00:07:27,410 to my ADP concentration, I can still 140 00:07:27,410 --> 00:07:29,720 make this reaction happen. 141 00:07:29,720 --> 00:07:32,360 Now that's not going to give you an ATP-ADP ratio that 142 00:07:32,360 --> 00:07:35,360 is actually consistent with being able to do anything 143 00:07:35,360 --> 00:07:36,930 else into the cell. 144 00:07:36,930 --> 00:07:43,970 And so but what it says is that if I am able to couple energy 145 00:07:43,970 --> 00:07:48,320 from nutrient metabolism to this reaction 146 00:07:48,320 --> 00:07:53,750 and overcome this positive 7.5 kcals per mole, 147 00:07:53,750 --> 00:08:00,425 that basically will allow me to now synthesize ATP and maintain 148 00:08:00,425 --> 00:08:06,170 an ATP-ADP ratio in the cell that allows cells to carry out 149 00:08:06,170 --> 00:08:08,030 other functions by the same rules 150 00:08:08,030 --> 00:08:10,920 that we talked about that would be unfavorable. 151 00:08:10,920 --> 00:08:16,160 Now there's lots of implications here for metabolism, 152 00:08:16,160 --> 00:08:20,270 because it says how much input you need to synthesize ATP. 153 00:08:20,270 --> 00:08:23,210 How much energy you need to synthesize ATP 154 00:08:23,210 --> 00:08:26,420 is going to depend on how charged this ratio is. 155 00:08:26,420 --> 00:08:29,810 And how useful that ratio is to catalyze other reactions 156 00:08:29,810 --> 00:08:35,539 is also going to depend on how charged that ratio is. 157 00:08:35,539 --> 00:08:39,590 And in essence, this is why we cannot store energy as ATP. 158 00:08:39,590 --> 00:08:42,409 This is why we didn't eat ATP for breakfast 159 00:08:42,409 --> 00:08:46,280 and instead ate cereal that has a bunch of glucose in it, 160 00:08:46,280 --> 00:08:50,420 because we can use that glucose to get ATP but the ATP itself 161 00:08:50,420 --> 00:08:53,660 is not something that we really can burn to get energy 162 00:08:53,660 --> 00:08:55,160 in a sustained way. 163 00:08:55,160 --> 00:09:02,180 In other words, the delta G of ATP synthesis, 164 00:09:02,180 --> 00:09:05,840 making ATP is going to be proportional 165 00:09:05,840 --> 00:09:12,770 to the log of the ratio of ATP over ADP for all the reasons 166 00:09:12,770 --> 00:09:14,420 I described. 167 00:09:14,420 --> 00:09:19,280 The delta G of using ATP, ATP hydrolysis, 168 00:09:19,280 --> 00:09:22,940 using ATP to drive reactions is also 169 00:09:22,940 --> 00:09:28,010 proportional to RT times the log, in this case, of the ADP 170 00:09:28,010 --> 00:09:30,950 to ATP ratio. 171 00:09:30,950 --> 00:09:34,850 And so because you need to consume this ratio to get 172 00:09:34,850 --> 00:09:40,460 energy, and you need to put in energy to create this ratio, 173 00:09:40,460 --> 00:09:45,110 you are constant-- and how much is an exponential property-- 174 00:09:45,110 --> 00:09:48,200 you are constantly having to generate 175 00:09:48,200 --> 00:09:50,990 ATP in a way that allows you to then 176 00:09:50,990 --> 00:09:54,050 have a ratio that can then be consumed 177 00:09:54,050 --> 00:09:56,450 to fuel other reactions. 178 00:09:56,450 --> 00:09:58,380 And that's what's shown here on the slide. 179 00:09:58,380 --> 00:10:02,090 So I just graphed here what the ATP-ADP ratio 180 00:10:02,090 --> 00:10:04,940 is relative to a theoretical delta 181 00:10:04,940 --> 00:10:10,040 G that's shown here as a linear scale, here on a log scale, 182 00:10:10,040 --> 00:10:13,530 that basically there's this logarithmic relationship 183 00:10:13,530 --> 00:10:17,660 and so you need an exponential increase in energy input 184 00:10:17,660 --> 00:10:21,860 to drive this ratio up higher in order to, quote unquote, 185 00:10:21,860 --> 00:10:25,190 "store" more energy that can be used for later. 186 00:10:25,190 --> 00:10:29,720 And so this system is not one that you can use as an energy 187 00:10:29,720 --> 00:10:32,630 storage system and ultimately explains 188 00:10:32,630 --> 00:10:35,480 why cells have to do constant metabolism, 189 00:10:35,480 --> 00:10:38,630 have to constantly do some sort of metabolism 190 00:10:38,630 --> 00:10:41,750 to keep this ATP-ADP ratio charged 191 00:10:41,750 --> 00:10:46,070 for it to be in a useful range to have an ATP-ADP ratio that 192 00:10:46,070 --> 00:10:48,830 can be coupled to drive otherwise 193 00:10:48,830 --> 00:10:52,640 unfavorable reactions in our cells. 194 00:10:52,640 --> 00:10:54,440 So to say this another way, our cells 195 00:10:54,440 --> 00:10:58,400 need to constantly catabolize nutrients, burn glucose, 196 00:10:58,400 --> 00:10:59,930 burn some other fuel. 197 00:10:59,930 --> 00:11:01,760 They have to do this because they 198 00:11:01,760 --> 00:11:05,000 have to keep that ratio charged in a range 199 00:11:05,000 --> 00:11:08,120 where that can then support other cell functions, 200 00:11:08,120 --> 00:11:15,160 allow them to fight entropy and maintain order in biology. 201 00:11:15,160 --> 00:11:18,610 We alluded last time if you stop making ATP, well, 202 00:11:18,610 --> 00:11:20,020 what's going to happen? 203 00:11:20,020 --> 00:11:22,030 Well, that ATP-ADP ratio the cell 204 00:11:22,030 --> 00:11:24,960 has is going to fuel whatever reactions it 205 00:11:24,960 --> 00:11:28,480 can do until suddenly that ratio falls below the point where 206 00:11:28,480 --> 00:11:31,930 it's useful to drive those unfavorable reactions. 207 00:11:31,930 --> 00:11:34,060 In fact, if you stop ATP production, 208 00:11:34,060 --> 00:11:37,840 you will consume that ATP-ADP ratio in seconds. 209 00:11:37,840 --> 00:11:40,300 And this is why if you poison ATP production, 210 00:11:40,300 --> 00:11:42,340 cells die very quickly. 211 00:11:42,340 --> 00:11:45,430 Remember last time we mentioned you have a heart attack, 212 00:11:45,430 --> 00:11:47,200 blood flow stops going to a tissue. 213 00:11:47,200 --> 00:11:50,380 No more nutrients and oxygen. Cells die quickly. 214 00:11:50,380 --> 00:11:52,750 Cyanide poisoning does the same thing. 215 00:11:52,750 --> 00:11:55,690 Cells die quickly if you stop their ability 216 00:11:55,690 --> 00:12:00,920 to maintain this ATP-ADP ratio in the right range. 217 00:12:00,920 --> 00:12:03,910 And so remember the concentration, 218 00:12:03,910 --> 00:12:07,030 the absolute concentration of ATP for these reasons 219 00:12:07,030 --> 00:12:09,980 is not a good indicator of cell energy. 220 00:12:09,980 --> 00:12:12,430 The correct indicator of cell energy 221 00:12:12,430 --> 00:12:17,670 is the ratio of ATP to ADP. 222 00:12:17,670 --> 00:12:24,960 This term is sometimes referred to as the energy charge. 223 00:12:24,960 --> 00:12:30,390 And so that can be the ATP to ADP ratio, 224 00:12:30,390 --> 00:12:37,530 or oftentimes more correctly is the ATP to AMP ratio. 225 00:12:37,530 --> 00:12:40,260 Why the ATP to AMP ratio? 226 00:12:40,260 --> 00:12:43,030 Well, that's because once you understand this, 227 00:12:43,030 --> 00:12:46,770 you can now understand that cells have a failsafe mechanism 228 00:12:46,770 --> 00:12:50,790 to protect themselves if this ratio of ATP to ADP 229 00:12:50,790 --> 00:12:52,770 becomes too low. 230 00:12:52,770 --> 00:12:54,150 What is that mechanism? 231 00:12:54,150 --> 00:12:56,850 Well, you can carry out this reaction. 232 00:12:56,850 --> 00:13:00,120 Take two ATP molecules and turn them 233 00:13:00,120 --> 00:13:05,880 into transfer a phosphate to make an ATP plus an AMP. 234 00:13:05,880 --> 00:13:07,680 Why is that a failsafe mechanism? 235 00:13:07,680 --> 00:13:11,640 Well, if they care about this, if the ATP-ADP ratio is 236 00:13:11,640 --> 00:13:14,580 what maintains your ability to drive 237 00:13:14,580 --> 00:13:17,340 these thermodynamically unfavorable reactions, 238 00:13:17,340 --> 00:13:21,090 if I sacrifice the denominator by removing an ATP 239 00:13:21,090 --> 00:13:24,750 and get an ATP out of it, I've now at least temporarily 240 00:13:24,750 --> 00:13:26,610 fixed that ratio. 241 00:13:26,610 --> 00:13:30,090 Now this is something that obviously cannot go on forever. 242 00:13:30,090 --> 00:13:32,490 But in the short term, it does allow 243 00:13:32,490 --> 00:13:35,020 cells to protect that ratio. 244 00:13:35,020 --> 00:13:39,870 And in fact, what cells actually defend is this ATP-AMP ratio. 245 00:13:39,870 --> 00:13:44,820 And it's very, very difficult to change the ATP-AMP ratio 246 00:13:44,820 --> 00:13:48,040 in a cell and actually have it live. 247 00:13:48,040 --> 00:13:50,730 So it's really this ATP-AMP ratio 248 00:13:50,730 --> 00:13:53,880 that is most formally related to what 249 00:13:53,880 --> 00:13:56,740 would be called energy charge. 250 00:13:56,740 --> 00:14:00,840 But this is really why this is important is 251 00:14:00,840 --> 00:14:03,880 for all the reasons that I just described. 252 00:14:03,880 --> 00:14:04,930 All right. 253 00:14:04,930 --> 00:14:07,840 So hopefully, it's clear to you now 254 00:14:07,840 --> 00:14:14,110 why cells have to keep ATP-ADP ratio in the right range, why 255 00:14:14,110 --> 00:14:16,570 this is useful for them to now carry out 256 00:14:16,570 --> 00:14:19,570 all of these unfavorable reactions-- fight entropy, 257 00:14:19,570 --> 00:14:22,590 stave off death. 258 00:14:22,590 --> 00:14:26,430 And they can even have a failsafe here and sacrifice ADP 259 00:14:26,430 --> 00:14:31,280 as a way to try to maintain that as a very last resort. 260 00:14:31,280 --> 00:14:34,390 It also says why cells have to always do catabolism, 261 00:14:34,390 --> 00:14:37,090 because you always need the energy input to keep 262 00:14:37,090 --> 00:14:39,970 that ratio in the right range. 263 00:14:39,970 --> 00:14:43,330 However, you might imagine that, in real life, 264 00:14:43,330 --> 00:14:46,180 the messiness of biology, that there's 265 00:14:46,180 --> 00:14:48,850 lots of situations where the demand for ATP 266 00:14:48,850 --> 00:14:51,310 will suddenly increase. 267 00:14:51,310 --> 00:14:53,950 Well, of course, maybe you can just metabolize more sugar, 268 00:14:53,950 --> 00:14:57,760 do more nutrient catabolism to try to keep that ratio high. 269 00:14:57,760 --> 00:14:59,480 But that takes time. 270 00:14:59,480 --> 00:15:03,610 And so you need ways for cells to quickly respond 271 00:15:03,610 --> 00:15:07,540 to then allow them to mobilize all of this extra thing to-- 272 00:15:07,540 --> 00:15:09,760 extra fuel to do that. 273 00:15:09,760 --> 00:15:13,000 For example, we're walking around our ancestors 274 00:15:13,000 --> 00:15:16,120 on the plains somewhere and a lion appears. 275 00:15:16,120 --> 00:15:20,020 We don't have time to mobilize a bunch of new fuel. 276 00:15:20,020 --> 00:15:22,670 We have to be able to run away really quickly 277 00:15:22,670 --> 00:15:24,610 or the lion's going to eat us. 278 00:15:24,610 --> 00:15:27,670 And so cells have systems to suddenly respond 279 00:15:27,670 --> 00:15:33,050 to I need a lot more ATP demand to run away by having ways 280 00:15:33,050 --> 00:15:37,040 that one can buffer this ATP-ADP ratio, 281 00:15:37,040 --> 00:15:40,940 protect it in the short term, and allow cells time 282 00:15:40,940 --> 00:15:45,360 to ramp up nutrient metabolism in order to keep this high. 283 00:15:45,360 --> 00:15:45,860 All right. 284 00:15:45,860 --> 00:15:48,800 Well, if we wanted to create such a buffer system, 285 00:15:48,800 --> 00:15:51,050 how would we actually do it? 286 00:15:51,050 --> 00:15:52,820 Well, obviously, we have to follow 287 00:15:52,820 --> 00:15:56,360 all the rules of thermodynamics that we discussed. 288 00:15:56,360 --> 00:15:58,970 And we have to do so in a way that 289 00:15:58,970 --> 00:16:01,550 actually illustrates how it is that 290 00:16:01,550 --> 00:16:04,620 very well how metabolism works. 291 00:16:04,620 --> 00:16:09,290 In other words, if suddenly the ATP-ADP ratio 292 00:16:09,290 --> 00:16:14,750 drops, if we have a sudden drop in ATP-ADP ratio 293 00:16:14,750 --> 00:16:16,400 because we have increased demand, 294 00:16:16,400 --> 00:16:19,070 needing to run away from a lion, how 295 00:16:19,070 --> 00:16:21,350 could we actually create a buffer system 296 00:16:21,350 --> 00:16:23,210 that protects this? 297 00:16:23,210 --> 00:16:28,010 Well, to do it, we would need to couple ATP-ADP 298 00:16:28,010 --> 00:16:30,920 to some other product reactant pair, 299 00:16:30,920 --> 00:16:37,850 let's call them x and y, such that the ratio of y to x 300 00:16:37,850 --> 00:16:44,180 is coupled to the ratio of ATP to ADP. 301 00:16:44,180 --> 00:16:46,670 And you want it coupled in such a way 302 00:16:46,670 --> 00:16:51,560 that if that ratio goes down, this ratio can now protect ATP, 303 00:16:51,560 --> 00:16:55,730 basically favor ATP to ADP synthesis. 304 00:16:55,730 --> 00:16:57,920 However, when nutrients are plentiful 305 00:16:57,920 --> 00:17:00,830 and this ratio is really high, it then in turn 306 00:17:00,830 --> 00:17:05,180 can charge up this ratio so that it can buffer it later 307 00:17:05,180 --> 00:17:09,210 when the ATP-ADP ratio starts to fall. 308 00:17:09,210 --> 00:17:12,300 Now the most famous example of this 309 00:17:12,300 --> 00:17:15,400 actually comes from muscle physiology. 310 00:17:15,400 --> 00:17:18,599 And it's best described in terms of muscles 311 00:17:18,599 --> 00:17:21,270 and how they quickly respond to increased demand, 312 00:17:21,270 --> 00:17:23,460 like that running away from a lion. 313 00:17:23,460 --> 00:17:26,670 However, it in fact applies to many, many cells, 314 00:17:26,670 --> 00:17:31,410 including most non-muscle cells in animals. 315 00:17:31,410 --> 00:17:32,790 All right. 316 00:17:32,790 --> 00:17:35,040 And I should say that it turns out 317 00:17:35,040 --> 00:17:38,520 that if you turn off ATP synthesis in a muscle, 318 00:17:38,520 --> 00:17:41,970 people have estimated that your ATP-ADP ratio will fall 319 00:17:41,970 --> 00:17:46,230 into a range where it is no longer useful to do anything 320 00:17:46,230 --> 00:17:50,820 within a matter of seconds, some claim even less than a second. 321 00:17:50,820 --> 00:17:54,580 And so this system ends up being very important. 322 00:17:54,580 --> 00:17:57,300 Now the system that muscle uses, and many other cells 323 00:17:57,300 --> 00:18:06,170 do as well, is something called the creatine/creatine phosphate 324 00:18:06,170 --> 00:18:07,550 system. 325 00:18:07,550 --> 00:18:10,790 Now if you guys are weightlifters or bodybuilders 326 00:18:10,790 --> 00:18:13,460 out there, you probably have heard of creatinine 327 00:18:13,460 --> 00:18:15,710 because it's a very popular supplement that 328 00:18:15,710 --> 00:18:19,160 is taken for weightlifting, something I obviously 329 00:18:19,160 --> 00:18:20,720 don't do a lot of. 330 00:18:20,720 --> 00:18:26,120 But that creatine/creatine phosphate is out there. 331 00:18:26,120 --> 00:18:30,410 I'll describe to you what it actually does for muscle cells. 332 00:18:30,410 --> 00:18:33,470 And you can decide for yourself if this is actually 333 00:18:33,470 --> 00:18:39,050 useful as a energy or weightlifting supplement. 334 00:18:39,050 --> 00:18:41,300 So what is creatine/creatine phosphate? 335 00:18:41,300 --> 00:18:42,600 What does it look like? 336 00:18:42,600 --> 00:18:45,410 Well, it's basically looks like this. 337 00:18:50,880 --> 00:18:54,090 By the way, I will use this abbreviation often 338 00:18:54,090 --> 00:18:56,310 throughout this course, just a shorthand 339 00:18:56,310 --> 00:18:58,360 to draw a lot of these structures. 340 00:18:58,360 --> 00:19:02,850 So this here would be a carboxylic acid group 341 00:19:02,850 --> 00:19:08,550 drawn like this or like that, drawn to the carboxylic acid 342 00:19:08,550 --> 00:19:12,510 group just so you understand my shorthand. 343 00:19:30,230 --> 00:19:30,920 OK. 344 00:19:30,920 --> 00:19:34,610 So this here is the molecule creatine. 345 00:19:34,610 --> 00:19:42,410 If I put a phosphate here, this now becomes creatine phosphate. 346 00:19:42,410 --> 00:19:45,350 Again, just to remind you, this P with a circle over it 347 00:19:45,350 --> 00:19:46,860 is a phosphate group. 348 00:19:46,860 --> 00:19:49,160 I'll draw this particular phosphate group 349 00:19:49,160 --> 00:19:51,770 because it's a nitrogen-phosphate bond, 350 00:19:51,770 --> 00:19:55,560 a phosphoramidate bond. 351 00:19:55,560 --> 00:19:59,160 This is actually a bond that is more labile than the PO bonds 352 00:19:59,160 --> 00:20:02,250 that we're used to seeing in the phosphodiesters like ATP, 353 00:20:02,250 --> 00:20:04,170 et cetera. 354 00:20:04,170 --> 00:20:04,800 All right. 355 00:20:04,800 --> 00:20:07,920 So that's creatine and creatine phosphate. 356 00:20:07,920 --> 00:20:18,910 And if we draw out the reaction, creatine phosphate 357 00:20:18,910 --> 00:20:26,680 goes to creatine plus inorganic phosphate, so hydrolysis 358 00:20:26,680 --> 00:20:28,330 of creatine phosphate. 359 00:20:28,330 --> 00:20:36,427 This has a delta G0 prime of minus 10 kcals per mole. 360 00:20:36,427 --> 00:20:37,260 What does that mean? 361 00:20:37,260 --> 00:20:38,983 It's negative. 362 00:20:38,983 --> 00:20:40,650 Tells us about the equilibrium constant. 363 00:20:40,650 --> 00:20:43,020 Equilibrium lies to the right. 364 00:20:43,020 --> 00:20:48,591 Remember ATP to ADP hydrolysis shown over there, 365 00:20:48,591 --> 00:20:51,090 that hydrolysis has a delta G0 prime 366 00:20:51,090 --> 00:20:53,760 of minus 7.5 kcals per mole. 367 00:20:53,760 --> 00:20:55,980 Equilibrium also lies to the right. 368 00:20:55,980 --> 00:20:57,570 This number is more negative. 369 00:20:57,570 --> 00:20:59,970 This equilibrium lies further to the right 370 00:20:59,970 --> 00:21:03,120 than ATP hydrolysis does. 371 00:21:03,120 --> 00:21:06,810 So now what happens if we couple this reaction 372 00:21:06,810 --> 00:21:09,040 to the ATP hydrolysis reaction? 373 00:21:09,040 --> 00:21:16,260 So now we can do ATP plus creatine goes 374 00:21:16,260 --> 00:21:23,510 to creatine phosphate plus ADP. 375 00:21:23,510 --> 00:21:26,640 So we've coupled those two reactions together. 376 00:21:26,640 --> 00:21:32,240 So delta G0 prime, ATP to ADP is minus 7.5. 377 00:21:32,240 --> 00:21:34,580 Creatine phosphate to creatine in 378 00:21:34,580 --> 00:21:37,730 that direction is negative 10. 379 00:21:37,730 --> 00:21:41,480 In this direction, it would be positive 10. 380 00:21:41,480 --> 00:21:43,640 And so as I've drawn the reaction, 381 00:21:43,640 --> 00:21:49,700 this delta G0 prime will be plus 2.5 kcals per mole. 382 00:21:49,700 --> 00:21:56,590 10 minus 7.5 plus 2.5, which tells us then 383 00:21:56,590 --> 00:22:01,960 that this equilibrium now lies to the left. 384 00:22:01,960 --> 00:22:06,880 However, which direction this reaction actually goes 385 00:22:06,880 --> 00:22:10,120 is not determined only by the equilibrium. 386 00:22:10,120 --> 00:22:14,210 It's really determined by delta G. So we can calculate that. 387 00:22:14,210 --> 00:22:20,800 So delta G equals delta G0 prime plus RT 388 00:22:20,800 --> 00:22:37,340 log of, as we've drawn it, creatine phosphate 389 00:22:37,340 --> 00:22:41,690 over creatine and ADP over ATP. 390 00:22:41,690 --> 00:22:45,920 So you can now imagine that this term here 391 00:22:45,920 --> 00:22:47,460 is the sum of those two. 392 00:22:47,460 --> 00:22:50,450 So it's plus 2.5. 393 00:22:50,450 --> 00:22:59,370 And so if this term is less than 2.5, what does that mean? 394 00:22:59,370 --> 00:23:00,680 Well, if it's-- 395 00:23:00,680 --> 00:23:01,310 I'm sorry. 396 00:23:01,310 --> 00:23:06,290 Less than negative 2.5, then delta G will be negative 397 00:23:06,290 --> 00:23:09,890 and you will favor creatine phosphate production. 398 00:23:09,890 --> 00:23:14,420 If this term is greater than negative 2.5, 399 00:23:14,420 --> 00:23:17,030 then delta G will be positive and you 400 00:23:17,030 --> 00:23:20,360 will favor ATP production. 401 00:23:20,360 --> 00:23:22,020 Why is that important? 402 00:23:22,020 --> 00:23:24,950 Well, if you think about the conditions, 403 00:23:24,950 --> 00:23:28,190 how you could make this term less than 2.5 404 00:23:28,190 --> 00:23:32,600 or less than negative 2.5 or greater than negative 2.5, 405 00:23:32,600 --> 00:23:34,130 basically, what's going to happen 406 00:23:34,130 --> 00:23:42,620 is that if the ATP-ADP ratio is high, 407 00:23:42,620 --> 00:23:45,710 lots of energy around, no problems charging up, 408 00:23:45,710 --> 00:23:49,520 lots of things to use, charge up this ATP/ADP to a very 409 00:23:49,520 --> 00:23:53,480 high ratio, well, now you will favor this direction, 410 00:23:53,480 --> 00:23:55,880 creatine phosphate synthesis. 411 00:23:55,880 --> 00:24:03,380 However, if ATP/ADP begins to fall and is lower, 412 00:24:03,380 --> 00:24:07,340 well, now this term is going to flip 413 00:24:07,340 --> 00:24:10,970 and you'll now favor ATP production. 414 00:24:10,970 --> 00:24:15,380 And so basically, by charging up this creatine/creatine 415 00:24:15,380 --> 00:24:18,410 phosphate ratio, it now creates a situation 416 00:24:18,410 --> 00:24:22,910 where it can buffer that ATP/ADP ratio so that when times are 417 00:24:22,910 --> 00:24:24,680 good, you charge up the buffer. 418 00:24:24,680 --> 00:24:27,560 When times are bad, you then consume the buffer 419 00:24:27,560 --> 00:24:31,520 in a way that allows you to protect your ATP/ADP 420 00:24:31,520 --> 00:24:33,330 ratio for a short time. 421 00:24:33,330 --> 00:24:35,210 And this is illustrated very nicely here 422 00:24:35,210 --> 00:24:38,330 in this slide that basically shows what 423 00:24:38,330 --> 00:24:40,020 happens in muscle physiology. 424 00:24:40,020 --> 00:24:42,500 And so this is just a theoretical curve 425 00:24:42,500 --> 00:24:45,830 that if you suddenly need to contract your muscle 426 00:24:45,830 --> 00:24:50,090 and you stop ATP production, well, ATP levels will fall. 427 00:24:50,090 --> 00:24:54,350 That ATP/ADP ratio more correctly will fall rapidly 428 00:24:54,350 --> 00:24:55,820 within the cell. 429 00:24:55,820 --> 00:24:59,030 Creatine phosphate will then now kick in 430 00:24:59,030 --> 00:25:03,620 to protect that ATP/ADP ratio as you can ramp up 431 00:25:03,620 --> 00:25:07,250 either anaerobic or aerobic metabolism to now buffer 432 00:25:07,250 --> 00:25:13,450 that ATP/ADP ratio and keep that muscle functioning. 433 00:25:13,450 --> 00:25:17,680 Now I want to make one point because oftentimes biochemistry 434 00:25:17,680 --> 00:25:21,280 textbooks will refer to things like ATP 435 00:25:21,280 --> 00:25:24,140 or creatine phosphate as, quote unquote, 436 00:25:24,140 --> 00:25:26,860 "high energy compounds." 437 00:25:26,860 --> 00:25:28,810 And of course, I guess they are high energy 438 00:25:28,810 --> 00:25:31,780 because they have these labile phosphate-nitrogen 439 00:25:31,780 --> 00:25:35,690 or phosphate-oxygen bonds. 440 00:25:35,690 --> 00:25:38,320 And because they're labile, hydrolysis is favorable. 441 00:25:38,320 --> 00:25:41,560 And to a certain extent, it's that hydrolysis 442 00:25:41,560 --> 00:25:44,710 that is providing energy. 443 00:25:44,710 --> 00:25:46,810 But remember it's not the metabolite 444 00:25:46,810 --> 00:25:50,650 or the bond in isolation that's really providing the energy. 445 00:25:50,650 --> 00:25:56,380 It's these ratios of ATP to ADP, creatine phosphate to creatine, 446 00:25:56,380 --> 00:25:59,200 that allow you to couple, for all the reasons 447 00:25:59,200 --> 00:26:01,750 we've spent now a lecture and a half discussing, 448 00:26:01,750 --> 00:26:08,380 two other reactions that really provides biological energy. 449 00:26:08,380 --> 00:26:11,120 All right. 450 00:26:11,120 --> 00:26:13,490 Now we're ready to discuss how it 451 00:26:13,490 --> 00:26:19,130 is that we can use glucose oxidation, nutrient catabolism, 452 00:26:19,130 --> 00:26:24,890 to keep ATP/ADP high, that is in a useful range, where it can 453 00:26:24,890 --> 00:26:27,890 allow cells to do otherwise thermodynamically 454 00:26:27,890 --> 00:26:29,570 unfavorable things. 455 00:26:29,570 --> 00:26:32,550 So how could we make this happen? 456 00:26:32,550 --> 00:26:35,960 Well, just like this example with creatine and creatine 457 00:26:35,960 --> 00:26:39,350 phosphate, if we want to use nutrient catabolism 458 00:26:39,350 --> 00:26:43,700 to do the same thing, we need to couple reactions 459 00:26:43,700 --> 00:26:46,940 of glucose oxidation, nutrient catabolism, that 460 00:26:46,940 --> 00:26:51,500 will allow us to synthesize ATP, ADP to ATP, 461 00:26:51,500 --> 00:26:53,810 and have that synthesis be favorable 462 00:26:53,810 --> 00:26:59,150 despite the high ATP/ADP ratio in cells. 463 00:26:59,150 --> 00:27:00,660 So let's think about it. 464 00:27:00,660 --> 00:27:01,730 So what is this? 465 00:27:01,730 --> 00:27:02,900 Nutrient catabolism. 466 00:27:02,900 --> 00:27:04,520 What did we talk about last time? 467 00:27:04,520 --> 00:27:08,480 Oxidizing glucose to carbon and CO2. 468 00:27:08,480 --> 00:27:11,580 So here's our reaction for that. 469 00:27:11,580 --> 00:27:19,880 So here's carbohydrate, glucose CH2O6 plus six O2 470 00:27:19,880 --> 00:27:25,850 goes to six CO2 plus six H2O. 471 00:27:25,850 --> 00:27:33,170 That's the chemical formula for burning wood. 472 00:27:33,170 --> 00:27:41,570 So delta G0 prime for this is minus 686 kcals per mole. 473 00:27:44,720 --> 00:27:46,460 Quite a negative number. 474 00:27:46,460 --> 00:27:52,850 Equilibrium greatly favors the completely burned state, 475 00:27:52,850 --> 00:27:56,880 oxidized state, of that carbohydrate. 476 00:27:56,880 --> 00:27:59,360 And so you can imagine that this equilibrium is 477 00:27:59,360 --> 00:28:04,160 so favorable to the right, if we couple this reaction to ATP 478 00:28:04,160 --> 00:28:08,240 synthesis, you're clearly going to have plenty of energy there 479 00:28:08,240 --> 00:28:10,580 in order to maintain that ATP/ADP 480 00:28:10,580 --> 00:28:15,350 ratio in the right range to be compatible with cells 481 00:28:15,350 --> 00:28:17,670 using it to do other things. 482 00:28:17,670 --> 00:28:18,170 All right. 483 00:28:18,170 --> 00:28:21,600 So how do we actually do that? 484 00:28:21,600 --> 00:28:23,720 Well, if we do it, we have to follow 485 00:28:23,720 --> 00:28:27,050 the same rules of thermodynamics and do the same things 486 00:28:27,050 --> 00:28:28,130 that we did before. 487 00:28:28,130 --> 00:28:34,160 Basically, we have to do this reaction in a way 488 00:28:34,160 --> 00:28:37,820 that we can draw out a similar type of equation 489 00:28:37,820 --> 00:28:41,360 as we did for creatine and creatine phosphate. 490 00:28:41,360 --> 00:28:45,650 And at the highest level, that is how nutrient catabolism 491 00:28:45,650 --> 00:28:49,620 will allow us to keep ATP/ADP ratio high 492 00:28:49,620 --> 00:28:52,910 even as ATP hydrolysis is constantly 493 00:28:52,910 --> 00:28:56,540 fueling all these other unfavorable processes 494 00:28:56,540 --> 00:28:58,810 in the cell. 495 00:28:58,810 --> 00:29:03,510 Now if we did this all in one step, our burning wood example, 496 00:29:03,510 --> 00:29:06,320 lots of heat is generated. 497 00:29:06,320 --> 00:29:07,760 That's too much energy. 498 00:29:07,760 --> 00:29:11,210 Not so good for biology. 499 00:29:11,210 --> 00:29:15,320 But rather what biology does, as we alluded to last time, 500 00:29:15,320 --> 00:29:17,780 is that because what we talked about in the beginning, 501 00:29:17,780 --> 00:29:20,150 that all of the things that we discussed 502 00:29:20,150 --> 00:29:22,610 are true for individual reactions 503 00:29:22,610 --> 00:29:28,370 or many, many reactions, basically, if we turn A into B 504 00:29:28,370 --> 00:29:31,400 and we do it in one step, like burning wood, 505 00:29:31,400 --> 00:29:37,400 or we do it in 500 steps, the thermodynamic consequences 506 00:29:37,400 --> 00:29:39,570 are exactly the same. 507 00:29:39,570 --> 00:29:45,530 And so what we need to do is do stepwise catabolism of glucose 508 00:29:45,530 --> 00:29:48,890 and take advantage of the fact that that delta G change is 509 00:29:48,890 --> 00:29:52,820 the same whether it's one step or many steps 510 00:29:52,820 --> 00:29:57,830 and in that stepwise fashion build in reactions where 511 00:29:57,830 --> 00:30:03,500 we create intermediate chemistries that allow us to do 512 00:30:03,500 --> 00:30:06,740 things like we did with creatine and creatine phosphate 513 00:30:06,740 --> 00:30:12,110 such that we can favor ATP synthesis when ATP/ADP ratio is 514 00:30:12,110 --> 00:30:14,130 in the physiological range. 515 00:30:14,130 --> 00:30:16,010 And in essence, this is the magic 516 00:30:16,010 --> 00:30:22,800 of how biology does this and basically couples 517 00:30:22,800 --> 00:30:26,770 nutrient catabolism in order to provide energy. 518 00:30:26,770 --> 00:30:30,330 And so the pathway that we're going to discuss today 519 00:30:30,330 --> 00:30:31,860 and in the next lecture is something 520 00:30:31,860 --> 00:30:41,130 called glycolysis, which simply put is glucose lysis. 521 00:30:41,130 --> 00:30:45,060 It's the stepwise chemical oxidation 522 00:30:45,060 --> 00:30:47,640 of glucose, which we know from our burning wood 523 00:30:47,640 --> 00:30:49,500 example is favorable. 524 00:30:49,500 --> 00:30:54,150 And we're going to use this pathway that basically will 525 00:30:54,150 --> 00:30:58,350 be a pathway to allow the stepwise lysis of glucose, 526 00:30:58,350 --> 00:31:03,180 a favorable reaction, to individual steps that set it up 527 00:31:03,180 --> 00:31:06,360 in a way such that ADP to ATP synthesis 528 00:31:06,360 --> 00:31:12,780 is favored despite a physiological ATP/ADP ratio. 529 00:31:12,780 --> 00:31:15,720 Now I want to point out that this really illustrates, 530 00:31:15,720 --> 00:31:18,360 back to that high energy compound thing, 531 00:31:18,360 --> 00:31:21,220 that ATP is not the only energy currency in the cell. 532 00:31:21,220 --> 00:31:26,370 In fact, glucose is much more energy for a cell than ATP. 533 00:31:26,370 --> 00:31:29,910 You get much more energy released from burning wood 534 00:31:29,910 --> 00:31:32,670 than you get from hydrolyzing ATP. 535 00:31:32,670 --> 00:31:35,040 And in essence, this is why we use 536 00:31:35,040 --> 00:31:38,400 glucose-- why nature has used glucose, 537 00:31:38,400 --> 00:31:41,940 and other molecules like it, as an energy storage 538 00:31:41,940 --> 00:31:44,880 device, because here is a relatively stable molecule, 539 00:31:44,880 --> 00:31:47,490 can sit around for a long time, and you 540 00:31:47,490 --> 00:31:52,670 can burn it when you need it to keep your ATP-ADP ratio high. 541 00:31:52,670 --> 00:31:54,080 All right. 542 00:31:54,080 --> 00:31:57,260 So, at the level of reactions and pathways 543 00:31:57,260 --> 00:32:01,520 now, how can we use glucose oxidation and couple 544 00:32:01,520 --> 00:32:03,140 it to drive ATP synthesis? 545 00:32:03,140 --> 00:32:05,540 Well, hopefully it's very clear that we 546 00:32:05,540 --> 00:32:07,400 have to basically set up a situation 547 00:32:07,400 --> 00:32:09,230 like this creatine-creatine-phosphate 548 00:32:09,230 --> 00:32:12,540 system that we already discussed. 549 00:32:12,540 --> 00:32:15,200 And so I want to start by discussing, 550 00:32:15,200 --> 00:32:19,220 what are the reactions in glycolysis that ultimately 551 00:32:19,220 --> 00:32:27,620 behave like this and allow this favorable ADP-to-ATP synthesis? 552 00:32:27,620 --> 00:32:30,350 And then we will go ahead and consider 553 00:32:30,350 --> 00:32:33,380 how we can make those reactions work 554 00:32:33,380 --> 00:32:36,560 in the context of an entire pathway that 555 00:32:36,560 --> 00:32:40,550 allows glucose oxidation. 556 00:32:40,550 --> 00:32:42,680 All right. 557 00:32:42,680 --> 00:32:49,050 Now, like creatine, phosphate, and creatine, 558 00:32:49,050 --> 00:32:52,080 both of the steps in glycolysis that 559 00:32:52,080 --> 00:32:56,190 favor ATP synthesis involve intermediates 560 00:32:56,190 --> 00:33:01,860 where you have phosphate on some molecule, 561 00:33:01,860 --> 00:33:09,210 plus ADP goes to ATP plus the phosphate 562 00:33:09,210 --> 00:33:11,170 coming off that molecule. 563 00:33:11,170 --> 00:33:14,040 Now, if we go to our creatine-creatine-phosphate 564 00:33:14,040 --> 00:33:17,370 system, obviously this equilibrium 565 00:33:17,370 --> 00:33:20,340 needs to lie to the right. 566 00:33:20,340 --> 00:33:25,650 And so the first one of these is as follows. 567 00:33:52,020 --> 00:33:56,980 It involves this molecule, phosphoenolpyruvate, also 568 00:33:56,980 --> 00:33:59,403 referred to as PEP. 569 00:33:59,403 --> 00:34:00,820 You will see throughout the course 570 00:34:00,820 --> 00:34:04,360 that we love to give these little acronyms 571 00:34:04,360 --> 00:34:07,450 to our metabolites because it's hard to constantly 572 00:34:07,450 --> 00:34:09,699 say and write out phosphoenolpyruvate. 573 00:34:09,699 --> 00:34:12,190 Much easier to say PEP. 574 00:34:12,190 --> 00:34:19,929 So phosphoenolpyruvate plus ADP goes to ATP. 575 00:34:19,929 --> 00:34:22,840 Plus, if I take the phosphate off of there, 576 00:34:22,840 --> 00:34:24,219 I get this molecule. 577 00:34:30,340 --> 00:34:33,875 This molecule is enolpyruvate. 578 00:34:38,230 --> 00:34:43,525 Enolpyruvate can be rearranged as follows. 579 00:35:04,200 --> 00:35:08,370 To make this molecule a ketone pyruvate. 580 00:35:08,370 --> 00:35:11,040 You'll note-- hopefully remember from your organic chemistry 581 00:35:11,040 --> 00:35:13,920 classes that ketones like pyruvate 582 00:35:13,920 --> 00:35:15,300 can exist in two forms. 583 00:35:15,300 --> 00:35:18,690 They can exist in the ketone form or the enol form, 584 00:35:18,690 --> 00:35:21,990 rearranging via the chemistry that I've shown. 585 00:35:21,990 --> 00:35:33,770 The keto form is greatly favored over the enol form. 586 00:35:33,770 --> 00:35:38,690 However, by having a phosphate trap pyruvate the enol form-- 587 00:35:38,690 --> 00:35:42,140 phosphoenolpyruvate, when you remove the phosphate 588 00:35:42,140 --> 00:35:45,290 and it's wanting to exist in the keto form, 589 00:35:45,290 --> 00:35:49,010 greatly enhances the energetics of this-- 590 00:35:49,010 --> 00:35:51,260 basically makes the reaction, the equilibrium 591 00:35:51,260 --> 00:35:54,260 want to lie very far to the right. 592 00:35:54,260 --> 00:35:56,750 And by the way of chemical tricks like this 593 00:35:56,750 --> 00:36:02,330 and others like it, you will see used over and over in biology. 594 00:36:02,330 --> 00:36:04,490 In fact, this is illustrated, if we 595 00:36:04,490 --> 00:36:07,730 asked what's delta G0 prime for this reaction, 596 00:36:07,730 --> 00:36:14,560 it's minus 15 kcals per mole. 597 00:36:14,560 --> 00:36:18,100 That tells us that the equilibrium of this reaction 598 00:36:18,100 --> 00:36:19,120 lies to the right. 599 00:36:19,120 --> 00:36:23,520 In fact, it lies far to the right, and in fact, this is-- 600 00:36:23,520 --> 00:36:29,360 you may remember ATP hydrolysis is negative 7.5 kcals per mole. 601 00:36:29,360 --> 00:36:35,380 So lies twice as far to the right as ATP hydrolysis does. 602 00:36:35,380 --> 00:36:41,830 And in fact, this minus 15 kcals per mole is the most favorable, 603 00:36:41,830 --> 00:36:44,950 at least in terms of individual reactions 604 00:36:44,950 --> 00:36:48,940 that at least I know of in metabolism. 605 00:36:48,940 --> 00:36:49,990 All right. 606 00:36:49,990 --> 00:37:02,930 Well, if this equilibrium for this is PEP to pyruvate, 607 00:37:02,930 --> 00:37:06,095 this here is delta G0 prime for ATP-ADP. 608 00:37:10,130 --> 00:37:12,200 So if we want to know what's delta G0 609 00:37:12,200 --> 00:37:17,130 prime for the entire reaction, well, if PEP to pyruvate 610 00:37:17,130 --> 00:37:21,990 is minus 15, ATP to ADP is minus 7.5. 611 00:37:21,990 --> 00:37:24,100 Well here, we're going in the opposite direction, 612 00:37:24,100 --> 00:37:25,890 so it'd be plus 7.5. 613 00:37:25,890 --> 00:37:31,230 So it's minus 15 plus 7.5, means that for the entire reaction, 614 00:37:31,230 --> 00:37:36,660 this is minus 7.5 kcals per mole. 615 00:37:36,660 --> 00:37:41,430 Means that this is favorable, equilibrium lies to the right. 616 00:37:41,430 --> 00:37:42,420 If we drew out-- 617 00:37:42,420 --> 00:37:45,340 I'm not going to do it again because I've done it a lot, 618 00:37:45,340 --> 00:37:47,400 but if we redrew out this equation, 619 00:37:47,400 --> 00:37:50,580 replacing pyruvate and PEP in the correct places, 620 00:37:50,580 --> 00:37:53,040 there for creatine, phosphate, and creatine, 621 00:37:53,040 --> 00:37:56,040 you would see that there's lots of conditions within cells 622 00:37:56,040 --> 00:37:59,250 that will favor ATP synthesis even 623 00:37:59,250 --> 00:38:03,820 when ATP-ADP ratio is high. 624 00:38:03,820 --> 00:38:04,320 All right. 625 00:38:04,320 --> 00:38:11,505 This reaction is catalyzed by an enzyme called pyruvate kinase. 626 00:38:17,570 --> 00:38:23,570 And pyruvate kinase is a classic example of a, quote-unquote, 627 00:38:23,570 --> 00:38:26,550 "irreversible reaction." 628 00:38:26,550 --> 00:38:29,600 However, I want to point out that the enzyme pyruvate 629 00:38:29,600 --> 00:38:33,830 kinase is actually named for the reverse reaction that's 630 00:38:33,830 --> 00:38:36,210 supposedly irreversible. 631 00:38:36,210 --> 00:38:37,170 Pyruvate kinase. 632 00:38:37,170 --> 00:38:39,680 If you take pyruvate and you act on the kinase 633 00:38:39,680 --> 00:38:41,530 as you learn from Professor Yaffe, 634 00:38:41,530 --> 00:38:42,780 that phosphorylates something. 635 00:38:42,780 --> 00:38:44,238 You phosphorylate pyruvate, you get 636 00:38:44,238 --> 00:38:47,220 phosphoenolpyruvate pyruvate kinase. 637 00:38:47,220 --> 00:38:54,590 And so remember that absolutely no reaction is reversible. 638 00:38:54,590 --> 00:38:57,440 It's only reversed-- what they mean by irreversible when they 639 00:38:57,440 --> 00:39:00,980 say pyruvate kinase step in glycolysis is irreversible, 640 00:39:00,980 --> 00:39:04,220 is that it is effectively irreversible 641 00:39:04,220 --> 00:39:07,190 under the conditions that are compatible with life 642 00:39:07,190 --> 00:39:09,110 that exist in cells. 643 00:39:09,110 --> 00:39:14,600 Of course, if you have very low ADP and very high ATP, 644 00:39:14,600 --> 00:39:19,400 you can come up with a way to net synthesize PEP. 645 00:39:19,400 --> 00:39:23,180 You just can't drive the reverse reaction 646 00:39:23,180 --> 00:39:27,080 under the ATP-ADP and the PEP pyruvate ratios that 647 00:39:27,080 --> 00:39:30,160 physiologically exist in cells. 648 00:39:30,160 --> 00:39:33,190 However, this is set up in a way such 649 00:39:33,190 --> 00:39:38,050 that you can favor ADP-to-ATP synthesis by converting 650 00:39:38,050 --> 00:39:41,050 PEP to pyruvate in a pathway, as we 651 00:39:41,050 --> 00:39:44,440 will see happens in glycolysis. 652 00:39:44,440 --> 00:39:45,640 All right. 653 00:39:45,640 --> 00:39:50,780 Now, the second reaction that I want to-- 654 00:39:50,780 --> 00:39:56,360 that allows ATP synthesis in glycolysis 655 00:39:56,360 --> 00:40:10,050 is catalyzed by an enzyme called phosphoglycerate kinase. 656 00:40:10,050 --> 00:40:13,630 And this carries out the following reaction. 657 00:40:27,660 --> 00:40:28,160 OK. 658 00:40:28,160 --> 00:40:41,090 So this molecule is 1,3-Bisphosphoglycerate, 659 00:40:41,090 --> 00:40:42,830 abbreviated 1,3-BPG. 660 00:41:08,120 --> 00:41:13,120 And basically the phosphate is transferred from here 661 00:41:13,120 --> 00:41:24,050 to ADP, which gives you this molecule, 3-phosphoglycerate 662 00:41:24,050 --> 00:41:24,710 or 3-PG. 663 00:41:28,750 --> 00:41:32,830 So this reaction, the delta G0 prime 664 00:41:32,830 --> 00:41:36,790 for the entire coupled reaction, both steps of the reaction, 665 00:41:36,790 --> 00:41:42,222 is minus 4.5 kcals per mole. 666 00:41:42,222 --> 00:41:43,930 Tells you about the equilibrium constant. 667 00:41:43,930 --> 00:41:47,650 Equilibrium lies to the right, doesn't lie as far to the right 668 00:41:47,650 --> 00:41:52,660 as the PEP plus ADP goes to ATP plus pyruvate reaction, 669 00:41:52,660 --> 00:41:55,660 but nonetheless, is one where there's 670 00:41:55,660 --> 00:42:00,640 lots of conditions that are favorable in cells to maintain 671 00:42:00,640 --> 00:42:04,630 a high ATP-ADP ratio, although we will see later 672 00:42:04,630 --> 00:42:08,393 that this reaction actually runs quite close to equilibrium 673 00:42:08,393 --> 00:42:10,060 in cells, so there's actually conditions 674 00:42:10,060 --> 00:42:12,250 where it can go in the opposite direction as well, 675 00:42:12,250 --> 00:42:15,290 and we'll get to that later in the course. 676 00:42:15,290 --> 00:42:17,710 I want to point out one thing about this, one thing that 677 00:42:17,710 --> 00:42:20,290 makes this reaction favorable, as you notice here 678 00:42:20,290 --> 00:42:23,980 that this is a phosphate on an acid group, 679 00:42:23,980 --> 00:42:26,290 a so-called acid anhydride. 680 00:42:26,290 --> 00:42:29,180 And this is a pretty good phosphate donor. 681 00:42:29,180 --> 00:42:31,840 And so you want to lose that phosphate, which 682 00:42:31,840 --> 00:42:35,200 is one of the reasons why this reaction is 683 00:42:35,200 --> 00:42:42,160 favorable for ATP synthesis even at high ATP-ADP ratios. 684 00:42:42,160 --> 00:42:44,020 All right. 685 00:42:44,020 --> 00:42:46,930 So these are the two reactions in glycolysis 686 00:42:46,930 --> 00:42:50,560 that can favor ATP synthesis at a high ATP-ADP ratio 687 00:42:50,560 --> 00:42:53,210 just like creatine and creatine phosphate. 688 00:42:53,210 --> 00:42:58,330 And so hopefully now it's become apparent to you that if during 689 00:42:58,330 --> 00:43:02,230 our pathway of glucose catabolism we can build 690 00:43:02,230 --> 00:43:07,030 a pathway that couples what we already know is favorable, 691 00:43:07,030 --> 00:43:10,640 glucose oxidation, to generate these intermediates, 692 00:43:10,640 --> 00:43:15,970 PEP and 1,3-Bisphosphoglycerate, lacerate we can then build 693 00:43:15,970 --> 00:43:20,560 a pathway where those reactions can make synthesis of ATP 694 00:43:20,560 --> 00:43:25,640 favorable even though there's a high ATP-ADP ratio in cells, 695 00:43:25,640 --> 00:43:29,560 and in fact, maintain that high ATP-ADP ratio in cells. 696 00:43:29,560 --> 00:43:32,750 And in essence, this is the logic or the goal, 697 00:43:32,750 --> 00:43:36,490 if you will, of glycolysis and why 698 00:43:36,490 --> 00:43:40,975 it's important to provide energy to cells. 699 00:43:40,975 --> 00:43:41,475 OK. 700 00:44:14,170 --> 00:44:14,800 All right. 701 00:44:14,800 --> 00:44:22,100 Now, if we're going to make a pathway where glucose oxidation 702 00:44:22,100 --> 00:44:27,310 is coupled to making PEP and 1,3-Bisphosphoglycerate, 703 00:44:27,310 --> 00:44:32,730 it's obvious we need to add phosphate to the system. 704 00:44:32,730 --> 00:44:37,020 There's no phosphate molecule on glucose. 705 00:44:37,020 --> 00:44:39,510 Now already mentioned earlier-- 706 00:44:39,510 --> 00:44:41,520 and I just erased it-- 707 00:44:41,520 --> 00:44:46,770 that to trap glucose in the cell, the first step 708 00:44:46,770 --> 00:44:50,220 in glycolysis, you add phosphate. 709 00:44:50,220 --> 00:44:53,280 But that phosphate donor is ATP. 710 00:44:53,280 --> 00:44:57,330 And so ATP being the phosphate donor doesn't help us here. 711 00:44:57,330 --> 00:44:59,970 If we're going to use phosphate transfer here, 712 00:44:59,970 --> 00:45:03,540 we need to have phosphate added into the system 713 00:45:03,540 --> 00:45:04,830 if this is going to work. 714 00:45:04,830 --> 00:45:08,280 We can't have ATP as our phosphate donor. 715 00:45:08,280 --> 00:45:12,780 You also saw lots of reactions from Professor Yaffe 716 00:45:12,780 --> 00:45:15,990 that involved phosphate transfer reactions. 717 00:45:15,990 --> 00:45:21,820 But again, ATP-- or GTP is the phosphate donor. 718 00:45:21,820 --> 00:45:27,030 And so for this system to work, we need a way to get inorganic 719 00:45:27,030 --> 00:45:33,780 phosphate onto a carbohydrate or we can't make things like PEP 720 00:45:33,780 --> 00:45:38,970 or 1,3-Bisphosphoglycerate that will allow ATP synthesis. 721 00:45:38,970 --> 00:45:43,860 Now we already saw earlier that additional phosphate to glucose 722 00:45:43,860 --> 00:45:45,120 is not favored. 723 00:45:45,120 --> 00:45:49,170 Remember, delta G0 prime of phosphorylating glucose 724 00:45:49,170 --> 00:45:53,540 was plus 3.3 kcals per mole. 725 00:45:53,540 --> 00:45:55,480 And it turns out that says equilibrium 726 00:45:55,480 --> 00:45:58,780 lies to the wrong side, so we can't net do that 727 00:45:58,780 --> 00:46:00,910 without ATP or energy input. 728 00:46:00,910 --> 00:46:04,100 And it turns out this is true for other sugars as well. 729 00:46:04,100 --> 00:46:08,710 And so you need energy input to add phosphate to the sugars. 730 00:46:11,350 --> 00:46:15,820 Plenty of energy input from glucose oxidation, 731 00:46:15,820 --> 00:46:20,200 but we need a reaction where phosphate addition is coupled 732 00:46:20,200 --> 00:46:22,930 to another reaction that makes it favorable, 733 00:46:22,930 --> 00:46:26,970 and we have to do this without making ATP. 734 00:46:26,970 --> 00:46:28,680 And again, it illustrates, again, 735 00:46:28,680 --> 00:46:31,530 the biological energy is not just about ATP. 736 00:46:31,530 --> 00:46:34,760 At a deeper level It's something different. 737 00:46:34,760 --> 00:46:37,840 And so to really discuss this and understand it, 738 00:46:37,840 --> 00:46:40,420 I need to introduce two concepts that 739 00:46:40,420 --> 00:46:45,070 are going to come up again over and over again in this class 740 00:46:45,070 --> 00:46:47,440 and across metabolism. 741 00:46:47,440 --> 00:46:51,820 The first of these is a very high-level bioenergetic 742 00:46:51,820 --> 00:46:55,810 concept, although it's really an energetic concept, 743 00:46:55,810 --> 00:46:59,270 and it comes back to what we already talked about. 744 00:46:59,270 --> 00:47:02,980 So, we know burning wood is favorable. 745 00:47:06,150 --> 00:47:20,660 The CN H2O N plus oxygen going to CO2 plus water. 746 00:47:20,660 --> 00:47:26,060 That's burning wood, lots of energy released. 747 00:47:26,060 --> 00:47:28,500 Drew it up there for a single-glucose molecule 748 00:47:28,500 --> 00:47:31,130 and what the energy release the delta G0 749 00:47:31,130 --> 00:47:33,870 prime is for that reaction. 750 00:47:33,870 --> 00:47:35,520 Now I want to point out chemically 751 00:47:35,520 --> 00:47:39,480 what is going on in this reaction. 752 00:47:39,480 --> 00:47:42,000 Chemically what is happening for this 753 00:47:42,000 --> 00:47:47,190 to occur is that electrons from the carbon 754 00:47:47,190 --> 00:47:50,610 are being moved to the oxygen. You 755 00:47:50,610 --> 00:47:55,440 are changing the oxidation state of carbon and of oxygen 756 00:47:55,440 --> 00:47:59,640 in order to carry out this reaction. 757 00:47:59,640 --> 00:48:04,230 Oxygen is a better electron acceptor than carbon, 758 00:48:04,230 --> 00:48:07,110 and so transferring those electrons 759 00:48:07,110 --> 00:48:12,240 from the carbon to the oxygen is favorable. 760 00:48:12,240 --> 00:48:17,580 That is, in essence, what is going on in this very favorable 761 00:48:17,580 --> 00:48:21,570 reaction to burn wood. 762 00:48:21,570 --> 00:48:26,740 Let me illustrate that a bit more explicitly here. 763 00:48:26,740 --> 00:48:31,080 So the carbon-- most of the carbons in carbohydrates 764 00:48:31,080 --> 00:48:35,100 are alcohols. 765 00:48:35,100 --> 00:48:41,570 So here, you can call this our carbohydrate, 766 00:48:41,570 --> 00:48:45,630 with the exception of the ketone or the aldehyde 767 00:48:45,630 --> 00:48:48,000 if it's a ketose or an aldose. 768 00:48:48,000 --> 00:48:51,805 All the other carbons in the sugar are alcohols. 769 00:48:57,750 --> 00:48:59,800 All the other bonds there. 770 00:48:59,800 --> 00:49:09,430 And so if we oxidize that carbon-- 771 00:49:09,430 --> 00:49:13,090 that is, if we remove electrons from the carbon, 772 00:49:13,090 --> 00:49:13,990 how can we do that? 773 00:49:16,680 --> 00:49:26,250 So this here generates this H- hydride ion. 774 00:49:26,250 --> 00:49:29,180 This is, in essence, two electrons 775 00:49:29,180 --> 00:49:31,070 that we are removing from the carbon. 776 00:49:39,470 --> 00:49:41,030 That gives us a ketone. 777 00:49:44,950 --> 00:49:48,510 So if we oxidize the alcohol and we remove two electrons, 778 00:49:48,510 --> 00:49:51,930 we get the ketone. 779 00:49:51,930 --> 00:49:54,855 We could oxidize this ketone further. 780 00:49:59,110 --> 00:50:03,060 That will give us the carboxylic acid. 781 00:50:03,060 --> 00:50:08,945 If we oxidize it even further, now we get CO2. 782 00:50:14,130 --> 00:50:20,640 So, moving in this direction, this is oxidation. 783 00:50:24,390 --> 00:50:27,600 Transferring electrons from the carbon to the oxygen 784 00:50:27,600 --> 00:50:30,390 to go in this oxidation direction, that 785 00:50:30,390 --> 00:50:32,850 is glucose oxidation is what's happening 786 00:50:32,850 --> 00:50:35,130 when we're burning wood. 787 00:50:35,130 --> 00:50:37,320 It's what happens when we burn glucose. 788 00:50:37,320 --> 00:50:38,415 Energy is released. 789 00:50:48,200 --> 00:50:57,980 This is largely what catabolism is about in biological systems. 790 00:50:57,980 --> 00:51:00,650 Now then reasons, then, that if we're 791 00:51:00,650 --> 00:51:05,150 going to move in the opposite direction, so-called reduction, 792 00:51:05,150 --> 00:51:14,060 that is going in this direction. 793 00:51:14,060 --> 00:51:14,930 Reduction. 794 00:51:17,740 --> 00:51:29,240 That's largely energy storage or anabolism in metabolism. 795 00:51:29,240 --> 00:51:34,160 We are storing energy that we can burn later. 796 00:51:34,160 --> 00:51:38,540 And of course, what's the more extreme version of this? 797 00:51:38,540 --> 00:51:41,600 Well, what if we add two more electrons to the carbon going 798 00:51:41,600 --> 00:51:43,380 in this direction? 799 00:51:43,380 --> 00:51:45,090 Well, what do we end up with? 800 00:51:45,090 --> 00:51:53,450 Well, now we end up with the saturated carbon. 801 00:51:53,450 --> 00:51:57,530 more reduced than the alcohol is the fully saturated carbon. 802 00:51:57,530 --> 00:52:00,260 You will see later that this is what fat is. 803 00:52:00,260 --> 00:52:02,810 You saw that in some of the earlier lectures. 804 00:52:02,810 --> 00:52:05,330 It's also what gasoline is. 805 00:52:05,330 --> 00:52:06,200 What's gasoline? 806 00:52:06,200 --> 00:52:10,010 It's fully saturated hydrocarbons that we then 807 00:52:10,010 --> 00:52:14,060 burn to CO2 and derive energy. 808 00:52:14,060 --> 00:52:18,230 Just like burning wood, burning gasoline all in one step, 809 00:52:18,230 --> 00:52:21,620 oxidizing the gasoline gives you energy. 810 00:52:21,620 --> 00:52:23,420 There's more energy in gasoline. 811 00:52:23,420 --> 00:52:25,610 You can release more energy per weight 812 00:52:25,610 --> 00:52:28,310 from gasoline, from fully-saturated hydrocarbons 813 00:52:28,310 --> 00:52:30,170 than you can from wood. 814 00:52:30,170 --> 00:52:31,580 Same thing happening here. 815 00:52:31,580 --> 00:52:33,410 What has more calories in your food? 816 00:52:33,410 --> 00:52:38,660 Everyone knows fat has more calories per weight than sugar. 817 00:52:38,660 --> 00:52:42,570 It's because the more reduced our carbon is, 818 00:52:42,570 --> 00:52:47,810 the more energy it stores, and as we oxidize that carbon, that 819 00:52:47,810 --> 00:52:51,400 is what releases the energy. 820 00:52:51,400 --> 00:52:57,700 And so energy transduction in biological systems-- 821 00:52:57,700 --> 00:52:59,735 and actually, in non-biological systems, 822 00:52:59,735 --> 00:53:02,110 as I just illustrated with the wood and gasoline example, 823 00:53:02,110 --> 00:53:04,450 but definitely in biological systems, 824 00:53:04,450 --> 00:53:09,370 is largely about oxidation and reduction reactions, 825 00:53:09,370 --> 00:53:14,570 and you are going to see this coming up over and over again. 826 00:53:14,570 --> 00:53:19,790 Now, based on what I just said, the real magic, if you will, 827 00:53:19,790 --> 00:53:26,020 of glycolysis can be further refined to say that what 828 00:53:26,020 --> 00:53:31,420 glycolysis does is it couples the favorable oxidation 829 00:53:31,420 --> 00:53:38,050 of carbon with reactions that allow phosphate additions 830 00:53:38,050 --> 00:53:40,780 and production of intermediates, like PEP 831 00:53:40,780 --> 00:53:45,490 and 1,3-Bisphosphoglycerate, where synthesis of ATP is 832 00:53:45,490 --> 00:53:51,190 favored despite the high ATP-ADP ratio in cells. 833 00:53:51,190 --> 00:53:53,800 If you think about it, that process 834 00:53:53,800 --> 00:53:56,800 then allows you to keep that ATP-ADP ratio 835 00:53:56,800 --> 00:53:58,810 in the range where it can then be 836 00:53:58,810 --> 00:54:01,510 useful for all the reasons we've been talking about now for two 837 00:54:01,510 --> 00:54:02,740 lectures. 838 00:54:02,740 --> 00:54:06,850 Allows the cell to couple that ATP-ADP ratio, that-- in ATP 839 00:54:06,850 --> 00:54:10,210 hydrolysis to otherwise carry out 840 00:54:10,210 --> 00:54:13,240 otherwise unfavorable reactions. 841 00:54:13,240 --> 00:54:13,960 OK. 842 00:54:13,960 --> 00:54:20,720 So, based on that, arguably the key, 843 00:54:20,720 --> 00:54:24,530 or at least a very important reaction in glycolysis, 844 00:54:24,530 --> 00:54:30,170 is the oxidation step which happens to add the phosphate 845 00:54:30,170 --> 00:54:34,260 and also happens to make 1,3-Bisphosphoglycerate, 846 00:54:34,260 --> 00:54:38,360 which we saw earlier can be used to drive ATP synthesis. 847 00:54:38,360 --> 00:54:40,460 And so that reaction is the following. 848 00:54:51,760 --> 00:54:54,360 So this molecule hopefully looks familiar to you 849 00:54:54,360 --> 00:54:57,090 from the carbohydrate lectures. 850 00:54:57,090 --> 00:55:09,310 This is D-glyceraldehyde 3-phosphate. 851 00:55:09,310 --> 00:55:11,200 I will abbreviate it frequently is 852 00:55:11,200 --> 00:55:14,830 G-3P for glyceraldehyde 3-phosphate, 853 00:55:14,830 --> 00:55:17,380 but it's D-glyceraldehyde 3-phosphate. 854 00:55:17,380 --> 00:55:19,420 Remember, it's a D, sugar, because the OH 855 00:55:19,420 --> 00:55:23,930 group is pointing to the right as we drew it this way. 856 00:55:23,930 --> 00:55:27,670 It's also an aldose because it's a aldehyde sugar, 857 00:55:27,670 --> 00:55:29,950 and it's phosphorylated on the 3 position-- 858 00:55:29,950 --> 00:55:33,520 remember the way we numbered sugars was starting 859 00:55:33,520 --> 00:55:34,390 at the carbonyl-- 860 00:55:34,390 --> 00:55:36,740 1, 2, 3. 861 00:55:36,740 --> 00:55:38,920 This is carbon-3, phosphorylation on the 3 862 00:55:38,920 --> 00:55:40,210 position. 863 00:55:40,210 --> 00:55:43,370 Glyceraldehyde 3-phosphate. 864 00:55:43,370 --> 00:55:44,060 OK. 865 00:55:44,060 --> 00:56:09,850 So, this step generates 1,3-Bisphosphoglycerate. 866 00:56:09,850 --> 00:56:11,380 Well, to do this, there's actually 867 00:56:11,380 --> 00:56:14,720 two things that happened here. 868 00:56:14,720 --> 00:56:18,040 First we had to add the phosphate to this. 869 00:56:18,040 --> 00:56:20,320 It says two phosphates on it. bisphosphoglycerate, 870 00:56:20,320 --> 00:56:22,030 this has a single phosphate. 871 00:56:22,030 --> 00:56:25,630 So inorganic phosphate has to be added 872 00:56:25,630 --> 00:56:28,720 to generate that molecule. 873 00:56:28,720 --> 00:56:34,000 By the way, adding that phosphate delta G0 prime 874 00:56:34,000 --> 00:56:37,300 is positive plus 1.5 kcals per mole. 875 00:56:37,300 --> 00:56:41,440 That means even equilibrium, this reaction 876 00:56:41,440 --> 00:56:43,960 would lie to the left, of course, 877 00:56:43,960 --> 00:56:46,880 because delta G0 prime is positive. 878 00:56:46,880 --> 00:56:50,470 However, remember the next step downstream of this 879 00:56:50,470 --> 00:56:54,490 is the one shown over here where we do ATP synthesis. 880 00:56:54,490 --> 00:56:56,390 That step is very favorable. 881 00:56:56,390 --> 00:56:58,810 So this is an example where metabolism 882 00:56:58,810 --> 00:57:03,000 has coupled a very favorable step to a step that's 883 00:57:03,000 --> 00:57:03,870 less favorable. 884 00:57:03,870 --> 00:57:08,280 That can keep the 1,3-BPG levels low and pull the entire system 885 00:57:08,280 --> 00:57:12,700 forward, the metabolic trick we discussed in the last lecture. 886 00:57:12,700 --> 00:57:13,680 OK. 887 00:57:13,680 --> 00:57:15,810 You'll note the other thing that's happening here, 888 00:57:15,810 --> 00:57:18,810 other than adding that phosphate group, 889 00:57:18,810 --> 00:57:26,700 is that we've changed this aldehyde to a carboxylic acid. 890 00:57:26,700 --> 00:57:29,970 That is an oxidation reaction. 891 00:57:29,970 --> 00:57:32,970 Ketone to the acid is an oxidation reaction. 892 00:57:32,970 --> 00:57:37,540 I will illustrate over here this so you can see 893 00:57:37,540 --> 00:57:41,970 why it's an oxidation reaction. 894 00:57:41,970 --> 00:57:43,370 So here's our aldehyde. 895 00:57:43,370 --> 00:57:47,240 If we take electrons from the carbon 896 00:57:47,240 --> 00:57:55,160 and that generates this hydride ion to electrons, 897 00:57:55,160 --> 00:57:56,660 what are we left with? 898 00:57:56,660 --> 00:58:01,907 Well, we're left with this intermediate 899 00:58:01,907 --> 00:58:04,365 that will never exist with a positive charge on the carbon. 900 00:58:14,810 --> 00:58:18,380 Water, which, of course, is abundant in biological systems. 901 00:58:18,380 --> 00:58:19,250 And then come-- 902 00:58:22,510 --> 00:58:24,100 OK. 903 00:58:24,100 --> 00:58:25,960 And it basically illustrates that as I 904 00:58:25,960 --> 00:58:30,490 go from the aldehyde to the acid, of course, 905 00:58:30,490 --> 00:58:33,040 I make a proton and a hydride ion, 906 00:58:33,040 --> 00:58:36,280 but really, I have changed the oxidation state of the carbon 907 00:58:36,280 --> 00:58:40,330 from the ketone to the acid state. 908 00:58:40,330 --> 00:58:45,460 Two electrons are lost there, is shown as that hydride ion. 909 00:58:45,460 --> 00:58:47,110 OK. 910 00:58:47,110 --> 00:58:48,950 So, what does that mean? 911 00:58:48,950 --> 00:58:52,690 Well, that means that we have to maintain that balance 912 00:58:52,690 --> 00:58:55,640 in this reaction as well. 913 00:58:55,640 --> 00:58:59,230 So water is going to have to come in 914 00:58:59,230 --> 00:59:02,110 and a proton will be produced. 915 00:59:02,110 --> 00:59:05,080 But the key thing is we also generate 916 00:59:05,080 --> 00:59:12,300 two electrons, this hydride ion that have to go somewhere. 917 00:59:12,300 --> 00:59:19,110 Now, finding a place for those two electrons to go 918 00:59:19,110 --> 00:59:24,360 is what brings up the second high-level concept 919 00:59:24,360 --> 00:59:27,810 that I now need to spend some time discussing. 920 01:00:06,130 --> 01:00:08,260 And this second high-level concept 921 01:00:08,260 --> 01:00:15,190 that I need to introduce is the role of cofactors, 922 01:00:15,190 --> 01:00:18,730 and cofactors also is effectively 923 01:00:18,730 --> 01:00:26,230 the role of vitamins and what role 924 01:00:26,230 --> 01:00:31,130 that these things play in metabolism. 925 01:00:31,130 --> 01:00:36,075 Most vitamins are used to support metabolic reactions, 926 01:00:36,075 --> 01:00:37,700 and we're going to learn all about what 927 01:00:37,700 --> 01:00:40,430 many of the vitamins that you guys are familiar with reading 928 01:00:40,430 --> 01:00:42,800 the side of your cereal box actually 929 01:00:42,800 --> 01:00:46,190 do throughout the course. 930 01:00:46,190 --> 01:00:51,900 Now cofactors, as I said, often involve vitamins, 931 01:00:51,900 --> 01:01:02,200 are molecules that provide useful chemical groups that 932 01:01:02,200 --> 01:01:05,530 facilitate the reaction chemistries that 933 01:01:05,530 --> 01:01:07,390 are needed in metabolism. 934 01:01:10,110 --> 01:01:13,790 So they provide some useful chemical groups 935 01:01:13,790 --> 01:01:20,230 to facilitate some of the chemistries 936 01:01:20,230 --> 01:01:24,810 that we need to carry out metabolic reactions. 937 01:01:24,810 --> 01:01:44,530 They are, in general, in small non-stoichiometric quantities 938 01:01:44,530 --> 01:01:46,780 in order to carry out this function. 939 01:01:46,780 --> 01:01:47,830 What do I mean by that? 940 01:01:47,830 --> 01:01:51,700 Meaning that you can imagine that the cell will convert lots 941 01:01:51,700 --> 01:01:57,240 of glyceraldehyde 3-phosphate to 1,3-Bisphosphoglycerate, 942 01:01:57,240 --> 01:02:00,690 but the enzyme, you don't need one enzyme for every time you 943 01:02:00,690 --> 01:02:01,860 convert that reaction. 944 01:02:01,860 --> 01:02:04,770 The same enzyme can do it over and over and over again. 945 01:02:04,770 --> 01:02:06,660 Well, it turns out, cofactors are much more 946 01:02:06,660 --> 01:02:08,520 like enzymes in that respect. 947 01:02:08,520 --> 01:02:11,220 They need to be recycled in a way 948 01:02:11,220 --> 01:02:13,980 that they can catalyze the turnover of reaction 949 01:02:13,980 --> 01:02:15,960 many, many, many times, and it'll 950 01:02:15,960 --> 01:02:17,790 be much clearer what I mean by this when we 951 01:02:17,790 --> 01:02:20,070 get into some of the details. 952 01:02:20,070 --> 01:02:23,730 Now, the vitamin concept comes from the fact 953 01:02:23,730 --> 01:02:38,710 that often these cofactors or parts of the cofactors 954 01:02:38,710 --> 01:02:43,660 are not made by animals, not made by humans. 955 01:02:46,810 --> 01:02:49,600 If they're not made by us, but we 956 01:02:49,600 --> 01:02:52,270 need them to do our metabolism, well now we 957 01:02:52,270 --> 01:02:55,360 have to get them from the diet, and this is really 958 01:02:55,360 --> 01:02:56,830 the concept of vitamins. 959 01:02:56,830 --> 01:02:59,470 These are small things that we have 960 01:02:59,470 --> 01:03:02,140 to get in quantities from the diet, 961 01:03:02,140 --> 01:03:05,170 and it turns out they're very important to help us carry out 962 01:03:05,170 --> 01:03:07,630 the metabolism we do. 963 01:03:07,630 --> 01:03:09,550 As an aside, the vitamin industry 964 01:03:09,550 --> 01:03:11,380 is a very big business. 965 01:03:11,380 --> 01:03:14,980 Lots of unfounded claims out there. 966 01:03:14,980 --> 01:03:16,480 I'm not going to get into-- 967 01:03:16,480 --> 01:03:17,770 that can get very political. 968 01:03:17,770 --> 01:03:20,890 I'm just going to say that just know that more is not 969 01:03:20,890 --> 01:03:23,680 always better, and the goal for this class 970 01:03:23,680 --> 01:03:27,340 is really to understand what some of these vitamins 971 01:03:27,340 --> 01:03:30,130 actually do. 972 01:03:30,130 --> 01:03:31,300 OK. 973 01:03:31,300 --> 01:03:35,950 Now, the relevant cofactor for the reaction that we're talking 974 01:03:35,950 --> 01:03:41,080 about is a cofactor called nicotinamide adenine 975 01:03:41,080 --> 01:03:47,590 dinucleotide, which is always abbreviated NAD or NAD+. 976 01:03:47,590 --> 01:04:05,325 This stands for nicotinamide adenine dinucleotide. 977 01:04:05,325 --> 01:04:09,330 You see why we want to abbreviate that NAD. 978 01:04:09,330 --> 01:04:14,070 And basically what nicotinamide adenine dinucleotide is is it's 979 01:04:14,070 --> 01:04:17,640 a factor that can solve our problem of where 980 01:04:17,640 --> 01:04:21,810 to put these electrons in this oxidation reaction. 981 01:04:21,810 --> 01:04:26,140 That is, you can accept two electrons 982 01:04:26,140 --> 01:04:29,350 from a reaction like this one here 983 01:04:29,350 --> 01:04:36,370 and cycle to another form of the cofactor called NADH. 984 01:04:36,370 --> 01:04:37,240 All right. 985 01:04:37,240 --> 01:04:39,490 What is nicotinamide adenine dinucleotide? 986 01:04:39,490 --> 01:04:42,760 Well first, let's draw what it looks like. 987 01:05:48,232 --> 01:05:48,810 OK. 988 01:05:48,810 --> 01:05:51,660 Sorry it's squeeze down here a little bit. 989 01:05:51,660 --> 01:05:57,500 So this here is adenine. 990 01:05:57,500 --> 01:06:01,455 This group up here is nicotinamide. 991 01:06:06,460 --> 01:06:10,270 So if you look at this, this is a dinucleotide. 992 01:06:10,270 --> 01:06:14,710 And so down here, this, of course, is, from here down, 993 01:06:14,710 --> 01:06:16,660 is AMP. 994 01:06:16,660 --> 01:06:18,680 That phosphate is now over here. 995 01:06:18,680 --> 01:06:21,460 This is a separate nucleotide, where 996 01:06:21,460 --> 01:06:25,330 rather than having one of the AGCTU bases 997 01:06:25,330 --> 01:06:29,770 that you're used to from RNA and DNA, nicotinamide is the base. 998 01:06:29,770 --> 01:06:36,510 And so it's this AMP plus this nicotinamide 999 01:06:36,510 --> 01:06:40,410 base is a monophosphate, or a nicotinamide adenine 1000 01:06:40,410 --> 01:06:42,930 dinucleotide. 1001 01:06:42,930 --> 01:06:49,820 This, the nicotinamide group, is derived 1002 01:06:49,820 --> 01:06:53,840 from a vitamin called niacin. 1003 01:06:53,840 --> 01:06:55,670 And so from the side of your cereal box, 1004 01:06:55,670 --> 01:06:57,170 this is what niacin does. 1005 01:06:57,170 --> 01:07:01,310 It allows you to generate the nicotinamide group that's 1006 01:07:01,310 --> 01:07:04,670 part of this cofactor, nicotinamide adenine 1007 01:07:04,670 --> 01:07:06,770 dinucleotide. 1008 01:07:06,770 --> 01:07:10,700 Now, nicotinamide adenine dinucleotide 1009 01:07:10,700 --> 01:07:16,800 is useful because of what that nicotinamide group can do. 1010 01:07:16,800 --> 01:07:19,130 And so I'm not going to draw out the whole molecule, 1011 01:07:19,130 --> 01:07:19,950 but I'll show you. 1012 01:07:19,950 --> 01:07:27,960 So NAD+, which is the oxidized form of nicotinamide adenine 1013 01:07:27,960 --> 01:07:32,270 dinucleotide, is as I drew it up there. 1014 01:07:35,050 --> 01:07:38,930 So this here would be attached to the rest 1015 01:07:38,930 --> 01:07:40,880 of the dinucleotide. 1016 01:07:45,490 --> 01:07:48,880 So this is the oxidized form. 1017 01:07:48,880 --> 01:07:55,580 I can have-- here's my hydride ion, which, remember, 1018 01:07:55,580 --> 01:07:57,410 is two electrons. 1019 01:08:05,110 --> 01:08:08,070 If I carry out that chemistry to add those two electrons 1020 01:08:08,070 --> 01:08:26,479 to the nicotinamide group, you now end up 1021 01:08:26,479 --> 01:08:33,970 with the reduced form of nicotinamide adenine 1022 01:08:33,970 --> 01:08:36,580 dinucleotide NADH. 1023 01:08:36,580 --> 01:08:41,710 So the difference between NAD+ and NADH, it's the H, 1024 01:08:41,710 --> 01:08:44,710 but it's really the two electrons that were added 1025 01:08:44,710 --> 01:08:53,380 in adding that H. So it's oxidized form and reduced form. 1026 01:08:53,380 --> 01:08:57,760 So remember, I want to stress this again, at least in biology 1027 01:08:57,760 --> 01:08:59,920 we can't create or destroy matter. 1028 01:08:59,920 --> 01:09:01,810 You can do that in nuclear physics, 1029 01:09:01,810 --> 01:09:05,080 but we can't do that in biology. 1030 01:09:05,080 --> 01:09:08,729 And so that means that if we do an electron transfer like we 1031 01:09:08,729 --> 01:09:13,200 did in this reaction where we oxidized the aldehyde 1032 01:09:13,200 --> 01:09:16,080 in glyceraldehyde 3-phosphate to the acid 1033 01:09:16,080 --> 01:09:20,279 in 1,3-Bisphosphoglycerate, those electrons have to be 1034 01:09:20,279 --> 01:09:21,790 accounted for. 1035 01:09:21,790 --> 01:09:24,240 And so if one molecule is oxidized, 1036 01:09:24,240 --> 01:09:27,279 another one has to be reduced. 1037 01:09:27,279 --> 01:09:29,430 So redox reactions always-- that is, 1038 01:09:29,430 --> 01:09:31,859 redox, oxidation-reduction reactions, 1039 01:09:31,859 --> 01:09:34,470 always have to happen in pairs. 1040 01:09:34,470 --> 01:09:39,000 And so over there we have the aldehyde in glyceraldehyde 1041 01:09:39,000 --> 01:09:50,399 3-phosphate is oxidized to form the acid 1042 01:09:50,399 --> 01:09:52,299 in 1,3-Bisphosphoglycerate. 1043 01:09:55,150 --> 01:09:58,950 As part of that reaction, we can couple it such 1044 01:09:58,950 --> 01:10:03,780 that the nicotinamide group, which is oxidized in NAD, 1045 01:10:03,780 --> 01:10:10,580 can be reduced to the nicotinamide group that 1046 01:10:10,580 --> 01:10:12,077 is found in NADH. 1047 01:10:14,780 --> 01:10:20,540 So that means we can draw this in here, 1048 01:10:20,540 --> 01:10:34,190 is that having that cofactor coupled to this reaction 1049 01:10:34,190 --> 01:10:40,720 now allows us to fix the redox problem of this reaction. 1050 01:10:40,720 --> 01:10:45,730 Now this reaction here is catalyzed 1051 01:10:45,730 --> 01:10:56,925 by an enzyme called glycerol 3-phosphate dehydrogenase. 1052 01:10:56,925 --> 01:10:58,300 I'll draw that out in the second. 1053 01:11:35,930 --> 01:11:42,010 Often abbreviated GAPDH, the loading control 1054 01:11:42,010 --> 01:11:45,190 in all of your western blots, is the enzyme GAPDH, 1055 01:11:45,190 --> 01:11:48,630 glyceraldehyde phosphate dehydrogenase. 1056 01:11:48,630 --> 01:11:53,890 That is the enzyme that carries out that reaction. 1057 01:11:53,890 --> 01:11:55,710 Now notice, the name fits. 1058 01:11:55,710 --> 01:12:00,120 It's a dehydrogenase, it's removing a hydrogen, 1059 01:12:00,120 --> 01:12:03,690 removing two electrons as a hydride ion, 1060 01:12:03,690 --> 01:12:05,550 but it's really-- what's important here 1061 01:12:05,550 --> 01:12:08,960 is the electrons moving, not the hydrogen itself. 1062 01:12:08,960 --> 01:12:11,700 So in that way it's a little bit misleading. 1063 01:12:11,700 --> 01:12:15,600 And you will see that in general, dehydrogenases 1064 01:12:15,600 --> 01:12:19,470 are classes of enzymes that catalyze 1065 01:12:19,470 --> 01:12:23,110 oxidation-reduction reactions, and as a result, 1066 01:12:23,110 --> 01:12:27,090 often involve NAD/NADH as cofactors 1067 01:12:27,090 --> 01:12:33,560 because they facilitate those electron transfer reactions. 1068 01:12:33,560 --> 01:12:34,790 OK. 1069 01:12:34,790 --> 01:12:36,860 So now we're able to describe how 1070 01:12:36,860 --> 01:12:41,670 GAPDH works in great detail. 1071 01:12:41,670 --> 01:12:47,520 And so the chemistry of GAPDH works as follows. 1072 01:12:47,520 --> 01:12:52,420 And so in the active site of GAPDH, 1073 01:12:52,420 --> 01:12:54,420 there's a cystine residue. 1074 01:12:54,420 --> 01:12:58,570 That cystine residue has a sulfur shown here. 1075 01:12:58,570 --> 01:13:03,900 Also bound near the active site is in NAD molecule 1076 01:13:03,900 --> 01:13:07,020 to catalyze the reaction shown. 1077 01:13:07,020 --> 01:13:11,400 That NAD has to be in the oxidized state, so it's NAD+. 1078 01:13:11,400 --> 01:13:18,300 And so glyceraldehyde 3-phosphate binds 1079 01:13:18,300 --> 01:13:19,320 in the active site. 1080 01:13:27,620 --> 01:13:29,660 There's glyceraldehyde 3-phosphate. 1081 01:13:33,710 --> 01:13:39,850 By the way, I will show you how many reactions in metabolism 1082 01:13:39,850 --> 01:13:41,800 work chemically. 1083 01:13:41,800 --> 01:13:45,790 Obviously we don't have time in this class, an overview class 1084 01:13:45,790 --> 01:13:48,970 to go into all the great chemical details of what's 1085 01:13:48,970 --> 01:13:51,465 going on and exactly how everything works, 1086 01:13:51,465 --> 01:13:52,840 but I'll at least try to give you 1087 01:13:52,840 --> 01:13:54,490 a flavor of some of the chemistry that 1088 01:13:54,490 --> 01:13:56,930 happens throughout the course. 1089 01:13:56,930 --> 01:13:57,430 All right. 1090 01:13:57,430 --> 01:13:58,750 So once you have, then-- 1091 01:14:19,900 --> 01:14:20,400 OK. 1092 01:14:20,400 --> 01:14:22,530 So now you have this intermediate bound 1093 01:14:22,530 --> 01:14:25,860 into the enzyme active site. 1094 01:14:25,860 --> 01:14:33,460 You can now carry out the oxidation of that carbon. 1095 01:14:33,460 --> 01:14:39,810 So these are two electrons being removed as a hydride ion. 1096 01:14:39,810 --> 01:14:43,350 They can be transferred to NAD in the active site. 1097 01:14:43,350 --> 01:14:46,500 That generates NADH by the exact chemistry 1098 01:14:46,500 --> 01:14:47,940 that I just showed you. 1099 01:15:04,690 --> 01:15:05,950 OK. 1100 01:15:05,950 --> 01:15:11,440 That NADH now needs to be exchanged out 1101 01:15:11,440 --> 01:15:18,490 or the enzyme will not be able to catalyze 1102 01:15:18,490 --> 01:15:21,855 the next series of reactions, and that NADH will then 1103 01:15:21,855 --> 01:15:23,230 go somewhere else, and of course, 1104 01:15:23,230 --> 01:15:26,050 has to be cycled back to NAD, but that doesn't happen 1105 01:15:26,050 --> 01:15:28,000 in this reaction, per se. 1106 01:15:58,030 --> 01:15:59,550 OK. 1107 01:15:59,550 --> 01:16:08,030 Next, this here, you'll notice, is that by the way 1108 01:16:08,030 --> 01:16:11,690 this chemistry worked, we formed this thioester bond 1109 01:16:11,690 --> 01:16:13,500 in the active site. 1110 01:16:13,500 --> 01:16:16,580 This is another thing that you will see over and over again 1111 01:16:16,580 --> 01:16:18,020 in metabolism. 1112 01:16:18,020 --> 01:16:21,060 This sulfur in the thioester bond is a good leaving group, 1113 01:16:21,060 --> 01:16:24,410 and so it's really setting up a situation that will now help 1114 01:16:24,410 --> 01:16:27,570 with the phosphate addition. 1115 01:16:27,570 --> 01:16:30,920 So here, I'll draw out inorganic phosphate. 1116 01:16:40,830 --> 01:16:49,970 And that, of course, will give us the identical enzyme active 1117 01:16:49,970 --> 01:16:58,310 site that we started with plus 1,3-Bisphosphoglycerate. 1118 01:17:03,990 --> 01:17:14,070 And that 1,3-Bisphosphoglycerate can now be coupled to ATP 1119 01:17:14,070 --> 01:17:18,900 synthesis to make 3-phosphoglycerate. 1120 01:17:18,900 --> 01:17:23,550 And so you can see, in essence, what this reaction has done is 1121 01:17:23,550 --> 01:17:28,950 that it has coupled oxidation of the aldehyde to the acid, 1122 01:17:28,950 --> 01:17:32,610 the aldehyde in 3-phosphate to the acid 1123 01:17:32,610 --> 01:17:35,700 in 1,3-Bisphosphoglycerate, which can then do 1124 01:17:35,700 --> 01:17:38,920 phosphorylation of ADP to make ATP. 1125 01:17:38,920 --> 01:17:47,500 So in essence, this is oxidative phosphorylation. 1126 01:17:52,700 --> 01:17:55,060 Now I realize in high school or in other classes, 1127 01:17:55,060 --> 01:17:57,850 oxidative phosphorylation means something different to you, 1128 01:17:57,850 --> 01:18:00,280 and of course, we will discuss the process that 1129 01:18:00,280 --> 01:18:02,950 is called oxidative phosphorylation in great detail 1130 01:18:02,950 --> 01:18:04,880 later in this course. 1131 01:18:04,880 --> 01:18:07,360 But I want to point out that the chemistry that's actually 1132 01:18:07,360 --> 01:18:12,430 happening here in glycolysis is also oxidative phosphorylation. 1133 01:18:12,430 --> 01:18:17,890 It's basically how you coupled this favorable carbon oxidation 1134 01:18:17,890 --> 01:18:20,620 that's occurring at this GAPDH step 1135 01:18:20,620 --> 01:18:25,060 in a way that allows you to synthesize ATP 1136 01:18:25,060 --> 01:18:30,580 at a high ATP-ADP ratio, which in the end will allow cells 1137 01:18:30,580 --> 01:18:34,350 to do otherwise unfavorable things. 1138 01:18:34,350 --> 01:18:35,700 OK. 1139 01:18:35,700 --> 01:18:42,900 Now we're ready to discuss these reactions, the GAPDH reaction, 1140 01:18:42,900 --> 01:18:45,990 the pyruvate kinase reaction, the phosphoglycerate kinase 1141 01:18:45,990 --> 01:18:49,680 reaction, and how they fit into glycolysis 1142 01:18:49,680 --> 01:18:54,300 as a metabolic pathway in a way that allows cells to use 1143 01:18:54,300 --> 01:18:57,120 glucose metabolism-- that is, the breakdown of glucose, 1144 01:18:57,120 --> 01:19:01,350 the burning of glucose as a way to get energy. 1145 01:19:01,350 --> 01:19:06,210 And that pathway is, of course, glycolysis or glucose lysis 1146 01:19:06,210 --> 01:19:08,520 that we mentioned earlier. 1147 01:19:08,520 --> 01:19:12,420 Glycolysis is a very ancient and ubiquitous pathway. 1148 01:19:12,420 --> 01:19:15,630 It's used by essentially all life on Earth 1149 01:19:15,630 --> 01:19:21,200 and probably has been for at least 2 to 3 billion years. 1150 01:19:21,200 --> 01:19:23,780 Glycolysis, I guess, as a pathway was, 1151 01:19:23,780 --> 01:19:27,860 quote-unquote, "discovered" mid-19th century 1152 01:19:27,860 --> 01:19:30,530 by Louis Pasteur, and Louis Pasteur, 1153 01:19:30,530 --> 01:19:34,670 of course, described life, microorganisms 1154 01:19:34,670 --> 01:19:38,420 as being responsible for the process of fermentation. 1155 01:19:38,420 --> 01:19:42,980 That is, conversion of glucose into alcohol, something 1156 01:19:42,980 --> 01:19:45,290 many college students are interested in, as well 1157 01:19:45,290 --> 01:19:48,950 as other organic acids. 1158 01:19:48,950 --> 01:19:52,310 And of course, fermentation to make alcohol 1159 01:19:52,310 --> 01:19:57,740 or to store other types of organic acids 1160 01:19:57,740 --> 01:19:59,870 has been used in food preservation 1161 01:19:59,870 --> 01:20:03,560 for centuries, which is really why Pasteur's discoveries were 1162 01:20:03,560 --> 01:20:06,890 so impactful at the time. 1163 01:20:06,890 --> 01:20:08,600 Now even though Pasteur discovered this, 1164 01:20:08,600 --> 01:20:11,330 he didn't really understand chemically how it worked, 1165 01:20:11,330 --> 01:20:14,670 and it actually took decades to figure that out. 1166 01:20:14,670 --> 01:20:17,360 And when it was finally figured out and described 1167 01:20:17,360 --> 01:20:19,670 as the pathway called glycolysis, 1168 01:20:19,670 --> 01:20:23,510 this was done by two chemists, two chemists in Germany, Embden 1169 01:20:23,510 --> 01:20:24,710 and Meyerhof. 1170 01:20:24,710 --> 01:20:28,040 And basically what they did is they pieced together 1171 01:20:28,040 --> 01:20:31,430 several enzymatic or chemical activities that 1172 01:20:31,430 --> 01:20:35,570 have been purified from cell lysates mostly from yeast 1173 01:20:35,570 --> 01:20:39,290 and used those to build a pathway that described 1174 01:20:39,290 --> 01:20:43,370 chemically how you could start with glucose 1175 01:20:43,370 --> 01:20:47,030 and chemically break down that glucose in a way that made 1176 01:20:47,030 --> 01:20:50,130 sense in this fermentation pathway, 1177 01:20:50,130 --> 01:20:53,750 and that is why glycolysis is sometimes called 1178 01:20:53,750 --> 01:20:56,780 the Embden-Meyerhof pathway. 1179 01:21:32,910 --> 01:21:35,820 Now, glycolysis does not completely 1180 01:21:35,820 --> 01:21:38,940 convert glucose to CO2. 1181 01:21:38,940 --> 01:21:44,310 Instead, what glycolysis does is it converts glucose-- 1182 01:21:54,400 --> 01:21:58,540 so I will draw here in the pyranose form. 1183 01:21:58,540 --> 01:22:05,960 It converts glucose by a number of steps 1184 01:22:05,960 --> 01:22:12,890 into two molecules of the organic acid pyruvate, which, 1185 01:22:12,890 --> 01:22:19,040 of course, was the product of that pyruvate kinase reaction 1186 01:22:19,040 --> 01:22:20,495 that we showed earlier. 1187 01:22:29,080 --> 01:22:34,450 Note that the fermentation that Louis Pasteur described 1188 01:22:34,450 --> 01:22:39,220 was further metabolism of that pyruvate into something else. 1189 01:22:39,220 --> 01:22:50,840 In the case of yeast, it was ethanol or ethyl alcohol, 1190 01:22:50,840 --> 01:22:51,920 or something else. 1191 01:22:51,920 --> 01:23:04,210 The fermentative product in mammals 1192 01:23:04,210 --> 01:23:08,770 is this organic acid lactate. 1193 01:23:08,770 --> 01:23:11,500 And what we will see next time is 1194 01:23:11,500 --> 01:23:15,280 that this fermentation of pyruvate 1195 01:23:15,280 --> 01:23:18,200 into one of these other molecules 1196 01:23:18,200 --> 01:23:22,010 ends up being an alternative to the further oxidation 1197 01:23:22,010 --> 01:23:26,000 of pyruvate to CO2 which requires oxygen, 1198 01:23:26,000 --> 01:23:30,050 and the reason oxidizing pyruvate to CO2 1199 01:23:30,050 --> 01:23:33,230 requires oxygen is because ultimately we 1200 01:23:33,230 --> 01:23:37,820 have to regenerate that NADH we made in glycolysis to allow 1201 01:23:37,820 --> 01:23:41,780 that cofactor to cycle and glycolysis to keep moving. 1202 01:23:41,780 --> 01:23:45,930 Fermentation gives us an alternative way 1203 01:23:45,930 --> 01:23:49,290 to do this, which we'll discuss in great detail 1204 01:23:49,290 --> 01:23:51,180 in the next lecture. 1205 01:23:51,180 --> 01:23:56,570 But first I want to focus on glycolysis 1206 01:23:56,570 --> 01:23:59,690 and what we can describe next time as really how 1207 01:23:59,690 --> 01:24:03,020 we can build a pathway to turn glucose into pyruvate. 1208 01:24:03,020 --> 01:24:06,170 This glycolysis, this Embden-Meyerhof pathway, 1209 01:24:06,170 --> 01:24:08,450 and some of the details of that pathway 1210 01:24:08,450 --> 01:24:11,820 are shown here on this slide. 1211 01:24:11,820 --> 01:24:14,720 And this is where we'll start off the next lecture, 1212 01:24:14,720 --> 01:24:19,910 discussing how each of these steps in glycolysis function 1213 01:24:19,910 --> 01:24:26,120 in a way that allow a pathway to generate phosphoenolpyruvate, 1214 01:24:26,120 --> 01:24:30,050 1,3-Bisphosphoglycerate, incorporate this GAPDH 1215 01:24:30,050 --> 01:24:34,220 reaction, and do so in a way that's overall energetically 1216 01:24:34,220 --> 01:24:37,640 favorable to allow the cell to couple this oxidation 1217 01:24:37,640 --> 01:24:42,710 of glucose to keeping ATP-ADP ratio in the right range 1218 01:24:42,710 --> 01:24:46,720 to support other unfavorable functions in the cell. 1219 01:24:46,720 --> 01:24:48,610 OK, thanks.