1 00:00:15,757 --> 00:00:17,590 PROFESSOR: So what are we going to do today? 2 00:00:17,590 --> 00:00:21,180 So, today we're going to continue with amino acids, 3 00:00:21,180 --> 00:00:22,980 peptides, and proteins. 4 00:00:22,980 --> 00:00:28,140 And I want to talk about a different protein 5 00:00:28,140 --> 00:00:32,280 variant that is the causative, the cause of sickle cell 6 00:00:32,280 --> 00:00:32,850 anemia. 7 00:00:32,850 --> 00:00:35,460 And it's a very interesting structural issue. 8 00:00:35,460 --> 00:00:39,310 But let me very briefly recap what we did last time 9 00:00:39,310 --> 00:00:40,800 and then talk to you a little bit 10 00:00:40,800 --> 00:00:45,750 about a process known as denaturation. 11 00:00:45,750 --> 00:00:50,550 So last time, we discussed how the primary sequence 12 00:00:50,550 --> 00:00:55,050 of a polypeptide chain defines its folded structure. 13 00:00:55,050 --> 00:00:56,970 The folded structure is put in place 14 00:00:56,970 --> 00:01:01,050 with secondary and tertiary interactions, 15 00:01:01,050 --> 00:01:03,210 non-covalent interactions. 16 00:01:03,210 --> 00:01:07,950 Secondary just amongst backbone and its tertiary sort 17 00:01:07,950 --> 00:01:11,520 of everything else, even including backbone amides, 18 00:01:11,520 --> 00:01:14,650 but either with water, or a side chain, and so on. 19 00:01:14,650 --> 00:01:18,060 And then there are some proteins that dissociate 20 00:01:18,060 --> 00:01:19,980 into quaternary structure. 21 00:01:24,580 --> 00:01:28,650 So these monomer subunits, as they would be called-- 22 00:01:28,650 --> 00:01:31,920 and I'm going to depict this as a closed circle or an open 23 00:01:31,920 --> 00:01:32,730 circle-- 24 00:01:32,730 --> 00:01:35,220 may form dimers of some kind. 25 00:01:35,220 --> 00:01:37,020 The dimers may be heterodimers. 26 00:01:39,870 --> 00:01:42,880 Or they may be homodimers. 27 00:01:42,880 --> 00:01:46,220 Or you could form trimers, tetramers, and so on. 28 00:01:46,220 --> 00:01:48,700 And when we talk about hemoglobin, 29 00:01:48,700 --> 00:01:52,390 which is the protein that gets, that has a problem-- 30 00:01:52,390 --> 00:01:54,640 that is the cause of sickle cell anemia, 31 00:01:54,640 --> 00:01:58,640 you'll see that that is a heterotetrameric protein. 32 00:01:58,640 --> 00:02:00,520 So in this sort of rendition, you 33 00:02:00,520 --> 00:02:06,370 would kind of draw it like this where there are four subunits. 34 00:02:06,370 --> 00:02:08,860 Two are of one flavor and two are of the other. 35 00:02:08,860 --> 00:02:12,370 And that's the quaternary structure of hemoglobin. 36 00:02:12,370 --> 00:02:14,620 Now proteins fold. 37 00:02:14,620 --> 00:02:17,340 There are weak forces that are holding them together. 38 00:02:17,340 --> 00:02:19,240 But there's a lot of weak forces. 39 00:02:19,240 --> 00:02:22,750 But if you subject a protein to various treatments that 40 00:02:22,750 --> 00:02:26,140 may break up those weak forces, the protein 41 00:02:26,140 --> 00:02:28,810 will undergo a process of denaturation. 42 00:02:28,810 --> 00:02:31,210 So can anyone think of what kinds of things 43 00:02:31,210 --> 00:02:33,790 would cause protein DNA denaturation? 44 00:02:33,790 --> 00:02:34,517 Yes. 45 00:02:34,517 --> 00:02:35,350 AUDIENCE: Some heat. 46 00:02:35,350 --> 00:02:39,910 PROFESSOR: Heat is a bad one, is a serious one, obviously. 47 00:02:39,910 --> 00:02:42,158 And heat-- yes, I'll write them all down. 48 00:02:42,158 --> 00:02:42,700 What's yours? 49 00:02:42,700 --> 00:02:43,887 AUDIENCE: pH. 50 00:02:43,887 --> 00:02:44,470 PROFESSOR: pH. 51 00:02:44,470 --> 00:02:47,080 So pH. 52 00:02:47,080 --> 00:02:48,700 Acidity. 53 00:02:48,700 --> 00:02:50,100 Basicity. 54 00:02:50,100 --> 00:02:54,430 And we'll talk about why those things cause changes. 55 00:02:54,430 --> 00:02:55,900 Any other thoughts? 56 00:02:55,900 --> 00:02:56,658 Yes? 57 00:02:56,658 --> 00:02:58,800 AUDIENCE: [INAUDIBLE] 58 00:02:58,800 --> 00:03:00,250 PROFESSOR: Oh. 59 00:03:00,250 --> 00:03:00,750 Yeah. 60 00:03:00,750 --> 00:03:04,785 So for example, salt. Organic solvents. 61 00:03:13,650 --> 00:03:15,480 And a process that a lot of people 62 00:03:15,480 --> 00:03:18,210 don't necessarily think about, but as engineers some of you 63 00:03:18,210 --> 00:03:20,130 will, is shear forces. 64 00:03:20,130 --> 00:03:27,210 So if you're shooting a protein through a very narrow tubing 65 00:03:27,210 --> 00:03:29,670 and there's high shear forces, those who will also 66 00:03:29,670 --> 00:03:31,320 denature nature proteins. 67 00:03:31,320 --> 00:03:33,120 So with heat, it's very clear. 68 00:03:33,120 --> 00:03:35,370 You're going to break those weak bonds. 69 00:03:35,370 --> 00:03:38,790 And then they can either reform. 70 00:03:38,790 --> 00:03:42,990 Or if you go to too high heat, the unfolded protein 71 00:03:42,990 --> 00:03:45,330 starts to form aggregates. 72 00:03:45,330 --> 00:03:48,630 And anyone who has ever scrambled an egg 73 00:03:48,630 --> 00:03:51,240 knows that that is an irreversible process. 74 00:03:51,240 --> 00:03:53,930 You don't get to cram the egg back into the shell. 75 00:03:53,930 --> 00:03:55,450 It's not the same anymore. 76 00:03:55,450 --> 00:03:57,450 Because what you're doing when you're scrambling 77 00:03:57,450 --> 00:04:01,390 eggs is denaturing proteins through heat treatment. 78 00:04:01,390 --> 00:04:02,530 So that's what heat does. 79 00:04:02,530 --> 00:04:04,210 It breaks the forces. 80 00:04:04,210 --> 00:04:08,220 The proteins stretch out into their denatured state. 81 00:04:08,220 --> 00:04:11,070 And instead of refolding to a compact structure, 82 00:04:11,070 --> 00:04:13,260 they just start aggregating with each other. 83 00:04:13,260 --> 00:04:15,740 And that's pretty much irreversible. 84 00:04:15,740 --> 00:04:17,279 pH is interesting. 85 00:04:17,279 --> 00:04:20,950 Why would pH break up at low temperature? 86 00:04:20,950 --> 00:04:24,420 Why would pH cause changes? 87 00:04:24,420 --> 00:04:25,113 Yeah. 88 00:04:25,113 --> 00:04:27,955 AUDIENCE: [INAUDIBLE] amino acids have a certain structure. 89 00:04:27,955 --> 00:04:30,372 So they're either protonated or deprotonated, then the pH, 90 00:04:30,372 --> 00:04:31,230 that would change. 91 00:04:31,230 --> 00:04:31,813 PROFESSOR: OK. 92 00:04:31,813 --> 00:04:33,330 So pH, perfect. 93 00:04:33,330 --> 00:04:36,180 So pH will change the charge states 94 00:04:36,180 --> 00:04:38,030 of many of your sight chains. 95 00:04:38,030 --> 00:04:39,900 And once you've changed it, you might 96 00:04:39,900 --> 00:04:42,360 have had a lovely electrostatic interaction. 97 00:04:42,360 --> 00:04:45,300 But then you go and protonate the carboxylic acid. 98 00:04:45,300 --> 00:04:48,480 And it can't form-- in fact, it wants the form, 99 00:04:48,480 --> 00:04:51,720 it wants to break apart as opposed to come together. 100 00:04:51,720 --> 00:04:54,600 So that is changing charged state, 101 00:04:54,600 --> 00:04:57,180 which causes denaturation. 102 00:04:57,180 --> 00:04:58,890 Salts and organics. 103 00:04:58,890 --> 00:05:01,680 For example, they may make interactions 104 00:05:01,680 --> 00:05:03,340 with parts of the protein. 105 00:05:03,340 --> 00:05:06,240 For example, organics, organic molecules 106 00:05:06,240 --> 00:05:10,110 may slip into a hydrophobic core and break them up. 107 00:05:10,110 --> 00:05:11,380 Just push them apart. 108 00:05:11,380 --> 00:05:12,510 They want to be there. 109 00:05:12,510 --> 00:05:15,870 And then too much of a high concentration 110 00:05:15,870 --> 00:05:19,120 of an organic solvent that is miserable with water. 111 00:05:19,120 --> 00:05:22,380 And we would say ethanol, acetonitrile, DMSO. 112 00:05:22,380 --> 00:05:24,030 But you don't need to worry about too 113 00:05:24,030 --> 00:05:25,350 much of which details. 114 00:05:25,350 --> 00:05:28,310 Well actually, once you get above 10% or so, 115 00:05:28,310 --> 00:05:32,170 we'll just start denaturing proteins, sometimes reversibly 116 00:05:32,170 --> 00:05:34,420 but often irreversibly. 117 00:05:34,420 --> 00:05:38,460 So this is very important to know that proteins are stable, 118 00:05:38,460 --> 00:05:40,650 but you've got to treat them nicely. 119 00:05:40,650 --> 00:05:43,350 There are some human diseases that 120 00:05:43,350 --> 00:05:46,980 are a result of misfolded or aggregated proteins. 121 00:05:46,980 --> 00:05:49,680 So for example, all the prion diseases 122 00:05:49,680 --> 00:05:52,140 are proteins gone bad, pretty much, 123 00:05:52,140 --> 00:05:54,370 where they are not in a folded structure anymore, 124 00:05:54,370 --> 00:05:57,210 but they are in aggregates that cause problems 125 00:05:57,210 --> 00:06:00,510 with cellular processes and toxicity. 126 00:06:00,510 --> 00:06:02,940 So Alzheimer's disease. 127 00:06:02,940 --> 00:06:04,050 Mad cow disease. 128 00:06:04,050 --> 00:06:07,200 A lot of those are neurologic disorders 129 00:06:07,200 --> 00:06:11,550 caused by poorly folded or very misfolded proteins, 130 00:06:11,550 --> 00:06:12,730 for example. 131 00:06:12,730 --> 00:06:16,170 So these are the things we talked about last time 132 00:06:16,170 --> 00:06:19,170 with respect to the flux from primary to secondary, 133 00:06:19,170 --> 00:06:22,090 to tertiary to quaternary. 134 00:06:22,090 --> 00:06:25,740 And that's a perfect time for me to introduce to you 135 00:06:25,740 --> 00:06:27,400 what we'll talk about today. 136 00:06:27,400 --> 00:06:31,140 So last time we talked about structural proteins. 137 00:06:31,140 --> 00:06:33,990 And I showed you how collagen, just 138 00:06:33,990 --> 00:06:38,310 with a simple defect, changing a glycine an alanine in one 139 00:06:38,310 --> 00:06:43,560 of its subunits, really alters the quaternary structure 140 00:06:43,560 --> 00:06:46,620 of the protein to make very weak collagen 141 00:06:46,620 --> 00:06:49,380 that's no longer supportive of bone strength. 142 00:06:49,380 --> 00:06:51,360 But what I'm going to talk to you about today 143 00:06:51,360 --> 00:06:53,850 is a defect in a transport protein 144 00:06:53,850 --> 00:06:56,320 that carries oxygen around the body. 145 00:06:56,320 --> 00:06:59,010 So we're going to talk about hemoglobin. 146 00:06:59,010 --> 00:07:00,780 These diseases are what are known 147 00:07:00,780 --> 00:07:04,860 as inborn errors of metabolism, or that's 148 00:07:04,860 --> 00:07:06,330 kind of a complex term. 149 00:07:06,330 --> 00:07:09,750 Or genetically linked diseases, because there 150 00:07:09,750 --> 00:07:13,500 is a single defect in a DNA strand 151 00:07:13,500 --> 00:07:17,620 that then gets transcribed into an RNA strand. 152 00:07:17,620 --> 00:07:22,800 So one base defect that then becomes an amino acid defect 153 00:07:22,800 --> 00:07:24,600 in your protein strand. 154 00:07:24,600 --> 00:07:28,050 So these are tiny changes in the protein that 155 00:07:28,050 --> 00:07:31,500 cause dramatic changes in the structure 156 00:07:31,500 --> 00:07:33,520 and function of the protein. 157 00:07:33,520 --> 00:07:35,430 And what you will see with hemoglobin 158 00:07:35,430 --> 00:07:40,630 is it causes a real problem with the quaternary structure 159 00:07:40,630 --> 00:07:43,530 and causes proteins to aggregate. 160 00:07:43,530 --> 00:07:54,620 So hemoglobin is the dominant protein in red blood cells. 161 00:08:02,480 --> 00:08:04,040 Or erythrocytes. 162 00:08:04,040 --> 00:08:08,600 And in fact, the differentiation of the red blood cell 163 00:08:08,600 --> 00:08:10,820 as it comes from progenitor cells 164 00:08:10,820 --> 00:08:14,360 goes through a process where the red blood cell dumps out 165 00:08:14,360 --> 00:08:17,570 its nucleus so it can't divide anymore. 166 00:08:17,570 --> 00:08:20,120 And basically, the content of the cell 167 00:08:20,120 --> 00:08:22,910 is extremely high in hemoglobin. 168 00:08:22,910 --> 00:08:25,640 You've packed the hemoglobin into the red blood 169 00:08:25,640 --> 00:08:28,590 cell at the cost of losing the nucleus. 170 00:08:28,590 --> 00:08:30,740 So that's terminally differentiated. 171 00:08:30,740 --> 00:08:32,720 Can't become a red blood cell. 172 00:08:32,720 --> 00:08:34,669 It can't divide anymore. 173 00:08:34,669 --> 00:08:36,620 And it has about a half-life, they 174 00:08:36,620 --> 00:08:42,230 have about a half-life of 100 days. 175 00:08:42,230 --> 00:08:44,630 So they turn over, and then that's it. 176 00:08:44,630 --> 00:08:46,970 And when red blood cells turn over, 177 00:08:46,970 --> 00:08:49,880 the hemoglobin has to be taken care of in order 178 00:08:49,880 --> 00:08:51,440 that it's not toxic. 179 00:08:51,440 --> 00:08:55,580 Red blood cells are red because of a particular molecule 180 00:08:55,580 --> 00:09:01,920 that's in the hemoglobin called the heme molecule, which 181 00:09:01,920 --> 00:09:06,810 is bound to iron, which provides the hemoglobin 182 00:09:06,810 --> 00:09:11,180 with the capacity to pick up oxygen in your lungs, 183 00:09:11,180 --> 00:09:14,100 travel it around the body, and then leave it 184 00:09:14,100 --> 00:09:15,150 where it's needed. 185 00:09:15,150 --> 00:09:18,420 And then replace the oxygen with CO2 186 00:09:18,420 --> 00:09:21,300 and take the CO2 back to the lungs in order 187 00:09:21,300 --> 00:09:22,910 for you to respire it out. 188 00:09:22,910 --> 00:09:23,660 OK? 189 00:09:23,660 --> 00:09:34,770 So hemoglobin carries oxygen and CO2, 190 00:09:34,770 --> 00:09:39,030 from oxygen from the lungs, CO2 back to the lungs. 191 00:09:39,030 --> 00:09:42,480 And the reason why you need the iron 192 00:09:42,480 --> 00:09:47,050 is that the iron is coordinated to the oxygen. 193 00:09:47,050 --> 00:09:48,060 So the heme molecule-- 194 00:09:48,060 --> 00:09:49,230 I won't draw it. 195 00:09:49,230 --> 00:09:52,800 If you want to see it, it's a big, complex organic structure. 196 00:09:52,800 --> 00:09:54,480 Very interesting structure. 197 00:09:54,480 --> 00:09:56,880 But something for another day here. 198 00:09:56,880 --> 00:09:59,910 But I want to just stress to you that the iron heme 199 00:09:59,910 --> 00:10:01,350 complex is red. 200 00:10:01,350 --> 00:10:03,180 That's why your blood cells are red. 201 00:10:03,180 --> 00:10:04,880 Your blood cells don't have a nucleus 202 00:10:04,880 --> 00:10:06,990 so they can cram in lots more hemoglobin. 203 00:10:06,990 --> 00:10:09,510 So it's kind of a fascinating situation. 204 00:10:09,510 --> 00:10:15,600 So hemoglobin is an example of a homotetrameric protein. 205 00:10:15,600 --> 00:10:17,360 And it has four subunits. 206 00:10:21,730 --> 00:10:24,620 Two of one flavor and two of another. 207 00:10:24,620 --> 00:10:29,800 So we call this an alpha 2 beta 2 protein, 208 00:10:29,800 --> 00:10:32,390 differentiating the alpha subunits and the beta ones. 209 00:10:32,390 --> 00:10:32,890 Yes. 210 00:10:32,890 --> 00:10:34,740 AUDIENCE: Why isn't it homotetrameric? 211 00:10:34,740 --> 00:10:36,510 PROFESSOR: Why isn't it homotetrameric? 212 00:10:36,510 --> 00:10:38,482 AUDIENCE: [INAUDIBLE] 213 00:10:38,482 --> 00:10:39,940 PROFESSOR: You could ask why is it? 214 00:10:39,940 --> 00:10:40,700 I don't know. 215 00:10:40,700 --> 00:10:42,670 I mean, there will be interactions 216 00:10:42,670 --> 00:10:47,080 amongst the subunits that favor that particular packaging. 217 00:10:47,080 --> 00:10:49,550 The subunits are kind of similar in shape. 218 00:10:49,550 --> 00:10:51,790 They have what's called a globin fold. 219 00:10:51,790 --> 00:10:54,910 You can more or less pick out those tubes, remember, 220 00:10:54,910 --> 00:10:56,980 alpha helices. 221 00:10:56,980 --> 00:11:00,560 They could form tetramers that are all the same, 222 00:11:00,560 --> 00:11:04,660 but the energetically favored form is the two and two. 223 00:11:04,660 --> 00:11:07,370 Hemoglobin is a tetrameric protein, 224 00:11:07,370 --> 00:11:10,660 because that's really advantageous for picking up 225 00:11:10,660 --> 00:11:15,710 oxygen and dropping off oxygen in a very narrow oxygen range. 226 00:11:15,710 --> 00:11:17,710 So there are proteins called globins 227 00:11:17,710 --> 00:11:21,700 that just one of these that can bind oxygen. 228 00:11:21,700 --> 00:11:24,160 Hemoglobin is tetrameric because it has 229 00:11:24,160 --> 00:11:26,180 a cooperative oxygen binding. 230 00:11:26,180 --> 00:11:28,770 So in a very narrow range of oxygen, 231 00:11:28,770 --> 00:11:32,410 it fills all four sites in the tetrameric protein 232 00:11:32,410 --> 00:11:34,130 with an oxygen Molecule. 233 00:11:34,130 --> 00:11:38,080 So it's very advantageous from a physics perspective 234 00:11:38,080 --> 00:11:40,827 that it responds to very narrow changes 235 00:11:40,827 --> 00:11:42,660 in oxygen. Does that make sense to everyone? 236 00:11:42,660 --> 00:11:43,303 Yeah. 237 00:11:43,303 --> 00:11:45,670 AUDIENCE: [INAUDIBLE] 238 00:11:45,670 --> 00:11:46,690 PROFESSOR: OK. 239 00:11:46,690 --> 00:11:50,140 It means, anything that's cooperative means that one, 240 00:11:50,140 --> 00:11:53,290 let's say I've got a tetramer of hemoglobin. 241 00:11:53,290 --> 00:11:57,220 One oxygen binds to one of them. 242 00:11:57,220 --> 00:11:58,930 So I'm a binding oxygen here. 243 00:11:58,930 --> 00:12:01,330 And then binding to the next, the next, and the next 244 00:12:01,330 --> 00:12:02,960 gets easier and easier. 245 00:12:02,960 --> 00:12:05,800 So they sort of want to come in as a team. 246 00:12:05,800 --> 00:12:09,340 And that's handy for maximizing oxygen transport 247 00:12:09,340 --> 00:12:13,120 around the body in a narrow oxygen range, which we can only 248 00:12:13,120 --> 00:12:15,050 deal with what's out there in the atmosphere, 249 00:12:15,050 --> 00:12:16,990 so we have to make this work. 250 00:12:16,990 --> 00:12:18,460 Does that answer your question? 251 00:12:18,460 --> 00:12:19,190 OK. 252 00:12:19,190 --> 00:12:19,690 All right. 253 00:12:19,690 --> 00:12:20,380 So where was I? 254 00:12:20,380 --> 00:12:21,790 OK. 255 00:12:21,790 --> 00:12:23,320 So what we're going to do today. 256 00:12:23,320 --> 00:12:25,210 We're going to look at hemoglobin. 257 00:12:25,210 --> 00:12:26,090 It's the tetramer. 258 00:12:26,090 --> 00:12:30,010 Those discoid structures are the hemes that I just mentioned. 259 00:12:30,010 --> 00:12:32,590 I've drawn them as this sort of four-leafed clover 260 00:12:32,590 --> 00:12:34,870 here just for simplicity. 261 00:12:34,870 --> 00:12:38,500 And there is a single defect in the sequence 262 00:12:38,500 --> 00:12:42,730 of the single monomer subunits in hemoglobin. 263 00:12:42,730 --> 00:12:45,910 So each of these-- 264 00:12:45,910 --> 00:12:46,970 let's go here. 265 00:12:56,150 --> 00:12:59,840 So there are four proteins-- beta globin, 266 00:12:59,840 --> 00:13:04,940 two copies of beta globin, and two copies of alpha globin. 267 00:13:04,940 --> 00:13:06,080 They are all-- let me see. 268 00:13:06,080 --> 00:13:07,250 What's the size? 269 00:13:07,250 --> 00:13:09,010 Do, do, do, do. 270 00:13:09,010 --> 00:13:12,527 [INAUDIBLE] You know, I can never see things 271 00:13:12,527 --> 00:13:13,610 when I'm up at the screen. 272 00:13:13,610 --> 00:13:19,540 But they're about 150. 273 00:13:19,540 --> 00:13:22,640 156. 274 00:13:22,640 --> 00:13:23,140 OK. 275 00:13:23,140 --> 00:13:28,450 So they're about 146 amino acids long in each of them. 276 00:13:28,450 --> 00:13:31,400 And a single defect in the beta globin 277 00:13:31,400 --> 00:13:35,200 where you have a change from glutamic acid 278 00:13:35,200 --> 00:13:41,550 residue 6 to valine at residues 6-- 279 00:13:41,550 --> 00:13:45,370 one change in beta globin, which means 280 00:13:45,370 --> 00:13:47,050 two changes in the whole structure, 281 00:13:47,050 --> 00:13:49,600 because there are two beta globins-- 282 00:13:49,600 --> 00:13:52,600 alters the properties of the hemoglobin and causes 283 00:13:52,600 --> 00:13:55,357 what's called sickling of your red blood cells. 284 00:13:55,357 --> 00:13:57,190 So let's take a look at what that would look 285 00:13:57,190 --> 00:14:01,780 like at the amino acid level. 286 00:14:01,780 --> 00:14:05,920 Glutamic acid is one of your charged amino acids. 287 00:14:05,920 --> 00:14:08,380 I'm just going to draw a little bit of it 288 00:14:08,380 --> 00:14:09,460 as it were in a peptide. 289 00:14:15,270 --> 00:14:18,130 And it's at position 6 in the sequence. 290 00:14:18,130 --> 00:14:21,210 So it's six residues from the amino terminus 291 00:14:21,210 --> 00:14:23,940 because we always write things in this direction. 292 00:14:23,940 --> 00:14:34,420 And the change takes place to put in place a valine. 293 00:14:37,020 --> 00:14:41,670 And there's a pretty big change in identity and personality 294 00:14:41,670 --> 00:14:43,020 of those residues. 295 00:14:43,020 --> 00:14:47,190 You've gone from polar charged, to neutral, big, fluffy, 296 00:14:47,190 --> 00:14:49,050 hydrophobic residue. 297 00:14:49,050 --> 00:14:50,590 And it's really amazing. 298 00:14:50,590 --> 00:14:55,290 So the beta globin is expressed on chromosome 11. 299 00:14:55,290 --> 00:14:59,220 It's 134 million base pairs. 300 00:14:59,220 --> 00:15:01,720 One base has changed. 301 00:15:01,720 --> 00:15:06,560 So what you have in the DNA, in the normal DNA that 302 00:15:06,560 --> 00:15:09,650 encodes the normal beta globin gene, 303 00:15:09,650 --> 00:15:13,040 there's a particular sequence of nucleic acids. 304 00:15:13,040 --> 00:15:15,260 This is what the double strand would look like. 305 00:15:15,260 --> 00:15:18,440 We're going to see way more about nucleic acids next week. 306 00:15:18,440 --> 00:15:21,490 When that gets converted to the messenger RNA, 307 00:15:21,490 --> 00:15:25,460 you get a particular code that in the genetic code 308 00:15:25,460 --> 00:15:27,170 codes for glutamate acids. 309 00:15:27,170 --> 00:15:28,400 Everything's normal. 310 00:15:28,400 --> 00:15:33,380 A single change, if we change the center nucleic acid 311 00:15:33,380 --> 00:15:38,450 within the DNA, it makes a different messenger RNA. 312 00:15:38,450 --> 00:15:43,820 And one base pair puts in valine instead of glutamic acid out 313 00:15:43,820 --> 00:15:46,920 of 134 million base pairs. 314 00:15:46,920 --> 00:15:51,590 So what happens in the normal hemoglobin, 315 00:15:51,590 --> 00:15:52,970 you have normal behavior. 316 00:15:52,970 --> 00:15:56,130 You had this tetrameric structure. 317 00:15:56,130 --> 00:15:59,000 It cooperatively carries oxygen. It moves 318 00:15:59,000 --> 00:16:00,710 around the blood no problem. 319 00:16:00,710 --> 00:16:03,560 Excuse me, it sits in the erythrocytes 320 00:16:03,560 --> 00:16:05,600 or red blood cells no problem. 321 00:16:05,600 --> 00:16:07,640 The minute you have that mutation, 322 00:16:07,640 --> 00:16:10,310 the hemoglobin molecules start to associate 323 00:16:10,310 --> 00:16:13,280 into clusters like fibrillar clusters, 324 00:16:13,280 --> 00:16:16,730 because each tetramer gets glued to another tetramer, 325 00:16:16,730 --> 00:16:18,470 and another one, and another one. 326 00:16:18,470 --> 00:16:21,080 So you have hemoglobin not behaving 327 00:16:21,080 --> 00:16:24,230 as this beautiful, independent quaternary structure, 328 00:16:24,230 --> 00:16:27,260 but rather sticking to, physically 329 00:16:27,260 --> 00:16:29,210 sticking to other Molecules 330 00:16:29,210 --> 00:16:31,190 And those tangles get, those molecules 331 00:16:31,190 --> 00:16:35,090 get so large that they start to form 332 00:16:35,090 --> 00:16:37,820 long and inflexible chains. 333 00:16:37,820 --> 00:16:41,530 And it's such a dramatic change that that discoid structure 334 00:16:41,530 --> 00:16:43,970 that you're familiar with for red blood cells 335 00:16:43,970 --> 00:16:46,430 suddenly becomes a sickle shape. 336 00:16:46,430 --> 00:16:49,520 So that would be the normal cell with normal hemoglobin. 337 00:16:49,520 --> 00:16:52,040 But sickle cell, they look like this. 338 00:16:52,040 --> 00:16:55,310 They're kind of curved, odd, a very odd shape. 339 00:16:55,310 --> 00:16:57,570 And the problem is red blood cells 340 00:16:57,570 --> 00:16:59,600 have evolved to move really smoothly 341 00:16:59,600 --> 00:17:01,290 through your capillaries. 342 00:17:01,290 --> 00:17:03,920 As soon as you get a different shape that's 343 00:17:03,920 --> 00:17:08,150 sort of not that discoid structure, 344 00:17:08,150 --> 00:17:11,450 they start clogging in the capillaries. 345 00:17:11,450 --> 00:17:15,319 And when you have the defect where all of your hemoglobin 346 00:17:15,319 --> 00:17:17,599 is messed up with this variation, 347 00:17:17,599 --> 00:17:21,260 it's incredibly painful, because think of all your capillaries 348 00:17:21,260 --> 00:17:24,069 going out to the farther reaches of your joints. 349 00:17:24,069 --> 00:17:28,790 Those very thin blood vessels are blocked up 350 00:17:28,790 --> 00:17:32,180 with the sickle red blood cells that are caused 351 00:17:32,180 --> 00:17:34,550 by the variation in hemoglobin. 352 00:17:34,550 --> 00:17:38,240 So that one little defect takes us all the way 353 00:17:38,240 --> 00:17:39,710 to a serious disease. 354 00:17:39,710 --> 00:17:40,250 All right? 355 00:17:40,250 --> 00:17:42,140 So what I want to do very briefly 356 00:17:42,140 --> 00:17:45,500 is show you the molecular basis for this. 357 00:17:45,500 --> 00:17:46,900 All right. 358 00:17:46,900 --> 00:17:51,230 And the defect actually appears on the two beta globin chains, 359 00:17:51,230 --> 00:17:53,270 but right on the outside of the protein, 360 00:17:53,270 --> 00:17:55,000 not in the middle of the protein. 361 00:17:55,000 --> 00:17:58,670 Because this is a defect that affects how proteins interact 362 00:17:58,670 --> 00:18:00,860 with other proteins, not the function 363 00:18:00,860 --> 00:18:02,300 of the protein on its own. 364 00:18:02,300 --> 00:18:05,480 Probably still carries oxygen just fine. 365 00:18:05,480 --> 00:18:08,750 But it's the mechanical change in the hemoglobin 366 00:18:08,750 --> 00:18:11,360 that causes the disease. 367 00:18:11,360 --> 00:18:12,270 OK. 368 00:18:12,270 --> 00:18:15,650 So sickle cell anemia, the hemoglobin 369 00:18:15,650 --> 00:18:18,440 is now called hemoglobin S with that mutation 370 00:18:18,440 --> 00:18:20,360 that I just described. 371 00:18:20,360 --> 00:18:23,570 And when people are heterozygous, 372 00:18:23,570 --> 00:18:26,870 it means they have one good copy of the gene that's normal 373 00:18:26,870 --> 00:18:28,910 and the copy of the gene that's the variant. 374 00:18:28,910 --> 00:18:31,820 And you'll learn much more about this in human genetics 375 00:18:31,820 --> 00:18:33,870 when we talk about that later on. 376 00:18:33,870 --> 00:18:39,440 So you have a mixture of the OK hemoglobin and the sickle cell 377 00:18:39,440 --> 00:18:40,460 hemoglobin. 378 00:18:40,460 --> 00:18:43,910 People who are homozygous for the defect, all 379 00:18:43,910 --> 00:18:47,900 of their hemoglobin is disrupted, 380 00:18:47,900 --> 00:18:49,730 and those are the people who really end up 381 00:18:49,730 --> 00:18:52,700 in hospital with a lot of transfusions, and so on. 382 00:18:52,700 --> 00:18:55,850 The heterozygous, actually, you can manage quite well with. 383 00:18:55,850 --> 00:18:57,800 And I'm going to show you in a minute that 384 00:18:57,800 --> 00:19:01,280 in some parts of the world, being heterozygous-- 385 00:19:01,280 --> 00:19:04,730 i.e., having some of your hemoglobin with a defect 386 00:19:04,730 --> 00:19:06,050 and some without it-- 387 00:19:06,050 --> 00:19:08,610 actually confers an advantage. 388 00:19:08,610 --> 00:19:11,010 It's a really cool story. 389 00:19:11,010 --> 00:19:15,500 So what I'm going to do is quickly show you 390 00:19:15,500 --> 00:19:17,540 the wire structure. 391 00:19:17,540 --> 00:19:23,510 OK, so this is the structure that elucidated the real reason 392 00:19:23,510 --> 00:19:26,510 for the interaction. 393 00:19:26,510 --> 00:19:30,200 What happens when you have this mutation. 394 00:19:30,200 --> 00:19:32,210 And it was a structure that was captured 395 00:19:32,210 --> 00:19:34,535 of a dimer of hemoglobin molecules 396 00:19:34,535 --> 00:19:36,410 where you could really see what was happening 397 00:19:36,410 --> 00:19:40,070 at the interface and the sorts of changes that had been put 398 00:19:40,070 --> 00:19:42,890 in place by that variation from the charged 399 00:19:42,890 --> 00:19:44,490 to the neutral structure. 400 00:19:44,490 --> 00:19:46,790 So for any of you who want to pop by, 401 00:19:46,790 --> 00:19:50,240 I can start to show you how to manipulate PyMOL. 402 00:19:50,240 --> 00:19:52,370 We can do that separately from class. 403 00:19:52,370 --> 00:19:55,670 But this is a dimer of tetramers. 404 00:19:55,670 --> 00:20:01,220 And if I just show you just some of the subunits, 405 00:20:01,220 --> 00:20:07,700 I can actually show you how there's 406 00:20:07,700 --> 00:20:10,100 two of each subunit in each structure. 407 00:20:10,100 --> 00:20:13,400 So if I, go I can pick some out. 408 00:20:13,400 --> 00:20:15,380 Every other one. 409 00:20:15,380 --> 00:20:18,200 And then I can color them a different color. 410 00:20:18,200 --> 00:20:21,710 You can see where the globins, where the beta globin are 411 00:20:21,710 --> 00:20:23,390 and where the alpha globins are. 412 00:20:23,390 --> 00:20:25,110 That's still looks like chicken wire. 413 00:20:25,110 --> 00:20:27,000 It's very unsatisfactory. 414 00:20:27,000 --> 00:20:31,130 So what I can do is I can show you everything as a cartoon 415 00:20:31,130 --> 00:20:33,890 and get rid of all those little lines. 416 00:20:33,890 --> 00:20:37,700 And then you can see perfectly the structure 417 00:20:37,700 --> 00:20:41,720 where you see two beta globins and two alpha globins 418 00:20:41,720 --> 00:20:42,690 in each structure. 419 00:20:42,690 --> 00:20:43,190 OK? 420 00:20:43,190 --> 00:20:45,530 So what we're going to do next is zoom in 421 00:20:45,530 --> 00:20:47,840 to see what's happening where we've 422 00:20:47,840 --> 00:20:51,140 done this mutation, what's going on with the placement 423 00:20:51,140 --> 00:20:52,670 of the valine in that structure. 424 00:20:52,670 --> 00:20:53,170 All right? 425 00:20:59,800 --> 00:21:05,290 And wherever I put a four-letter code-- so that one was 2HBS-- 426 00:21:05,290 --> 00:21:08,200 that's what's known as the protein data bank code, 427 00:21:08,200 --> 00:21:11,530 and it enables you to go fetch the coordinates 428 00:21:11,530 --> 00:21:12,470 of that protein. 429 00:21:12,470 --> 00:21:14,380 So if any of you for the late project 430 00:21:14,380 --> 00:21:17,510 want to do a protein structure and print it, come to me 431 00:21:17,510 --> 00:21:19,210 and I'll explain a lot more about that. 432 00:21:19,210 --> 00:21:21,260 Or the TAs can also do that. 433 00:21:21,260 --> 00:21:25,750 So let me now move you to looking in closely 434 00:21:25,750 --> 00:21:26,800 to the variations. 435 00:21:26,800 --> 00:21:29,710 So what I've done here is I've actually colored-- 436 00:21:29,710 --> 00:21:32,800 the beta globin is purple, and the alpha globin 437 00:21:32,800 --> 00:21:34,660 is cyan colored. 438 00:21:34,660 --> 00:21:37,120 You can see the hemes in each of the subunits. 439 00:21:37,120 --> 00:21:39,640 Those are those red wire things. 440 00:21:39,640 --> 00:21:42,580 And now we've zoomed into the place where 441 00:21:42,580 --> 00:21:46,240 the mutation is where you have a valine instead 442 00:21:46,240 --> 00:21:48,160 of carboxylic acid. 443 00:21:48,160 --> 00:21:51,970 And what you can see from this image which should stop 444 00:21:51,970 --> 00:21:56,770 is that the valine on one subunit in one homotetramer 445 00:21:56,770 --> 00:22:01,030 interacts with a sticky patch on another subunit that's 446 00:22:01,030 --> 00:22:05,110 made up of phenylalanine 85 in the adjacent protein 447 00:22:05,110 --> 00:22:08,300 and leucine 88 in the adjacent protein. 448 00:22:08,300 --> 00:22:11,860 So this sticky patch on one surface glues 449 00:22:11,860 --> 00:22:16,820 onto a sticky patch on the surface of another tetramer. 450 00:22:16,820 --> 00:22:20,830 If you had glutamic glutamate there, would that form? 451 00:22:20,830 --> 00:22:21,400 No. 452 00:22:21,400 --> 00:22:23,980 In fact, it would be quite deterred from forming 453 00:22:23,980 --> 00:22:27,430 because you don't want to cram that negatively charged element 454 00:22:27,430 --> 00:22:30,070 into those two hydrophobic residues. 455 00:22:30,070 --> 00:22:34,480 So what you've gone from is a situation where this really 456 00:22:34,480 --> 00:22:35,770 is fine on the surface. 457 00:22:35,770 --> 00:22:36,610 It's hydrated. 458 00:22:36,610 --> 00:22:38,350 It's not sticking to anything. 459 00:22:38,350 --> 00:22:51,440 To another situation where you have phenylalanine and leucine, 460 00:22:51,440 --> 00:22:56,360 which are both hydrophobic, providing a patch on the one 461 00:22:56,360 --> 00:23:01,130 tetramer where the valine from the other tetramer combined. 462 00:23:01,130 --> 00:23:03,440 And because the molecule's a tetramer, 463 00:23:03,440 --> 00:23:06,800 on each of the subunits, there is also 464 00:23:06,800 --> 00:23:10,310 another valine that will go off and do that elsewhere, 465 00:23:10,310 --> 00:23:11,690 and another valine. 466 00:23:11,690 --> 00:23:14,270 And there's one you can't see that's tucked behind. 467 00:23:14,270 --> 00:23:18,500 So that's why the hemoglobin forms these structures, 468 00:23:18,500 --> 00:23:21,260 because every hemoglobin molecule has 469 00:23:21,260 --> 00:23:25,440 two places to stick to another hemoglobin tetramer, and so on. 470 00:23:25,440 --> 00:23:29,420 So think of the repercussions from one nucleic acid change 471 00:23:29,420 --> 00:23:31,490 that's really quite remarkable. 472 00:23:31,490 --> 00:23:35,720 So what we've seen here is that that change occurs. 473 00:23:35,720 --> 00:23:38,880 And just a couple of moments for you to think about this, 474 00:23:38,880 --> 00:23:41,870 you can have variations at that site that 475 00:23:41,870 --> 00:23:43,160 won't cause a problem. 476 00:23:43,160 --> 00:23:45,200 Which ones of these do you think are 477 00:23:45,200 --> 00:23:51,140 least likely to cause a sickle cell type of phenomenon? 478 00:23:51,140 --> 00:23:55,330 So tyrosine, serine, aspartic acid, and lysine? 479 00:23:55,330 --> 00:23:57,990 So I'm going to change the glutamate to something else. 480 00:23:57,990 --> 00:24:00,450 Which one's going to have a perfectly normal hemoglobin? 481 00:24:00,450 --> 00:24:01,720 There's one that stands out. 482 00:24:01,720 --> 00:24:02,220 Yeah. 483 00:24:02,220 --> 00:24:02,700 AUDIENCE: [INAUDIBLE] 484 00:24:02,700 --> 00:24:03,533 PROFESSOR: Aspartic. 485 00:24:03,533 --> 00:24:04,040 That's fine. 486 00:24:04,040 --> 00:24:04,640 No problem. 487 00:24:04,640 --> 00:24:06,890 It just switched it for its younger brother. 488 00:24:06,890 --> 00:24:09,010 Well, which one of the others? 489 00:24:09,010 --> 00:24:10,760 And in many cases here, you could probably 490 00:24:10,760 --> 00:24:12,920 argue your way to all of them. 491 00:24:12,920 --> 00:24:14,480 But one would be pretty bad. 492 00:24:14,480 --> 00:24:18,260 Which one would be pretty bad? 493 00:24:18,260 --> 00:24:19,330 Tyrosine, exactly. 494 00:24:19,330 --> 00:24:20,060 It's another. 495 00:24:20,060 --> 00:24:21,650 Even though it's got that OH group, 496 00:24:21,650 --> 00:24:23,960 it's still pretty hydrophobic because 497 00:24:23,960 --> 00:24:26,480 of that ring system there. 498 00:24:26,480 --> 00:24:28,760 What about the other two, serine and lysine? 499 00:24:28,760 --> 00:24:29,970 What do you think? 500 00:24:29,970 --> 00:24:33,080 Which one would probably be, in fact, the least detrimental 501 00:24:33,080 --> 00:24:35,860 of those remaining two? 502 00:24:35,860 --> 00:24:39,120 And give me the reason as well. 503 00:24:39,120 --> 00:24:39,840 Yes. 504 00:24:39,840 --> 00:24:40,560 AUDIENCE: Lysine. 505 00:24:40,560 --> 00:24:41,760 PROFESSOR: Lysine. 506 00:24:41,760 --> 00:24:43,950 I think it would be lysine because lysine is now 507 00:24:43,950 --> 00:24:45,390 positively charged. 508 00:24:45,390 --> 00:24:50,070 It's equally unlikely to want to do this goofy interaction 509 00:24:50,070 --> 00:24:53,310 because it is also charged, just charged in the other direction. 510 00:24:53,310 --> 00:24:56,820 But one could also argue that serine would be OK 511 00:24:56,820 --> 00:25:00,720 because it's a little bit more polar, so it 512 00:25:00,720 --> 00:25:02,820 wouldn't cause as much problem. 513 00:25:02,820 --> 00:25:03,680 OK. 514 00:25:03,680 --> 00:25:06,810 Finally, this issue with sickle cell anemia, 515 00:25:06,810 --> 00:25:09,300 there's some fascinating data that 516 00:25:09,300 --> 00:25:11,350 shows in parts of the world-- 517 00:25:11,350 --> 00:25:15,870 for example, during a drug trial for plasmodium falciparum, one 518 00:25:15,870 --> 00:25:18,970 of the causative agents of malaria, 519 00:25:18,970 --> 00:25:22,440 they found that 1 out of 15 people with the sickle cell 520 00:25:22,440 --> 00:25:27,000 trait was infected with malaria, whereas then the people who 521 00:25:27,000 --> 00:25:31,650 were healthy, normal homozygotes for the right hemoglobin, 522 00:25:31,650 --> 00:25:36,720 14 out of 15 were infected with plasmodium falciparum. 523 00:25:36,720 --> 00:25:39,700 Now why do you think that is? 524 00:25:39,700 --> 00:25:44,633 How can we relate the infectivity of a parasite 525 00:25:44,633 --> 00:25:45,675 with the shape of a cell? 526 00:25:51,540 --> 00:25:53,760 We've gone from these juicy-looking red blood 527 00:25:53,760 --> 00:25:57,210 cells, nice and round and probably quite open, 528 00:25:57,210 --> 00:26:00,000 to a cell that's sort of difficult to shape. 529 00:26:00,000 --> 00:26:02,220 So it turns out that the parasite 530 00:26:02,220 --> 00:26:07,230 doesn't want to infect the sickle cell red blood 531 00:26:07,230 --> 00:26:09,630 cells anywhere near as well. 532 00:26:09,630 --> 00:26:13,740 And there are, for example, other bloods tested which 533 00:26:13,740 --> 00:26:15,480 shows the same correlation. 534 00:26:15,480 --> 00:26:19,560 And here's a map of Africa where you see a massive overlap 535 00:26:19,560 --> 00:26:22,930 of the prevalence of the sickle cell trait 536 00:26:22,930 --> 00:26:26,860 and the presence of plasmodium falciparum. 537 00:26:26,860 --> 00:26:30,900 So there is an evolutionary advantage 538 00:26:30,900 --> 00:26:34,980 to having the heterozygous variant 539 00:26:34,980 --> 00:26:38,010 where you have some normal hemoglobin but some 540 00:26:38,010 --> 00:26:40,620 of the sickling hemoglobin, because it confers 541 00:26:40,620 --> 00:26:46,020 you some resistance to malaria. 542 00:26:46,020 --> 00:26:49,260 It's not good to have both of them, 543 00:26:49,260 --> 00:26:50,910 the variant that causes sickling, 544 00:26:50,910 --> 00:26:52,980 because that's painful and it really 545 00:26:52,980 --> 00:26:54,960 causes a lot of health disorders. 546 00:26:54,960 --> 00:26:58,860 It's just when you have one of each gene encoding 547 00:26:58,860 --> 00:27:00,060 both variants. 548 00:27:00,060 --> 00:27:02,430 OK? 549 00:27:02,430 --> 00:27:02,930 All right. 550 00:27:02,930 --> 00:27:03,600 Great. 551 00:27:03,600 --> 00:27:04,100 OK. 552 00:27:04,100 --> 00:27:06,590 So now we're going to talk about enzymes. 553 00:27:06,590 --> 00:27:11,810 And these are the proteins that catalyze reactions. 554 00:27:16,030 --> 00:27:18,500 Any questions about that? 555 00:27:18,500 --> 00:27:20,960 So while a lot of disease states actually 556 00:27:20,960 --> 00:27:23,420 might be bred out because someone 557 00:27:23,420 --> 00:27:27,140 would be at a disadvantage with a particular disease, 558 00:27:27,140 --> 00:27:30,440 in this case, that trait has been maintained 559 00:27:30,440 --> 00:27:32,905 because it offers a very different advantage 560 00:27:32,905 --> 00:27:33,905 with respect to disease. 561 00:27:39,150 --> 00:27:39,830 OK. 562 00:27:39,830 --> 00:27:43,500 Let's talk about enzymes for a moment. 563 00:27:43,500 --> 00:27:45,500 Or for the rest of the class, in fact. 564 00:27:45,500 --> 00:27:46,160 OK. 565 00:27:46,160 --> 00:27:50,810 So enzymes are the heavy lifters of the protein world 566 00:27:50,810 --> 00:27:55,280 because they catalyze all the reactions in metabolism, 567 00:27:55,280 --> 00:27:58,640 in biosynthesis, all kinds of transformations 568 00:27:58,640 --> 00:28:00,440 that make you want you are. 569 00:28:00,440 --> 00:28:02,630 Enzyme is a protein-based catalyst. 570 00:28:02,630 --> 00:28:03,500 You all know that. 571 00:28:12,260 --> 00:28:13,580 Terrible writing again. 572 00:28:13,580 --> 00:28:15,500 There were a couple of other times 573 00:28:15,500 --> 00:28:17,630 I just quickly want to give you. 574 00:28:17,630 --> 00:28:21,380 So an enzyme, there is also a term known as an isozyme. 575 00:28:24,250 --> 00:28:26,860 And an allozyme. 576 00:28:26,860 --> 00:28:27,730 You may see them. 577 00:28:27,730 --> 00:28:29,710 You'll see allozyme less commonly, 578 00:28:29,710 --> 00:28:32,890 but you'll see isozyme quite commonly. 579 00:28:32,890 --> 00:28:36,130 An isozyme of one enzyme is a variation 580 00:28:36,130 --> 00:28:38,980 on the enzyme that catalyzes the same reaction, 581 00:28:38,980 --> 00:28:40,810 but it's expressed on a different gene. 582 00:28:52,470 --> 00:28:57,150 An allozyme is the same enzyme, but with a variation in it. 583 00:28:57,150 --> 00:29:02,060 So it's encoded by an allele of one gene. 584 00:29:02,060 --> 00:29:06,540 So it's just a variation of the gene that might have 585 00:29:06,540 --> 00:29:08,250 happened through a mutation. 586 00:29:08,250 --> 00:29:12,030 Still catalyzes the reaction, but there's a slight change 587 00:29:12,030 --> 00:29:13,080 in the sequence. 588 00:29:13,080 --> 00:29:15,720 But they're coded by the same gene. 589 00:29:15,720 --> 00:29:18,950 Same gene, with a variation. 590 00:29:22,010 --> 00:29:26,110 And as I said, you will see the isozyme term more commonly 591 00:29:26,110 --> 00:29:28,480 than the allozyme term. 592 00:29:28,480 --> 00:29:30,490 Now why do we need enzymes? 593 00:29:30,490 --> 00:29:36,080 Well, the problem is there are physiologic reactions 594 00:29:36,080 --> 00:29:39,050 that we need to carry out that are just 595 00:29:39,050 --> 00:29:44,300 too hard to carry out at room temperature pH 7 in water. 596 00:29:44,300 --> 00:29:45,870 They just don't occur. 597 00:29:45,870 --> 00:29:58,300 So you need enzyme catalysis for all 598 00:29:58,300 --> 00:29:59,740 of your metabolic reactions. 599 00:29:59,740 --> 00:30:02,410 Let me just give you one trivial example. 600 00:30:02,410 --> 00:30:09,040 This bond you already know nicely now. 601 00:30:09,040 --> 00:30:11,350 Peptide or amide bond. 602 00:30:11,350 --> 00:30:13,720 If I want to hydrolyze that, if I 603 00:30:13,720 --> 00:30:19,130 want to break it open, pH 7, physiologic temperature, so 604 00:30:19,130 --> 00:30:24,370 37c, in water, it would take me-- 605 00:30:24,370 --> 00:30:25,270 how many years is it? 606 00:30:25,270 --> 00:30:29,710 The half-life of that bond would be 600 years. 607 00:30:29,710 --> 00:30:30,210 OK? 608 00:30:35,960 --> 00:30:38,050 That's pretty untenable for digesting a Big 609 00:30:38,050 --> 00:30:41,260 Mac even that even under the best of circumstances. 610 00:30:41,260 --> 00:30:46,150 So we need enzymes to speed up breaking down proteins 611 00:30:46,150 --> 00:30:48,550 and carrying out reactions because otherwise, 612 00:30:48,550 --> 00:30:50,860 we just can't-- we can't do anything. 613 00:30:50,860 --> 00:30:52,640 So what I want to describe to you 614 00:30:52,640 --> 00:30:55,510 are some of the details of how enzymes work 615 00:30:55,510 --> 00:30:58,850 and then how we can control the function of enzymes. 616 00:30:58,850 --> 00:31:05,715 So typical enzymes take a substrate to a product. 617 00:31:09,330 --> 00:31:14,050 Some enzymes may take two substrates 618 00:31:14,050 --> 00:31:15,130 and make one product. 619 00:31:15,130 --> 00:31:17,350 Some enzymes maybe take one substrate 620 00:31:17,350 --> 00:31:18,820 and make two products. 621 00:31:18,820 --> 00:31:20,500 It just depends on the transformation 622 00:31:20,500 --> 00:31:21,700 that you're doing. 623 00:31:21,700 --> 00:31:25,090 Enzymes are classified into a bunch of different families. 624 00:31:25,090 --> 00:31:27,970 But the thing that will tell you that something 625 00:31:27,970 --> 00:31:30,040 you're reading about is an enzyme 626 00:31:30,040 --> 00:31:36,580 is the suffix ASE at the end of the name of the enzyme. 627 00:31:36,580 --> 00:31:40,720 So the enzyme that hydrolyzes the peptide bond 628 00:31:40,720 --> 00:31:44,970 or hydrolyzes proteins is called, 629 00:31:44,970 --> 00:31:49,570 no big surprise, a protease. 630 00:31:49,570 --> 00:31:53,490 And you'll see later on ribonuclease, DNAs, 631 00:31:53,490 --> 00:31:57,480 oxidoreductases, all kinds of reactions 632 00:31:57,480 --> 00:32:00,300 where if you see this term at the end of the name 633 00:32:00,300 --> 00:32:03,160 it's telling you quite loud and clear that it's an enzyme. 634 00:32:03,160 --> 00:32:06,000 Just a very sort of simple way of remembering that. 635 00:32:06,000 --> 00:32:23,610 Now enzymes promote reactions in order 636 00:32:23,610 --> 00:32:26,670 that we can have them carried out at room temperature. 637 00:32:26,670 --> 00:32:31,080 But we want to think about how they carry out these changes 638 00:32:31,080 --> 00:32:32,430 and transformations. 639 00:32:32,430 --> 00:32:35,250 What is it about the structure of the protein that 640 00:32:35,250 --> 00:32:36,930 enables these reactions? 641 00:32:36,930 --> 00:32:38,580 But the first thing we have to do 642 00:32:38,580 --> 00:32:41,790 is take a look at the thermodynamics and kinetics 643 00:32:41,790 --> 00:32:43,230 of a transformation. 644 00:32:43,230 --> 00:32:47,280 So before I go anywhere, what I want to do 645 00:32:47,280 --> 00:32:50,040 is describe to you how enzymes work 646 00:32:50,040 --> 00:32:53,010 by thinking about the physical parameters 647 00:32:53,010 --> 00:32:56,940 that we describe the energetics of a transformation. 648 00:32:56,940 --> 00:33:01,080 So in thermodynamics, you all know 649 00:33:01,080 --> 00:33:06,660 delta G is delta H minus T delta S. 650 00:33:06,660 --> 00:33:09,690 And we're really only going to worry about one of these terms. 651 00:33:09,690 --> 00:33:12,880 We're going to worry about delta G, and I'll explain why. 652 00:33:12,880 --> 00:33:17,330 So delta G is the Gibbs free energy. 653 00:33:25,316 --> 00:33:33,800 H is the enthalpy T is the temperature in Kelvin. 654 00:33:36,820 --> 00:33:38,380 And then S is entropy. 655 00:33:43,210 --> 00:33:45,760 So these are the two terms when you're looking at an energy 656 00:33:45,760 --> 00:33:49,540 diagram, we generally think about reactions where 657 00:33:49,540 --> 00:33:55,810 we describe the y-coordinate as the change in delta G, 658 00:33:55,810 --> 00:34:01,240 the change in the free energy, and the x-coordinate is 659 00:34:01,240 --> 00:34:02,860 your reaction coordinate. 660 00:34:06,300 --> 00:34:10,620 So in going from a substrate to a product, 661 00:34:10,620 --> 00:34:13,230 we generally have a situation where 662 00:34:13,230 --> 00:34:16,770 we have a substrate at a certain energy, 663 00:34:16,770 --> 00:34:19,797 and then maybe a product at a different energy. 664 00:34:19,797 --> 00:34:21,880 And we're going to talk about the details of that. 665 00:34:21,880 --> 00:34:25,980 So why do we deal with Gibbs free energy, not enthalpy? 666 00:34:25,980 --> 00:34:26,719 Does anyone know? 667 00:34:29,909 --> 00:34:30,730 OK. 668 00:34:30,730 --> 00:34:35,710 Enthalpy describes the energies of all the bonds in a molecule. 669 00:34:35,710 --> 00:34:37,449 But when you're doing an enzyme-catalyzed 670 00:34:37,449 --> 00:34:39,850 transformation, you're not busting open 671 00:34:39,850 --> 00:34:40,810 all of those bonds. 672 00:34:40,810 --> 00:34:43,820 You're not breaking something down to carbon, hydrogen, 673 00:34:43,820 --> 00:34:47,590 and oxygen. You're only dealing with parts of the energetics 674 00:34:47,590 --> 00:34:48,670 of the molecule. 675 00:34:48,670 --> 00:34:51,190 You're only dealing with what's known as the free energy 676 00:34:51,190 --> 00:34:52,270 changes. 677 00:34:52,270 --> 00:34:53,860 So looking at the enthalpy changes 678 00:34:53,860 --> 00:34:55,340 isn't going to get you very far. 679 00:34:55,340 --> 00:34:57,460 It's not going to describe the reaction 680 00:34:57,460 --> 00:34:59,770 because the enthalpy changes would be enormous 681 00:34:59,770 --> 00:35:01,130 breaking down that molecule. 682 00:35:01,130 --> 00:35:03,490 And that's not what you want to achieve. 683 00:35:03,490 --> 00:35:07,780 In a chemical transformation, we care about delta G. 684 00:35:07,780 --> 00:35:10,090 Now the next thing to think about is 685 00:35:10,090 --> 00:35:12,190 what are the energetics of the reaction, 686 00:35:12,190 --> 00:35:15,760 and how does an enzyme-catalyzed reaction manipulate 687 00:35:15,760 --> 00:35:19,040 those energetics? 688 00:35:19,040 --> 00:35:22,460 So the key thing here is we want to talk 689 00:35:22,460 --> 00:35:26,140 about Gibbs free energy. 690 00:35:26,140 --> 00:35:28,880 I shouldn't have written quite this much stuff here 691 00:35:28,880 --> 00:35:33,675 because I need the Blackboard. 692 00:35:33,675 --> 00:35:34,820 All right. 693 00:35:34,820 --> 00:35:40,440 So when you describe a reaction, you 694 00:35:40,440 --> 00:35:45,570 want to understand how far that reaction goes 695 00:35:45,570 --> 00:35:49,570 and how fast that reaction goes. 696 00:35:49,570 --> 00:35:51,390 So when you go through a reaction, 697 00:35:51,390 --> 00:35:55,470 we can describe how far the reaction goes 698 00:35:55,470 --> 00:35:59,280 by thinking about the free energy of the substrates 699 00:35:59,280 --> 00:36:00,580 and the products. 700 00:36:00,580 --> 00:36:04,260 So in this case, the substrate is at a higher energy 701 00:36:04,260 --> 00:36:05,730 than the products. 702 00:36:05,730 --> 00:36:08,670 So you will go a long way through the reaction 703 00:36:08,670 --> 00:36:12,720 to make quite a lot of products in a transformation. 704 00:36:12,720 --> 00:36:16,410 So that describes how far the reaction goes. 705 00:36:16,410 --> 00:36:26,340 So that is the difference between the energy 706 00:36:26,340 --> 00:36:28,620 of the substrate and the product. 707 00:36:28,620 --> 00:36:33,720 How fast the reaction goes is described in a different part 708 00:36:33,720 --> 00:36:34,940 of this diagram. 709 00:36:34,940 --> 00:36:37,430 Does anyone know what it is? 710 00:36:37,430 --> 00:36:37,930 Yes. 711 00:36:37,930 --> 00:36:39,013 AUDIENCE: Activation rate. 712 00:36:39,013 --> 00:36:40,120 PROFESSOR: Yes, exactly. 713 00:36:40,120 --> 00:36:43,660 How fast the reaction goes is literally 714 00:36:43,660 --> 00:36:46,120 how high the mountain is that you 715 00:36:46,120 --> 00:36:50,800 have to get over to carry out the transformation. 716 00:36:50,800 --> 00:36:55,120 And that height is described as the energy of activation. 717 00:36:55,120 --> 00:36:58,540 So that tells you how fast, and the difference here 718 00:36:58,540 --> 00:37:00,070 tells you how far. 719 00:37:00,070 --> 00:37:04,000 The energy of activation is a really important parameter 720 00:37:04,000 --> 00:37:06,910 because it's actually what gets manipulated when you're dealing 721 00:37:06,910 --> 00:37:08,980 with catalyzed reactions. 722 00:37:08,980 --> 00:37:10,840 So the energy of activation-- 723 00:37:10,840 --> 00:37:14,320 the higher that mountain is, the slower the reaction 724 00:37:14,320 --> 00:37:16,480 will be because it's a much harder transformation 725 00:37:16,480 --> 00:37:17,710 to go through. 726 00:37:17,710 --> 00:37:22,060 The reactions in our bodies can be of different flavors 727 00:37:22,060 --> 00:37:24,850 depending on the difference in energy 728 00:37:24,850 --> 00:37:26,920 of the substrate and the product. 729 00:37:26,920 --> 00:37:31,650 So shown there, substrate going to product 730 00:37:31,650 --> 00:37:34,830 where the product is at lower energy than the substrate, 731 00:37:34,830 --> 00:37:38,400 we would call this an exergonic reaction 732 00:37:38,400 --> 00:37:43,620 because we're releasing energy in the transformation. 733 00:37:43,620 --> 00:37:48,855 So S higher than P. Exergonic. 734 00:37:52,540 --> 00:37:54,700 And if we have a different reaction-- 735 00:37:54,700 --> 00:37:56,380 and I'll sketch this one in here-- 736 00:38:02,340 --> 00:38:05,940 where the product is higher energy-- 737 00:38:05,940 --> 00:38:08,090 and this is a reaction coordinate-- 738 00:38:08,090 --> 00:38:16,065 then that will be an endergonic reaction. 739 00:38:21,480 --> 00:38:24,780 Both reactions happen in enzyme-catalyzed systems. 740 00:38:24,780 --> 00:38:27,660 And we'll explain why you're able to catalyze 741 00:38:27,660 --> 00:38:30,210 even ones that require energy. 742 00:38:30,210 --> 00:38:32,610 So exergonic releases energy. 743 00:38:44,502 --> 00:38:50,510 And endergonic requires. 744 00:38:54,510 --> 00:38:55,010 OK. 745 00:38:59,590 --> 00:39:01,510 What else have I got on here? 746 00:39:01,510 --> 00:39:05,470 We also, in the situations where energy is produced, 747 00:39:05,470 --> 00:39:10,730 the exergonic reactions, we call these catabolic processes. 748 00:39:10,730 --> 00:39:12,880 And if you have trouble remembering 749 00:39:12,880 --> 00:39:15,040 catabolic and anabolic, just join me in 750 00:39:15,040 --> 00:39:17,320 that because I always forget which is which. 751 00:39:17,320 --> 00:39:21,160 But the ones that produce energy are catabolic. 752 00:39:21,160 --> 00:39:25,690 The ones that require energy are anabolic. 753 00:39:25,690 --> 00:39:28,180 And when we think about metabolism, 754 00:39:28,180 --> 00:39:31,480 the catabolic reactions are when we're breaking molecules down 755 00:39:31,480 --> 00:39:32,770 because we need energy. 756 00:39:32,770 --> 00:39:35,370 We need to use it to do something. 757 00:39:35,370 --> 00:39:37,990 The anabolic reactions are when we want to store things. 758 00:39:37,990 --> 00:39:40,690 Store fats, build proteins, because they're 759 00:39:40,690 --> 00:39:41,890 going to be endergonic. 760 00:39:41,890 --> 00:39:45,310 They're going to be requiring energy to take place. 761 00:39:45,310 --> 00:39:48,590 I just forgot one thing that I have shamefully done. 762 00:39:48,590 --> 00:39:52,270 Remember, this axis is kilocalories per mole 763 00:39:52,270 --> 00:39:55,540 most commonly when we're talking about delta G, 764 00:39:55,540 --> 00:39:58,000 or kilojoules per mole if you're in a different part 765 00:39:58,000 --> 00:39:58,570 of the world. 766 00:39:58,570 --> 00:40:02,270 But it's important to have units on these diagrams. 767 00:40:02,270 --> 00:40:04,480 So that tells us a little bit about 768 00:40:04,480 --> 00:40:06,440 enzyme-catalyzed reactions. 769 00:40:06,440 --> 00:40:11,500 We need the enzyme to do something 770 00:40:11,500 --> 00:40:13,900 about this energy of activation. 771 00:40:13,900 --> 00:40:16,390 Because if we didn't have a high energy of activation 772 00:40:16,390 --> 00:40:18,760 and I brought a Snickers bar to eat during class, 773 00:40:18,760 --> 00:40:21,160 I would just burst into flames, right? 774 00:40:21,160 --> 00:40:23,830 It needs a high energy of activation 775 00:40:23,830 --> 00:40:28,090 to keep it stable under regular conditions, 776 00:40:28,090 --> 00:40:31,870 but only break down the bonds at times when 777 00:40:31,870 --> 00:40:33,520 you require that breakdown. 778 00:40:37,342 --> 00:40:38,470 All right. 779 00:40:38,470 --> 00:40:40,420 So what did the catalyst do? 780 00:40:52,860 --> 00:40:53,960 OK. 781 00:40:53,960 --> 00:40:57,020 Now I'll show you the simple reaction. 782 00:40:57,020 --> 00:40:59,090 The enzymes are a very large structure. 783 00:40:59,090 --> 00:41:01,430 It binds to a substrate, chemistry happens, 784 00:41:01,430 --> 00:41:03,350 and it releases a product. 785 00:41:03,350 --> 00:41:06,830 But at the same time, you can't disobey the principles 786 00:41:06,830 --> 00:41:08,010 of thermodynamics. 787 00:41:08,010 --> 00:41:10,160 So there are certain criteria we have 788 00:41:10,160 --> 00:41:14,330 to think about when we consider an enzyme-catalyzed reaction. 789 00:41:14,330 --> 00:41:19,760 So first of all, do not disobey whichever law of thermodynamics 790 00:41:19,760 --> 00:41:20,420 it is. 791 00:41:20,420 --> 00:41:28,910 They do not change delta G. Delta 792 00:41:28,910 --> 00:41:31,340 G is a property of the two reactants. 793 00:41:31,340 --> 00:41:34,100 You're not going to change it with a catalyst. 794 00:41:34,100 --> 00:41:38,510 It's going to have a much more, a more important impact 795 00:41:38,510 --> 00:41:39,800 on a different parameter. 796 00:41:39,800 --> 00:41:44,130 Which parameter do enzymes change and help lower? 797 00:41:44,130 --> 00:41:44,630 Over there. 798 00:41:44,630 --> 00:41:45,872 AUDIENCE: [INAUDIBLE] 799 00:41:45,872 --> 00:41:46,580 PROFESSOR: Right. 800 00:41:46,580 --> 00:41:54,200 So catalysts do change and in fact 801 00:41:54,200 --> 00:41:56,730 lower energy of activation. 802 00:41:56,730 --> 00:41:58,970 And we'll talk about how they do that the end. 803 00:41:58,970 --> 00:42:01,760 And then the last rule about a catalyst 804 00:42:01,760 --> 00:42:12,410 is you can recover them unchanged after a reaction. 805 00:42:12,410 --> 00:42:14,800 It would be a lousy catalyst if it did its chemistry 806 00:42:14,800 --> 00:42:17,180 and then you've used up the catalyst. 807 00:42:17,180 --> 00:42:20,290 So enzyme catalysis are the ultimate green reagents. 808 00:42:20,290 --> 00:42:22,150 You can keep using them thousands 809 00:42:22,150 --> 00:42:25,570 and thousands of times to continuously turnover 810 00:42:25,570 --> 00:42:26,500 transformation. 811 00:42:26,500 --> 00:42:29,020 So you haven't changed a catalyst. 812 00:42:29,020 --> 00:42:31,510 So the things that we want to think about is how-- 813 00:42:31,510 --> 00:42:35,170 what are the processes that enzymes can manipulate? 814 00:42:41,667 --> 00:42:43,250 And I should probably just quickly run 815 00:42:43,250 --> 00:42:46,228 through these slides so we've talked about these entities. 816 00:42:46,228 --> 00:42:48,020 But I put them on the board because they're 817 00:42:48,020 --> 00:42:50,220 particularly important. 818 00:42:50,220 --> 00:42:53,750 So the energy of activation of a catalyzed reaction 819 00:42:53,750 --> 00:42:55,690 is lower than the uncatalyzed. 820 00:42:55,690 --> 00:42:58,130 And I'm not going to bore you with these questions 821 00:42:58,130 --> 00:43:01,230 because you can work this out quite readily. 822 00:43:01,230 --> 00:43:04,250 So delta G is the free energy that changes. 823 00:43:04,250 --> 00:43:07,850 And these are endergonic because the energy of the products 824 00:43:07,850 --> 00:43:08,750 is lower. 825 00:43:08,750 --> 00:43:11,360 So this is the slide I want to get to with respect 826 00:43:11,360 --> 00:43:13,640 to the enzyme-- 827 00:43:13,640 --> 00:43:15,200 to enzyme catalysis. 828 00:43:15,200 --> 00:43:17,270 So we always think, well, gosh, the enzyme 829 00:43:17,270 --> 00:43:20,240 is really large relative to the size of the product. 830 00:43:20,240 --> 00:43:23,520 That's because all the energy within the protein-folded 831 00:43:23,520 --> 00:43:26,840 structure is very useful for lowering 832 00:43:26,840 --> 00:43:30,090 the energy of activation of a transformation. 833 00:43:30,090 --> 00:43:32,090 So let's say I have a reaction that 834 00:43:32,090 --> 00:43:37,370 involves two substrates coming together to make a product. 835 00:43:37,370 --> 00:43:40,370 If I'm off the enzyme, these guys, 836 00:43:40,370 --> 00:43:42,920 it's going to take them a long time to bump into each other 837 00:43:42,920 --> 00:43:44,900 to do chemistry. 838 00:43:44,900 --> 00:43:47,900 The way enzymes catalyze those types of reactions 839 00:43:47,900 --> 00:43:51,800 is they have binding sites for both of those compounds. 840 00:43:51,800 --> 00:43:54,230 In fact, the enzyme acts as a stage. 841 00:43:54,230 --> 00:43:56,540 One substrate binds. 842 00:43:56,540 --> 00:43:58,010 The other substrate binds. 843 00:43:58,010 --> 00:44:01,070 They're binding close to each other on the enzyme. 844 00:44:01,070 --> 00:44:02,660 Chemistry can happen. 845 00:44:02,660 --> 00:44:07,070 It favors reactions that involve multiple molecules. 846 00:44:07,070 --> 00:44:11,210 What about another situation where you have a bond-- 847 00:44:11,210 --> 00:44:15,700 for example, the amide bond-- 848 00:44:15,700 --> 00:44:17,810 the proteases break? 849 00:44:17,810 --> 00:44:21,140 It's hard to think of how that-- how can we make that more easy? 850 00:44:21,140 --> 00:44:23,330 Well, amides are most stable when 851 00:44:23,330 --> 00:44:28,820 they are flat and planar through this arrangement of atoms. 852 00:44:28,820 --> 00:44:30,260 But what can happen on the enzyme 853 00:44:30,260 --> 00:44:34,820 is that they can twist bonds to make them less stable and then 854 00:44:34,820 --> 00:44:36,770 more easy to hydrolyze. 855 00:44:36,770 --> 00:44:39,830 So the structure of that enzyme basically holds 856 00:44:39,830 --> 00:44:44,000 onto the substrate and twists or distorts the bond 857 00:44:44,000 --> 00:44:46,250 that you're trying to do chemistry on 858 00:44:46,250 --> 00:44:49,760 to once again lower the energy of activation. 859 00:44:49,760 --> 00:44:52,580 Another way enzymes work is in a reaction where 860 00:44:52,580 --> 00:44:54,740 you're breaking this bond, you might 861 00:44:54,740 --> 00:44:57,050 make charged intermediates. 862 00:44:57,050 --> 00:45:00,590 The enzyme's there to hold those charged intermediates 863 00:45:00,590 --> 00:45:02,420 in order to stabilize them. 864 00:45:02,420 --> 00:45:05,240 Once again, to lower energy of activation. 865 00:45:05,240 --> 00:45:07,670 So it's funny when you get the question that's well, 866 00:45:07,670 --> 00:45:09,830 how do enzymes catalyze reactions? 867 00:45:09,830 --> 00:45:11,570 There is no one rule. 868 00:45:11,570 --> 00:45:13,550 You want to think about the reactions 869 00:45:13,550 --> 00:45:17,180 and then just think about the ways in which an enzyme could 870 00:45:17,180 --> 00:45:18,710 contribute to that. 871 00:45:18,710 --> 00:45:21,110 For example, orienting two substrates 872 00:45:21,110 --> 00:45:23,300 ready to do chemistry. 873 00:45:23,300 --> 00:45:26,990 Causing physical strain in a bond that you want to break. 874 00:45:26,990 --> 00:45:33,380 Or comforting electric charges that form during a reaction 875 00:45:33,380 --> 00:45:34,382 coordinate. 876 00:45:34,382 --> 00:45:36,590 So there are loads and loads of different principles, 877 00:45:36,590 --> 00:45:41,090 and it's a really important study that is carried out. 878 00:45:41,090 --> 00:45:45,020 So finally, I think I have a couple-- 879 00:45:45,020 --> 00:45:47,150 oh no, I have a couple of minutes. 880 00:45:47,150 --> 00:45:49,350 But I want to just describe this to you. 881 00:45:49,350 --> 00:45:51,050 It'll also be covered in the sections, 882 00:45:51,050 --> 00:45:54,110 because I'm going to rush it a bit because this last bit 883 00:45:54,110 --> 00:45:56,810 features a little bit on the P set. 884 00:45:56,810 --> 00:46:02,300 So finally, enzymes are very commonly the targets of drugs. 885 00:46:02,300 --> 00:46:05,780 We like to think that some drugs are important targets. 886 00:46:05,780 --> 00:46:09,200 If we deactivate the enzyme, we might mitigate 887 00:46:09,200 --> 00:46:11,060 the symptoms of a disease. 888 00:46:11,060 --> 00:46:13,580 Now you can't go in and heat the enzyme 889 00:46:13,580 --> 00:46:17,790 or denature the enzyme if you're trying to treat a person. 890 00:46:17,790 --> 00:46:21,170 So we do a lot of work to mitigate disease 891 00:46:21,170 --> 00:46:24,510 by inhibiting enzymes with small molecules. 892 00:46:24,510 --> 00:46:26,690 So in these slides, I describe to you 893 00:46:26,690 --> 00:46:30,830 the types of molecules that may alter the chemistry 894 00:46:30,830 --> 00:46:32,610 of a transformation. 895 00:46:32,610 --> 00:46:36,090 So if a substrate binds to an enzyme-active side-- 896 00:46:36,090 --> 00:46:38,180 we often do this Pac-Man rendition-- 897 00:46:38,180 --> 00:46:41,390 you could design a molecule that binds there instead 898 00:46:41,390 --> 00:46:45,210 and basically inhibits the substrate from getting there. 899 00:46:45,210 --> 00:46:50,420 This would be called a simple reversible inhibitor that's 900 00:46:50,420 --> 00:46:53,090 competitive with the active site. 901 00:46:53,090 --> 00:46:56,570 There are other inhibitors that will bind to the enzyme 902 00:46:56,570 --> 00:47:00,950 but do chemistry with it and stay blocked at the enzyme. 903 00:47:00,950 --> 00:47:04,190 And that would be called an irreversible competitive 904 00:47:04,190 --> 00:47:04,970 inhibitor. 905 00:47:04,970 --> 00:47:06,950 You can't get the inhibitor off. 906 00:47:06,950 --> 00:47:09,730 And there's differences in the way you can reverse this. 907 00:47:09,730 --> 00:47:12,890 Because for example, up here, if I add a lot more substrate 908 00:47:12,890 --> 00:47:15,470 and these are equilibria, I can get my reaction 909 00:47:15,470 --> 00:47:16,850 to happen any way. 910 00:47:16,850 --> 00:47:20,270 But here, I could add as much substrate as possible 911 00:47:20,270 --> 00:47:21,200 but it won't help. 912 00:47:21,200 --> 00:47:23,480 It won't reverse the transformation. 913 00:47:23,480 --> 00:47:24,080 OK? 914 00:47:24,080 --> 00:47:26,642 And there's a question here to restore the reaction. 915 00:47:26,642 --> 00:47:28,100 The answer really is, you just have 916 00:47:28,100 --> 00:47:31,070 to start with a new enzyme cause you covalently 917 00:47:31,070 --> 00:47:33,470 changed the protein structure. 918 00:47:33,470 --> 00:47:35,435 The last type of inhibitors that are important 919 00:47:35,435 --> 00:47:38,630 are the ones that bind at different sites on the enzymes. 920 00:47:38,630 --> 00:47:40,740 And they are called allosteric. 921 00:47:40,740 --> 00:47:42,630 Allo always means different. 922 00:47:42,630 --> 00:47:45,930 So if you have a compound that's an allosteric inhibitor, 923 00:47:45,930 --> 00:47:48,540 it might bind on another face of the enzyme, 924 00:47:48,540 --> 00:47:51,450 but it will alter the active side so it doesn't work. 925 00:47:51,450 --> 00:47:53,550 That's an allosteric inhibitor. 926 00:47:53,550 --> 00:47:57,720 And the final type of compound is an allosteric activator 927 00:47:57,720 --> 00:48:00,180 that may bind somewhere else on the enzyme 928 00:48:00,180 --> 00:48:02,100 but make it more active. 929 00:48:02,100 --> 00:48:05,490 So these are the way small molecules work. 930 00:48:05,490 --> 00:48:07,470 I'd like to encourage the TAs to just cover 931 00:48:07,470 --> 00:48:10,380 this in a little bit more detail because I've rushed It. 932 00:48:10,380 --> 00:48:12,330 And I'll also re-mention it at the beginning 933 00:48:12,330 --> 00:48:13,570 of the next class. 934 00:48:13,570 --> 00:48:16,710 But bear in mind, we should have everything covered now 935 00:48:16,710 --> 00:48:18,830 so the problem set 1. 936 00:48:18,830 --> 00:48:21,600 And if you have any questions, reach out to us. 937 00:48:21,600 --> 00:48:23,070 Covered them in section. 938 00:48:23,070 --> 00:48:26,670 And I'll reiterate a little bit of this in the next class. 939 00:48:26,670 --> 00:48:30,330 And finally, there's a little bit of reading. 940 00:48:30,330 --> 00:48:32,280 If you would like to prepare, we'll 941 00:48:32,280 --> 00:48:34,890 talk about carbohydrates next time, 942 00:48:34,890 --> 00:48:36,790 one of my favorite molecules. 943 00:48:36,790 --> 00:48:41,585 And there's also a fabulous set of videos on how enzymes work 944 00:48:41,585 --> 00:48:45,180 at the Protein Data Bank site. 945 00:48:45,180 --> 00:48:48,210 And you will see this little handout 946 00:48:48,210 --> 00:48:51,770 on the version of the slides that's posted.