1 00:00:11,070 --> 00:00:14,480 PROFESSOR: Here is the game plan for the next 2 00:00:14,480 --> 00:00:16,180 two or three lectures. 3 00:00:16,180 --> 00:00:21,460 I'm going to start by talking about the chemical forces that 4 00:00:21,460 --> 00:00:25,070 are important for the structure and function of 5 00:00:25,070 --> 00:00:27,010 these biomolecules. 6 00:00:27,010 --> 00:00:31,800 And then I'm going to relate them, as we go along, to how 7 00:00:31,800 --> 00:00:37,920 these properties influence the characteristics of these key 8 00:00:37,920 --> 00:00:39,530 macromolecules. 9 00:00:39,530 --> 00:00:49,150 And in particular we'll be talking about covalent bonds, 10 00:00:49,150 --> 00:00:59,640 hydrogen bonds, ionic bonds, a force known as van der Waals 11 00:00:59,640 --> 00:01:03,610 forces, and something that's not really a force but it's a 12 00:01:03,610 --> 00:01:06,170 characteristic that's very important, particularly when 13 00:01:06,170 --> 00:01:09,760 we think about proteins and lipids, called 14 00:01:09,760 --> 00:01:11,010 hydrophobicity-- 15 00:01:17,140 --> 00:01:20,400 literally "fear of water." 16 00:01:20,400 --> 00:01:23,810 And then the order of the molecules. 17 00:01:23,810 --> 00:01:28,200 As we talk, I'll talk about carbohydrates first. 18 00:01:30,960 --> 00:01:33,710 I'll try and get to that today. 19 00:01:33,710 --> 00:01:47,590 Then we'll talk about proteins, nucleic acids, and 20 00:01:47,590 --> 00:01:49,390 lipids, in that order. 21 00:01:49,390 --> 00:01:53,170 As you'll see, these two will be sufficient to understand 22 00:01:53,170 --> 00:01:55,130 most of the characteristics of carbohydrates. 23 00:01:55,130 --> 00:01:59,630 Whereas we're going to need all five of these to be able 24 00:01:59,630 --> 00:02:04,890 to get an intelligent understanding of 25 00:02:04,890 --> 00:02:06,695 how proteins work. 26 00:02:06,695 --> 00:02:08,789 Now, I'll caution you. 27 00:02:08,789 --> 00:02:10,209 It's going to seem-- 28 00:02:10,209 --> 00:02:12,780 God, he's going to talk about covalent bonds, as everybody 29 00:02:12,780 --> 00:02:15,190 is rolling their eyes. 30 00:02:15,190 --> 00:02:18,530 I heard about covalent bonds in grade one or something. 31 00:02:18,530 --> 00:02:24,140 But the difference here is that we're going to be looking 32 00:02:24,140 --> 00:02:27,720 at some of these forces, some of which you've been exposed 33 00:02:27,720 --> 00:02:31,900 to already, but from a biological perspective. 34 00:02:31,900 --> 00:02:33,770 And I hope if you kind of watch that, you'll begin to 35 00:02:33,770 --> 00:02:35,650 see that you're looking at something that may be sort of 36 00:02:35,650 --> 00:02:36,560 familiar to you. 37 00:02:36,560 --> 00:02:39,060 But you have to start thinking about it in a different way 38 00:02:39,060 --> 00:02:41,910 once you start thinking of what are the implications of 39 00:02:41,910 --> 00:02:44,510 the properties of these forces and the way these molecules 40 00:02:44,510 --> 00:02:48,110 behave for biology. 41 00:02:48,110 --> 00:02:52,350 So, begin with the one that everybody undoubtedly knows, 42 00:02:52,350 --> 00:02:59,780 which are covalent bonds. 43 00:02:59,780 --> 00:03:03,370 And this is the principal force 44 00:03:03,370 --> 00:03:07,410 that holds atoms together. 45 00:03:07,410 --> 00:03:13,220 And it's based on sharing electrons. 46 00:03:13,220 --> 00:03:16,130 And as I'll say, these are very strong bonds. 47 00:03:16,130 --> 00:03:20,720 And so in the simplest sort of example, hydrogen atom has one 48 00:03:20,720 --> 00:03:23,710 unpaired electron, a carbon has four. 49 00:03:23,710 --> 00:03:32,630 And so you can make methane, CH4. 50 00:03:32,630 --> 00:03:37,840 And commonly in chemistry and biology we use a line to 51 00:03:37,840 --> 00:03:39,465 represent a pair of electrons. 52 00:03:42,510 --> 00:03:44,570 So there's methane. 53 00:03:44,570 --> 00:03:49,160 As I said, apart from you know it burns, if you go out in a 54 00:03:49,160 --> 00:03:52,790 swamp or in a beach and you see bubbles, muddy bottom 55 00:03:52,790 --> 00:03:56,980 coming up, those are bubbles of methane made by methanogens 56 00:03:56,980 --> 00:03:59,810 that are living in the anaerobic layer underneath. 57 00:03:59,810 --> 00:04:02,470 A cow has a special fermentation, 58 00:04:02,470 --> 00:04:05,720 digestion cavity inside. 59 00:04:05,720 --> 00:04:08,630 It's huge, called a rumen, stuff sloshing around. 60 00:04:08,630 --> 00:04:12,240 And it's full of archaea, that are methanogens. 61 00:04:12,240 --> 00:04:16,329 And a cow makes about 400 liters of methane a day. 62 00:04:16,329 --> 00:04:19,440 And Penny will tell you, it's a very bad greenhouse gas. 63 00:04:19,440 --> 00:04:22,740 It's much more potent than carbon dioxide. 64 00:04:22,740 --> 00:04:29,710 And so the typical length of a covalent bond is about 1.5 to 65 00:04:29,710 --> 00:04:33,190 0.2 nanometers. 66 00:04:33,190 --> 00:04:40,830 And I hope you'll try and begin to get a sense of the 67 00:04:40,830 --> 00:04:42,180 links of some of these things, too. 68 00:04:42,180 --> 00:04:58,700 But the key point about this is to break a carbon-carbon 69 00:04:58,700 --> 00:05:06,550 bond needs 83 kilocalories per mole. 70 00:05:06,550 --> 00:05:10,000 So that's a lot of energy. 71 00:05:10,000 --> 00:05:15,950 At 25 degrees centigrade, if you take, say, a typical 72 00:05:15,950 --> 00:05:25,040 vibrational mode of a covalent bond, the energy that it has 73 00:05:25,040 --> 00:05:32,110 is about 0.6 kcals per mole. 74 00:05:32,110 --> 00:05:37,020 So what that means is that covalent bonds don't break on 75 00:05:37,020 --> 00:05:41,510 their own under physiological conditions. 76 00:05:41,510 --> 00:05:51,680 They can bend, they can rotate, and they can stretch. 77 00:05:51,680 --> 00:05:54,590 So they're back and forth this way, they can go this way, 78 00:05:54,590 --> 00:05:57,420 this way, but they don't break. 79 00:05:57,420 --> 00:06:04,740 And so this sort of leads to another topic that we'll talk 80 00:06:04,740 --> 00:06:06,410 about, which is utterly key-- 81 00:06:06,410 --> 00:06:10,720 It's one of the secrets of how life works-- 82 00:06:10,720 --> 00:06:14,740 are these protein molecules that are known as enzymes. 83 00:06:14,740 --> 00:06:17,890 And we'll also talk a little bit about a similar thing made 84 00:06:17,890 --> 00:06:21,210 of RNA called a ribozyme. 85 00:06:21,210 --> 00:06:38,340 But what these are are biological catalysts that 86 00:06:38,340 --> 00:06:47,000 enable specific bonds-- and this is important-- 87 00:06:47,000 --> 00:07:06,280 specific bonds to be broken or formed under physiological 88 00:07:06,280 --> 00:07:07,530 conditions. 89 00:07:10,010 --> 00:07:11,910 And this part is so important. 90 00:07:11,910 --> 00:07:14,850 If you're trying to work out a chemical reaction, the 91 00:07:14,850 --> 00:07:19,410 original process for taking nitrogen gas and making 92 00:07:19,410 --> 00:07:25,840 ammonia, the Haber process, involved some very, very tough 93 00:07:25,840 --> 00:07:28,260 molecule to break the bond of. 94 00:07:28,260 --> 00:07:32,310 So just heat it up to 500 degrees and put in a catalyst. 95 00:07:32,310 --> 00:07:33,810 But if you're a living organism, you 96 00:07:33,810 --> 00:07:34,990 don't have that option. 97 00:07:34,990 --> 00:07:40,453 You have to continually make and break bonds under the 98 00:07:40,453 --> 00:07:43,160 conditions -- the very, very narrow conditions where life 99 00:07:43,160 --> 00:07:45,170 is possible. 100 00:07:45,170 --> 00:07:47,710 If you go a little too high, things like proteins unfold. 101 00:07:47,710 --> 00:07:52,380 And then they don't work as properly as machines anymore. 102 00:07:52,380 --> 00:07:57,880 So we'll be talking more about that as we go along. 103 00:07:57,880 --> 00:08:00,590 There are different types of covalent bonds. 104 00:08:00,590 --> 00:08:03,700 And again, the first part of this isn't 105 00:08:03,700 --> 00:08:04,500 going to surprise you. 106 00:08:04,500 --> 00:08:09,290 There are single bonds, like this. 107 00:08:09,290 --> 00:08:16,140 There are double bonds, and triple. 108 00:08:18,822 --> 00:08:19,716 Excuse me. 109 00:08:19,716 --> 00:08:21,615 I'll just stay with carbon for the moment. 110 00:08:26,100 --> 00:08:31,030 The more electrons that are shared, the stronger the bond. 111 00:08:31,030 --> 00:08:39,260 And these two are referred to, if it's a carbon compound, as 112 00:08:39,260 --> 00:08:43,919 being unsaturated bonds, the same term you hear when you 113 00:08:43,919 --> 00:08:45,950 hear about unsaturated fats. 114 00:08:45,950 --> 00:08:48,540 And what that means is a fat with an unsaturation, that's 115 00:08:48,540 --> 00:08:52,130 unsaturated, will have somewhere in it a double bond, 116 00:08:52,130 --> 00:08:55,640 or in some cases, many double bonds. 117 00:08:55,640 --> 00:08:59,390 However, there's another aspect of this which might not 118 00:08:59,390 --> 00:09:02,020 have been relevant to you, but you'll see it becomes relevant 119 00:09:02,020 --> 00:09:05,550 for thinking about proteins as soon as the next lecture. 120 00:09:05,550 --> 00:09:14,090 And that is, a single bond is able to rotate this way. 121 00:09:14,090 --> 00:09:22,190 These guys can't rotate. 122 00:09:22,190 --> 00:09:26,330 And that, as you'll see, becomes important in quite a 123 00:09:26,330 --> 00:09:28,240 variety of situations. 124 00:09:28,240 --> 00:09:32,540 But we'll run into a very important example of that when 125 00:09:32,540 --> 00:09:38,990 we're thinking about the very backbone of all proteins, the 126 00:09:38,990 --> 00:09:42,500 peptide bond, which is at the heart of being a protein. 127 00:09:42,500 --> 00:09:44,970 There are other molecules that have more than one bond that 128 00:09:44,970 --> 00:09:45,520 are important. 129 00:09:45,520 --> 00:09:47,402 Oxygen is one. 130 00:09:47,402 --> 00:09:50,020 And nitrogen, as I said, is a 131 00:09:50,020 --> 00:09:53,195 particularly hard nut to crack. 132 00:09:56,220 --> 00:10:00,400 Most organisms, as I said the other day, are unable 133 00:10:00,400 --> 00:10:02,590 to break this bond. 134 00:10:02,590 --> 00:10:04,530 The only organisms that have learned how 135 00:10:04,530 --> 00:10:06,310 to do it are bacteria. 136 00:10:06,310 --> 00:10:09,760 The vast majority of them use one, single enzyme called 137 00:10:09,760 --> 00:10:12,620 nitrogenase that evolved that's a very complicated 138 00:10:12,620 --> 00:10:16,070 enzyme and has very, very stringent requirements and 139 00:10:16,070 --> 00:10:18,070 needs a huge energy input. 140 00:10:18,070 --> 00:10:20,580 But it is able to crack this bond and get 141 00:10:20,580 --> 00:10:22,800 it made into ammonia. 142 00:10:22,800 --> 00:10:27,060 But it's an example of another molecule that has a triple 143 00:10:27,060 --> 00:10:29,538 bond in it. 144 00:10:29,538 --> 00:10:32,090 Let's see, how are we doing here? 145 00:10:32,090 --> 00:10:32,950 Okay. 146 00:10:32,950 --> 00:10:45,130 So another aspect of these covalent bonds that you need 147 00:10:45,130 --> 00:10:48,440 to think about has to do with when you're 148 00:10:48,440 --> 00:10:50,340 thinking about carbon. 149 00:10:50,340 --> 00:10:54,240 And it's a property called chirality. 150 00:10:54,240 --> 00:11:01,120 And it comes from the fact that carbon has four bonds but 151 00:11:01,120 --> 00:11:04,600 they come out as a tetrahedron. 152 00:11:04,600 --> 00:11:08,220 So that doesn't matter in the case of methane. 153 00:11:08,220 --> 00:11:11,560 But I'm going to depict the tetrahedron in this way, so 154 00:11:11,560 --> 00:11:13,760 that this bond is coming -- 155 00:11:13,760 --> 00:11:16,930 these two are in the plane of the board, this one's coming 156 00:11:16,930 --> 00:11:19,030 out, that one's going back. 157 00:11:19,030 --> 00:11:21,160 And let's just put on four different substituents. 158 00:11:23,670 --> 00:11:37,160 Now if I get the mirror image of that, we will have-- 159 00:11:43,550 --> 00:11:45,820 these two molecules are called optical isomers. 160 00:11:52,260 --> 00:11:56,800 And if you sit down and play with this, you will find you 161 00:11:56,800 --> 00:12:02,290 can't convert one to the other without actually physically 162 00:12:02,290 --> 00:12:04,130 breaking a bond. 163 00:12:04,130 --> 00:12:09,510 And this is really important, one of the central concepts 164 00:12:09,510 --> 00:12:13,400 that I hope you might remember from this course because it 165 00:12:13,400 --> 00:12:17,270 cuts across a lot of the stuff talk we'll be talking about. 166 00:12:23,060 --> 00:12:39,500 At a molecular level, much of biology relies on the 167 00:12:39,500 --> 00:12:50,350 interaction of complementary 3D surfaces. 168 00:12:54,410 --> 00:12:58,720 We're actually very familiar with this at a macro level in 169 00:12:58,720 --> 00:13:00,610 our own lives. 170 00:13:00,610 --> 00:13:04,070 Imagine you've just come back from the party late on 171 00:13:04,070 --> 00:13:05,815 Saturday night, you're crossing the Mass. 172 00:13:05,815 --> 00:13:09,590 Ave. Bridge, the wind is howling, you're freezing. 173 00:13:09,590 --> 00:13:11,365 But no problem, you've got your gloves. 174 00:13:11,365 --> 00:13:16,170 And you reach in your pocket and you have two left gloves. 175 00:13:16,170 --> 00:13:21,070 No matter what you do, you can't get that right hand to 176 00:13:21,070 --> 00:13:23,750 fit properly into the left-handed glove. 177 00:13:27,640 --> 00:13:29,125 One's a mirror image of the other. 178 00:13:29,125 --> 00:13:32,260 But we run into this problem even in our own lives. 179 00:13:32,260 --> 00:13:37,750 When you saw how that DNA had fit right into a 180 00:13:37,750 --> 00:13:42,450 groove in the protein. 181 00:13:42,450 --> 00:13:44,635 If we had a mirror image of the DNA or we had a mirror 182 00:13:44,635 --> 00:13:46,430 image of the protein, it wouldn't work. 183 00:13:46,430 --> 00:13:51,790 This principle goes all the way through biology. 184 00:13:51,790 --> 00:13:56,580 There is another characteristic of covalent 185 00:13:56,580 --> 00:14:04,120 bonds that becomes important again. 186 00:14:04,120 --> 00:14:10,040 And that is how equally the electrons are sharing. 187 00:14:10,040 --> 00:14:11,740 So again, it goes back to the sharing of 188 00:14:11,740 --> 00:14:14,290 electrons, but with a twist. 189 00:14:14,290 --> 00:14:20,930 If we have a carbon-carbon or a carbon-hydrogen bond, it's 190 00:14:20,930 --> 00:14:23,100 pretty much equal sharing. 191 00:14:23,100 --> 00:14:28,710 And this is known as a nonpolar bond. 192 00:14:34,230 --> 00:14:41,725 But if you have a nitrogen or an oxygen bond, it's unequal. 193 00:14:46,770 --> 00:14:50,350 And these are known as polar bonds. 194 00:14:50,350 --> 00:14:56,740 And the term that's used to describe this unequal sharing 195 00:14:56,740 --> 00:15:08,210 of electrons is known as the electronegativity of the atom. 196 00:15:08,210 --> 00:15:12,240 It's basically a word that means the greediness of a 197 00:15:12,240 --> 00:15:14,790 particular atom for electrons. 198 00:15:14,790 --> 00:15:19,490 So if you have an oxygen and a hydrogen bond, although we 199 00:15:19,490 --> 00:15:21,680 write it like that on the board and you've undoubtedly 200 00:15:21,680 --> 00:15:25,790 seen this for many years in chemistry, in fact, the 201 00:15:25,790 --> 00:15:29,780 electrons spend more time down here than they spend up there. 202 00:15:29,780 --> 00:15:34,450 So there's a little bit of a negative charge on the oxygen 203 00:15:34,450 --> 00:15:37,840 and a little bit of a plus charge on the hydrogen. 204 00:15:37,840 --> 00:15:41,030 That's usually represented by a little delta to indicate 205 00:15:41,030 --> 00:15:46,760 that this has a wee bit of negative charge, that has a 206 00:15:46,760 --> 00:15:50,270 wee bit of positive charge. 207 00:15:50,270 --> 00:15:53,540 And a molecule that's very important with 208 00:15:53,540 --> 00:15:56,710 respect to this is water. 209 00:15:56,710 --> 00:15:59,315 Because water, as you know, is H2O. 210 00:15:59,315 --> 00:16:01,390 But it's not symmetrical. 211 00:16:01,390 --> 00:16:04,570 The angle here is 104.5 degrees. 212 00:16:04,570 --> 00:16:10,210 And so the oxygen has a little bit of a negative charge but 213 00:16:10,210 --> 00:16:13,960 each of these has a little bit of a plus charge. 214 00:16:13,960 --> 00:16:20,550 Actually, water is 55 molar. 215 00:16:20,550 --> 00:16:24,440 So it's a little dipole. 216 00:16:24,440 --> 00:16:30,510 You've got 55 molar, these little dipoles going on. 217 00:16:30,510 --> 00:16:34,430 This property of electronegativity and nonpolar 218 00:16:34,430 --> 00:16:42,090 bonds then leads to the second of the forces that we're going 219 00:16:42,090 --> 00:16:43,680 to be talking about. 220 00:16:43,680 --> 00:16:47,428 That's force number two. 221 00:16:47,428 --> 00:16:56,210 And that's a hydrogen, or H bond. 222 00:16:56,210 --> 00:17:06,829 And this is a bond that's made possible by a little bit of a 223 00:17:06,829 --> 00:17:11,200 negative charge that's on oxygen, or nitrogen, or a few 224 00:17:11,200 --> 00:17:16,352 other molecules and a little bit of a positive charge 225 00:17:16,352 --> 00:17:21,270 that's due to the hydrogen that's in a polar bond. 226 00:17:24,140 --> 00:17:38,400 This is very important, as you'll see, for proteins, 227 00:17:38,400 --> 00:17:48,160 nucleic acids, and for carbohydrates. 228 00:17:48,160 --> 00:17:51,330 And it has a huge amount to do with the 229 00:17:51,330 --> 00:17:53,240 way that water behaves. 230 00:17:53,240 --> 00:17:57,590 Because in that 55-molar water, you'll have one water 231 00:17:57,590 --> 00:18:02,830 molecule that's going to be like this. 232 00:18:02,830 --> 00:18:06,255 And there will be another water molecule down here with 233 00:18:06,255 --> 00:18:07,670 a little bit of a negative charge. 234 00:18:10,530 --> 00:18:14,880 And this a little bit of a plus charge on this hydrogen 235 00:18:14,880 --> 00:18:19,860 and a little bit of a negative charge can form what's known 236 00:18:19,860 --> 00:18:23,500 as a hydrogen bond between them. 237 00:18:23,500 --> 00:18:27,060 And what's especially important about these hydrogen 238 00:18:27,060 --> 00:18:40,270 bonds is they're about 1/20 the strength 239 00:18:40,270 --> 00:18:42,110 of a covalent bond. 240 00:18:42,110 --> 00:18:45,320 And that means that in a distribution of molecules at 241 00:18:45,320 --> 00:18:49,463 physiological temperatures, there will be some guys up in 242 00:18:49,463 --> 00:18:52,360 the -- the most energetic molecules within the bunch 243 00:18:52,360 --> 00:18:57,330 will have enough energy to break hydrogen bonds. 244 00:18:57,330 --> 00:18:58,830 But they're much easier to do. 245 00:18:58,830 --> 00:19:02,430 And just to peer ahead, when we talk about replicating DNA, 246 00:19:02,430 --> 00:19:06,270 those two strands are held together by hydrogen bonds. 247 00:19:06,270 --> 00:19:09,860 So the backbones are really solid, just like two strips of 248 00:19:09,860 --> 00:19:10,870 Velcro or something. 249 00:19:10,870 --> 00:19:15,490 But the hydrogen bonds hold the two strands together, but 250 00:19:15,490 --> 00:19:16,660 1/20 the strength. 251 00:19:16,660 --> 00:19:19,960 So it's basically like molecular Velcro between the 252 00:19:19,960 --> 00:19:21,850 two strands of DNA. 253 00:19:21,850 --> 00:19:28,500 And we'll see some more examples of this. 254 00:19:28,500 --> 00:19:29,943 Let's see if I can go back to this and get 255 00:19:29,943 --> 00:19:30,900 this thing to play. 256 00:19:30,900 --> 00:19:34,730 This is static representation just illustrating this. 257 00:19:34,730 --> 00:19:38,580 But in fact, what happens, water molecules are 258 00:19:38,580 --> 00:19:40,160 continually changing partners. 259 00:19:40,160 --> 00:19:43,770 So they're constantly making shells, and cages, and so on. 260 00:19:43,770 --> 00:19:49,430 And the next little movie is a picosecond simulation of water 261 00:19:49,430 --> 00:19:50,760 just at zero degrees. 262 00:19:50,760 --> 00:19:54,250 And you can see how the molecules are changing 263 00:19:54,250 --> 00:19:56,440 partners, making little shells and things. 264 00:19:56,440 --> 00:20:00,490 And here's a picosecond simulation of water at the 265 00:20:00,490 --> 00:20:01,225 boiling temperature. 266 00:20:01,225 --> 00:20:03,790 And what you can see from this is every now and then, a 267 00:20:03,790 --> 00:20:07,020 molecule like this one will get enough energy to break out 268 00:20:07,020 --> 00:20:09,010 of this constant sharing of little 269 00:20:09,010 --> 00:20:14,820 hydrogen bonds and escape. 270 00:20:14,820 --> 00:20:17,870 And another thing, when we talk about getting something 271 00:20:17,870 --> 00:20:20,170 dissolved in water, this is something we'll 272 00:20:20,170 --> 00:20:20,940 have to think about. 273 00:20:20,940 --> 00:20:23,800 Because if you try and dissolve something in water, 274 00:20:23,800 --> 00:20:27,270 like stir a lot of oil into it, you know what happens. 275 00:20:27,270 --> 00:20:29,510 You can stir like mad and doesn't go in. 276 00:20:29,510 --> 00:20:32,890 Part of the problem is if you put something in the water, 277 00:20:32,890 --> 00:20:36,210 it's going to have to break these existing hydrogen bonds. 278 00:20:36,210 --> 00:20:37,920 And that's an energy cost. 279 00:20:37,920 --> 00:20:39,880 So in order to get something to dissolve, you're going to 280 00:20:39,880 --> 00:20:41,490 have to get the energy back. 281 00:20:41,490 --> 00:20:42,630 And we'll be talking about that. 282 00:20:42,630 --> 00:20:46,800 But it's one of the fundamental parts of water. 283 00:20:46,800 --> 00:20:49,760 You're familiar with the characteristics of water. 284 00:20:49,760 --> 00:20:51,390 There's surface tension. 285 00:20:51,390 --> 00:20:54,920 It's why trees can grow 300 feet tall, because they've got 286 00:20:54,920 --> 00:20:57,330 basically little nanotubes and little capillaries. 287 00:20:57,330 --> 00:21:01,620 And with this surface tension, water, due to hydrogen bonds, 288 00:21:01,620 --> 00:21:03,120 can go 300 feet up. 289 00:21:03,120 --> 00:21:04,490 The water can go right up. 290 00:21:04,490 --> 00:21:07,470 You've seen water bugs walk around on water. 291 00:21:07,470 --> 00:21:11,100 There's a particularly interesting lizard in South 292 00:21:11,100 --> 00:21:14,800 America, Central America called the basilisk lizard 293 00:21:14,800 --> 00:21:17,250 that's about 2 and 1/2 feet long. 294 00:21:20,520 --> 00:21:22,530 It's able to run across the top of the water. 295 00:21:22,530 --> 00:21:25,900 It's actually called the Jesus Christ lizard. 296 00:21:25,900 --> 00:21:29,030 And it's able to do that because of this surface 297 00:21:29,030 --> 00:21:30,300 tension in the water. 298 00:21:30,300 --> 00:21:33,160 In fact, when I finished my Ph.D. Thesis, I went in a 299 00:21:33,160 --> 00:21:34,610 competition for the theses. 300 00:21:34,610 --> 00:21:37,490 And mine was something like, a chemical enzymatic synthesis 301 00:21:37,490 --> 00:21:39,310 of oligoribonucleotides. 302 00:21:39,310 --> 00:21:42,870 And I was competing against a guy who said why do lizards 303 00:21:42,870 --> 00:21:46,280 run on water, and his entire talk consisted of movies of 304 00:21:46,280 --> 00:21:48,510 this thing running across the water. 305 00:21:48,510 --> 00:21:50,970 I thought I was toast, but I actually won that prize. 306 00:21:50,970 --> 00:21:53,090 But anyway, every time I see this I remember it. 307 00:21:56,010 --> 00:21:58,380 For example, when they go and explore Mars or think about 308 00:21:58,380 --> 00:22:00,350 planets, they're always looking for water because it 309 00:22:00,350 --> 00:22:03,300 has this very, very special set of properties that are so 310 00:22:03,300 --> 00:22:04,980 important for life.