1 00:00:16,290 --> 00:00:18,360 PROFESSOR: So what I want to do today is-- 2 00:00:18,360 --> 00:00:21,210 I want to introduce this to you very quickly-- 3 00:00:21,210 --> 00:00:24,900 is-- and I was going to show you this at the end of the last 4 00:00:24,900 --> 00:00:26,130 class-- 5 00:00:26,130 --> 00:00:30,990 if we simply go to the far end of the scale, the picometer 6 00:00:30,990 --> 00:00:32,729 scale-- you see carbon. 7 00:00:32,729 --> 00:00:35,700 I'm not going to start you with carbon, that is a little dull. 8 00:00:35,700 --> 00:00:38,100 But over the next few weeks-- 9 00:00:38,100 --> 00:00:43,470 few classes, rather, because we have to do this in fast order-- 10 00:00:43,470 --> 00:00:47,200 we will cover details of carbohydrates, 11 00:00:47,200 --> 00:00:51,090 amino acids nucleosides, and phospholipids 12 00:00:51,090 --> 00:00:54,420 and how those building blocks are put together-- 13 00:00:54,420 --> 00:00:58,380 their properties, their ability to interact and engage 14 00:00:58,380 --> 00:01:02,400 in non-covalent interactions with other molecules 15 00:01:02,400 --> 00:01:05,160 and the ability to make polymers out 16 00:01:05,160 --> 00:01:09,420 of some of these, such as the nucleosides and the amino acids 17 00:01:09,420 --> 00:01:11,760 and the carbohydrates, which then start 18 00:01:11,760 --> 00:01:14,170 to create the richness of life. 19 00:01:14,170 --> 00:01:18,690 We will also discuss today the super molecular chemistry 20 00:01:18,690 --> 00:01:22,080 of phospholipids as they make micelles and lipid 21 00:01:22,080 --> 00:01:25,520 bilayers, which are the key boundary of cells. 22 00:01:25,520 --> 00:01:26,928 So this is very important. 23 00:01:26,928 --> 00:01:28,470 And then in the following week, we'll 24 00:01:28,470 --> 00:01:34,020 go to some of the bigger things like proteins, nucleic acid, 25 00:01:34,020 --> 00:01:36,480 polymers-- for example, here's RNA. 26 00:01:36,480 --> 00:01:39,660 So the course will literally do this-- 27 00:01:39,660 --> 00:01:41,940 take you from one end of the scale to the other. 28 00:01:41,940 --> 00:01:44,760 So I want you to get a sense of these dimensions. 29 00:01:44,760 --> 00:01:47,580 I want to mention one sort of fairly stupid thing 30 00:01:47,580 --> 00:01:50,850 with respect to how chemists and biochemists talk 31 00:01:50,850 --> 00:01:53,850 about certain metrics, certain distances that 32 00:01:53,850 --> 00:01:59,280 are pertinent to biology and biochemistry. 33 00:01:59,280 --> 00:02:04,830 Engineers tend to talk about micrometers and nanometers. 34 00:02:04,830 --> 00:02:08,850 There is one unit that chemists and biologists use quite a lot, 35 00:02:08,850 --> 00:02:13,755 it's the Angstrom after a Finnish or Sw-- 36 00:02:13,755 --> 00:02:15,270 no, not Finnish. 37 00:02:15,270 --> 00:02:17,520 I think it was a Norwegian. 38 00:02:17,520 --> 00:02:19,170 And that is equivalent-- 39 00:02:19,170 --> 00:02:23,430 10 Angstrom equals 1 nanometer. 40 00:02:23,430 --> 00:02:24,843 So when you're looking at scales, 41 00:02:24,843 --> 00:02:26,760 we tend to talk about Angstrom because they're 42 00:02:26,760 --> 00:02:28,680 a convenient number. 43 00:02:28,680 --> 00:02:30,810 But don't get fooled by this. 44 00:02:30,810 --> 00:02:33,540 It can be a little bit confusing because it's 45 00:02:33,540 --> 00:02:34,840 10 to the negative 10. 46 00:02:34,840 --> 00:02:36,600 So a nanometer is 10 to the negative 9, 47 00:02:36,600 --> 00:02:38,210 you know that quite frequently. 48 00:02:38,210 --> 00:02:41,730 Picometer-- 10 to the negative 12, micrometer-- negative 6. 49 00:02:41,730 --> 00:02:45,120 But the Angstrom is just a funny unit we use a lot, 50 00:02:45,120 --> 00:02:46,960 and it's 10 to the negative 10. 51 00:02:46,960 --> 00:02:51,090 So just to make sure there's no ambiguity about that particular 52 00:02:51,090 --> 00:02:53,100 detail, OK? 53 00:02:53,100 --> 00:02:53,940 All right. 54 00:02:53,940 --> 00:02:58,110 So today's lecture will focus on the molecules of life. 55 00:02:58,110 --> 00:03:01,560 And in particular, I'm going to, through the next few classes, 56 00:03:01,560 --> 00:03:04,947 introduce you to the various molecules of life. 57 00:03:04,947 --> 00:03:06,780 But first of all, we have to do a little bit 58 00:03:06,780 --> 00:03:09,150 to understand chemical bonding. 59 00:03:09,150 --> 00:03:10,980 And in particular, we want to look 60 00:03:10,980 --> 00:03:14,520 at both covalent and non-covalent bonding 61 00:03:14,520 --> 00:03:17,890 because covalent bonding is important-- it's the structure, 62 00:03:17,890 --> 00:03:19,170 it's the framework. 63 00:03:19,170 --> 00:03:22,380 But non-covalent bonding is what gives us dynamics. 64 00:03:22,380 --> 00:03:24,630 These are much weaker forces that 65 00:03:24,630 --> 00:03:27,480 can be broken and remade very readily that 66 00:03:27,480 --> 00:03:29,820 are essential for things like forming 67 00:03:29,820 --> 00:03:33,810 the DNA duplex, folding your proteins, 68 00:03:33,810 --> 00:03:35,850 associating the lipid bilayer. 69 00:03:35,850 --> 00:03:39,060 All of those are non-covalent forces 70 00:03:39,060 --> 00:03:41,130 and they are dynamic because they're weak, 71 00:03:41,130 --> 00:03:43,920 you can break one relatively easily as long 72 00:03:43,920 --> 00:03:46,600 as you're ready to make another one in its place. 73 00:03:46,600 --> 00:03:49,530 So I will spend a little bit of time on that. 74 00:03:49,530 --> 00:03:51,780 And then today, we'll talk about lipids and membranes. 75 00:03:51,780 --> 00:03:54,060 But first of all, let me introduce you 76 00:03:54,060 --> 00:03:57,810 to some of the molecules of life in this rendition that's done 77 00:03:57,810 --> 00:03:59,940 by David Goodsell at Scripps. 78 00:03:59,940 --> 00:04:03,690 So up in the top corner here, you look at 2.3 79 00:04:03,690 --> 00:04:07,770 is the three dimensional structure of a protein. 80 00:04:07,770 --> 00:04:09,990 It's folded into a globular state 81 00:04:09,990 --> 00:04:13,230 through non-covalent forces. 82 00:04:13,230 --> 00:04:16,410 I brought a little 3D model of a protein for you 83 00:04:16,410 --> 00:04:18,700 to look at and take a look at later. 84 00:04:18,700 --> 00:04:20,670 That was one of the suggestions I made. 85 00:04:20,670 --> 00:04:23,400 You could coordinate printing a 3D model 86 00:04:23,400 --> 00:04:25,830 as one of your later projects. 87 00:04:25,830 --> 00:04:28,980 We will learn about the forces that hold the polymer 88 00:04:28,980 --> 00:04:31,230 together-- the covalent forces. 89 00:04:31,230 --> 00:04:34,020 But then the non-covalent forces that 90 00:04:34,020 --> 00:04:35,880 make globular structures that are 91 00:04:35,880 --> 00:04:37,440 very important for function. 92 00:04:37,440 --> 00:04:40,420 They're not much use as unraveled spaghetti. 93 00:04:40,420 --> 00:04:44,250 They're way more useful as their three dimensional structure. 94 00:04:44,250 --> 00:04:47,430 Down here in the corner is a carbohydrate. 95 00:04:47,430 --> 00:04:50,460 It really looks pretty pathetic in this rendition, 96 00:04:50,460 --> 00:04:52,740 but carbohydrates have a lot of value, 97 00:04:52,740 --> 00:04:55,950 particularly in energy storage but also in things 98 00:04:55,950 --> 00:04:59,610 like the extracellular matrix and as entities 99 00:04:59,610 --> 00:05:02,910 that signal information between cells. 100 00:05:02,910 --> 00:05:05,070 There's a lot of communication done 101 00:05:05,070 --> 00:05:07,560 by cell surface carbohydrates. 102 00:05:07,560 --> 00:05:10,170 Over here you see the canonical structure 103 00:05:10,170 --> 00:05:12,240 of double stranded DNA. 104 00:05:12,240 --> 00:05:14,310 We'll look at the covalent structure 105 00:05:14,310 --> 00:05:16,580 of those single strands, but then we'll 106 00:05:16,580 --> 00:05:20,060 focus in on the non-covalent interactions that 107 00:05:20,060 --> 00:05:24,110 make the double-stranded DNA and store genetic information which 108 00:05:24,110 --> 00:05:26,090 is also central to life. 109 00:05:26,090 --> 00:05:29,180 And then lastly on this, but we'll cover this today, 110 00:05:29,180 --> 00:05:31,280 is a lipid bilayer. 111 00:05:31,280 --> 00:05:34,340 It's a fascinating supramolecule structure 112 00:05:34,340 --> 00:05:38,000 that really is at the heart of how all your cells are 113 00:05:38,000 --> 00:05:42,650 held in a compartment surrounded by a lipid bilayer. 114 00:05:42,650 --> 00:05:45,200 So by the time we start talking about those, 115 00:05:45,200 --> 00:05:48,770 you'll understand the forces that put in place that lipid 116 00:05:48,770 --> 00:05:52,430 bilayer that arguably-- and I've read articles that say this-- 117 00:05:52,430 --> 00:05:55,190 that the evolution of lipid bilayers 118 00:05:55,190 --> 00:05:58,070 is as important as the genetic code. 119 00:05:58,070 --> 00:06:01,130 Because if cells did not have a surrounding, 120 00:06:01,130 --> 00:06:04,760 did not have an inside where you could concentrate reagents 121 00:06:04,760 --> 00:06:08,720 and macromolecules and do biochemistry, 122 00:06:08,720 --> 00:06:11,590 life wouldn't exist in the same way. 123 00:06:11,590 --> 00:06:16,790 OK, so let's take a look at the composition of living systems. 124 00:06:16,790 --> 00:06:21,950 And remarkably, we are about 75% water. 125 00:06:21,950 --> 00:06:25,080 So most proteins are very hydrated. 126 00:06:25,080 --> 00:06:27,140 There's a lot of water in cells. 127 00:06:27,140 --> 00:06:30,530 There's a lot of water outside of cells in the matrix. 128 00:06:30,530 --> 00:06:33,080 And really, we sort of survive weird. 129 00:06:33,080 --> 00:06:35,682 We survive in an aqueous environment. 130 00:06:35,682 --> 00:06:37,640 And the thing that you also want to think about 131 00:06:37,640 --> 00:06:41,150 is when we think about non-covalent forces, 132 00:06:41,150 --> 00:06:44,570 these are forces put in place in water. 133 00:06:44,570 --> 00:06:48,230 We don't live on a far distant planet 134 00:06:48,230 --> 00:06:51,320 where we're in sort of liquid methane or anything like that. 135 00:06:51,320 --> 00:06:53,630 So water is critical to life. 136 00:06:53,630 --> 00:06:57,380 The establishment of the hydrosphere when Earth first 137 00:06:57,380 --> 00:06:59,630 formed, the evolutionary events that 138 00:06:59,630 --> 00:07:04,190 happen after that were really hand in hand with the fact 139 00:07:04,190 --> 00:07:06,410 that it was an aqueous environment. 140 00:07:06,410 --> 00:07:08,240 Because forces are different whether they 141 00:07:08,240 --> 00:07:12,140 are in hydrophobic environments or hydrophilic environments. 142 00:07:12,140 --> 00:07:14,480 And really, you'll start to get appreciation 143 00:07:14,480 --> 00:07:16,140 for that as we move forward. 144 00:07:16,140 --> 00:07:18,890 So this basically suggests that if I put one of you in a giant 145 00:07:18,890 --> 00:07:23,060 desiccator and pumped out all the water I could possibly pull 146 00:07:23,060 --> 00:07:25,920 out, there'd be about sort of-- depending on your weight-- 147 00:07:25,920 --> 00:07:29,570 40 pounds of things left behind. 148 00:07:29,570 --> 00:07:32,000 Of what's left behind, the majority of it 149 00:07:32,000 --> 00:07:35,120 is going to be biological macromolecules-- whoops. 150 00:07:35,120 --> 00:07:37,290 And then the rest of it, that little sliver, 151 00:07:37,290 --> 00:07:42,090 are things like ions and small molecules-- calcium, magnesium, 152 00:07:42,090 --> 00:07:46,080 iron, manganese, those small inorganic ions 153 00:07:46,080 --> 00:07:48,500 as well as small molecule metabolites that are 154 00:07:48,500 --> 00:07:50,660 involved in central metabolism. 155 00:07:50,660 --> 00:07:53,000 Let's now look at the macromolecules 156 00:07:53,000 --> 00:07:57,020 and their sort of proportions relative to each other. 157 00:07:57,020 --> 00:07:59,540 The smallest sliver of the lipids, 158 00:07:59,540 --> 00:08:01,250 which we'll talk about today. 159 00:08:01,250 --> 00:08:03,560 Then you have the nucleic acids that 160 00:08:03,560 --> 00:08:05,780 are critical for information storage. 161 00:08:05,780 --> 00:08:09,440 You have proteins, which make the largest piece of the pie. 162 00:08:09,440 --> 00:08:14,320 And carbohydrates, which are is the 25%. 163 00:08:14,320 --> 00:08:16,820 So you can see how important carbohydrates 164 00:08:16,820 --> 00:08:20,330 are because of their proportion being relatively large. 165 00:08:20,330 --> 00:08:25,460 The lipid proportion, though, is small but absolutely critical, 166 00:08:25,460 --> 00:08:27,282 harking back to the membrane bilayer. 167 00:08:27,282 --> 00:08:29,240 Because if we didn't have the membrane bilayer, 168 00:08:29,240 --> 00:08:31,580 once again, we wouldn't have life in the same way 169 00:08:31,580 --> 00:08:32,750 that we have it now. 170 00:08:32,750 --> 00:08:36,809 So that gives you a sense of the relative proportions of things. 171 00:08:36,809 --> 00:08:39,710 And frankly, when I discuss the macromolecules, 172 00:08:39,710 --> 00:08:43,010 I really like to start with lipids because 173 00:08:43,010 --> 00:08:45,560 of the membrane bilayer, but because their structures are 174 00:08:45,560 --> 00:08:50,910 comparatively simple relative to amino acids and nucleic acids. 175 00:08:50,910 --> 00:08:52,460 So we can get a few of the basics 176 00:08:52,460 --> 00:08:56,150 of the chemical structures down and how we render them 177 00:08:56,150 --> 00:08:58,760 on paper so that we can do that with lipids, 178 00:08:58,760 --> 00:09:00,230 which are a little simpler. 179 00:09:00,230 --> 00:09:04,190 Now life, to a chemist, they have 180 00:09:04,190 --> 00:09:06,050 to sort of worry about this entire mess 181 00:09:06,050 --> 00:09:07,520 of the periodic table. 182 00:09:07,520 --> 00:09:10,970 But the good news for you is for biological systems, 183 00:09:10,970 --> 00:09:13,130 we deal with very focused components 184 00:09:13,130 --> 00:09:14,790 of the periodic table. 185 00:09:14,790 --> 00:09:17,570 So those biological macromolecules 186 00:09:17,570 --> 00:09:21,620 are made up largely of only six elements-- 187 00:09:21,620 --> 00:09:27,140 hydrogen, carbon, nitrogen, and oxygen, phosphorus, and sulfur. 188 00:09:27,140 --> 00:09:30,080 So that makes the amount of stuff 189 00:09:30,080 --> 00:09:34,880 you need to know about basic covalent structures way 190 00:09:34,880 --> 00:09:37,460 more simple than it is for the average chemist who 191 00:09:37,460 --> 00:09:40,730 has to worry about everything down here in the nether regions 192 00:09:40,730 --> 00:09:42,290 and-- whoops, what are you doing? 193 00:09:42,290 --> 00:09:45,380 And the things that are radioactive, 194 00:09:45,380 --> 00:09:46,690 all kinds of other things. 195 00:09:46,690 --> 00:09:48,440 You don't have to worry about any of that. 196 00:09:48,440 --> 00:09:51,140 So the covalent bonding we will talk about 197 00:09:51,140 --> 00:09:56,130 is amongst those six different elements. 198 00:09:56,130 --> 00:09:59,900 And they make up 98% of the cellular mass. 199 00:09:59,900 --> 00:10:03,110 And then the other components that are important in cells 200 00:10:03,110 --> 00:10:04,880 are some metal ions-- 201 00:10:04,880 --> 00:10:09,060 the alkali and [? alkalia ?] elements. 202 00:10:09,060 --> 00:10:12,380 So sodium, magnesium, potassium, calcium-- those are all 203 00:10:12,380 --> 00:10:14,030 quite important in life. 204 00:10:14,030 --> 00:10:16,130 And then these transition metal ions 205 00:10:16,130 --> 00:10:19,730 that are really important in enzyme catalysis, for example. 206 00:10:19,730 --> 00:10:21,720 But we will not cover very much of that. 207 00:10:21,720 --> 00:10:25,610 But those are what are known as trace elements that are very-- 208 00:10:25,610 --> 00:10:27,380 transition metal elements that are very 209 00:10:27,380 --> 00:10:29,600 important for biochemistry. 210 00:10:29,600 --> 00:10:31,910 And then last of all, there are some rogue ones 211 00:10:31,910 --> 00:10:36,310 that there's even smaller amounts in physiologic systems. 212 00:10:36,310 --> 00:10:39,950 These are things like chromium, molybdenum, and tungsten, 213 00:10:39,950 --> 00:10:41,870 selenium, and iodine. 214 00:10:41,870 --> 00:10:44,420 And of those, certain of these elements only 215 00:10:44,420 --> 00:10:46,670 are found in totally bizarre organisms. 216 00:10:46,670 --> 00:10:49,820 So for example, you and I don't have much molybdenum 217 00:10:49,820 --> 00:10:51,420 and tungsten, I don't think, unless it 218 00:10:51,420 --> 00:10:53,240 slipped in there by accident. 219 00:10:53,240 --> 00:10:56,780 But you and I definitely need selenium and iodine 220 00:10:56,780 --> 00:10:57,620 as trace elements. 221 00:10:57,620 --> 00:10:59,330 Does anyone know where iodine comes 222 00:10:59,330 --> 00:11:01,290 and figures most prominently? 223 00:11:01,290 --> 00:11:01,790 Yeah? 224 00:11:01,790 --> 00:11:02,260 AUDIENCE: Thyroid. 225 00:11:02,260 --> 00:11:03,800 PROFESSOR: Thyroid, absolutely. 226 00:11:03,800 --> 00:11:07,670 So the thyroid hormone is a small organic molecule 227 00:11:07,670 --> 00:11:10,040 with several iodines in it. 228 00:11:10,040 --> 00:11:14,090 And we need-- absolutely need-- iodine in our diet 229 00:11:14,090 --> 00:11:17,810 in order to build the thyroxine hormone that 230 00:11:17,810 --> 00:11:20,480 deals with a lot of aspects of metabolism. 231 00:11:20,480 --> 00:11:23,270 So we don't need a lot. 232 00:11:23,270 --> 00:11:25,160 And if we get too much, it's bad for you. 233 00:11:25,160 --> 00:11:27,980 But we definitely need traces of these elements. 234 00:11:27,980 --> 00:11:31,970 Now I will spend a very small amount of time 235 00:11:31,970 --> 00:11:36,140 just laying down the basics of organic chemistry bonding. 236 00:11:36,140 --> 00:11:40,130 Now who have you either taken the chemistry GIR 237 00:11:40,130 --> 00:11:43,445 or had high school chemistry quite recently? 238 00:11:43,445 --> 00:11:45,530 Is that pretty much all of you? 239 00:11:45,530 --> 00:11:48,810 And now if you didn't put your hand up, don't worry. 240 00:11:48,810 --> 00:11:51,650 We're here to bring you up to speed if you need it. 241 00:11:51,650 --> 00:11:54,770 Frankly, if you just know what's on the next two or three 242 00:11:54,770 --> 00:11:56,180 slides, you're in great shape. 243 00:11:56,180 --> 00:11:59,180 All the information that you need has been condensed . 244 00:11:59,180 --> 00:12:01,400 But if it's a little bit out of nowhere, 245 00:12:01,400 --> 00:12:03,380 you could come see me in office hours 246 00:12:03,380 --> 00:12:05,780 and I can just run through things for you 247 00:12:05,780 --> 00:12:07,700 and we can just get you up to speed. 248 00:12:07,700 --> 00:12:09,740 There is no need for pre-knowledge, 249 00:12:09,740 --> 00:12:13,200 I just need an idea of how much pre-knowledge you have. 250 00:12:13,200 --> 00:12:15,380 So when we talk about covalent bonding 251 00:12:15,380 --> 00:12:17,900 and start to think about the elements that 252 00:12:17,900 --> 00:12:20,900 are critical for life, it's important to consider 253 00:12:20,900 --> 00:12:24,030 the electronic structures of these elements 254 00:12:24,030 --> 00:12:28,790 and why they happen to be the chosen elements, OK? 255 00:12:28,790 --> 00:12:33,360 The most important thing about hydrogen, carbon, nitrogen, 256 00:12:33,360 --> 00:12:35,420 oxygen, phosphorus, and sulfur is they 257 00:12:35,420 --> 00:12:38,780 love to make covalent bonds. 258 00:12:38,780 --> 00:12:41,080 A lot of metal ions form salts, you 259 00:12:41,080 --> 00:12:45,380 know-- sodium chloride or many other different salts. 260 00:12:45,380 --> 00:12:49,370 But covalent bonds are the main structure 261 00:12:49,370 --> 00:12:50,840 of all macromolecules. 262 00:12:50,840 --> 00:12:55,130 Strong bonds between elements, such as these six 263 00:12:55,130 --> 00:12:56,930 in particular-- these six-- 264 00:12:56,930 --> 00:13:00,170 where they share electrons in covalent bonds 265 00:13:00,170 --> 00:13:02,270 rather than form ionic interactions 266 00:13:02,270 --> 00:13:04,700 where somebody gives an electron to someone else 267 00:13:04,700 --> 00:13:07,290 and you have a plus-minus type interaction. 268 00:13:07,290 --> 00:13:10,110 So these shared bonds are important for life. 269 00:13:10,110 --> 00:13:13,920 So it's good to understand why hydrogen, carbon, nitrogen, 270 00:13:13,920 --> 00:13:17,510 and oxygen, and then phosphorous and sulfur are so important. 271 00:13:17,510 --> 00:13:20,030 In order to understand the covalent bonding 272 00:13:20,030 --> 00:13:22,550 of these elements, it's useful to know 273 00:13:22,550 --> 00:13:24,710 the electronic configuration, but you 274 00:13:24,710 --> 00:13:26,300 could live without that. 275 00:13:26,300 --> 00:13:29,010 The most important thing is that covalent bonds, 276 00:13:29,010 --> 00:13:32,660 such as the one between carbon and hydrogen here, 277 00:13:32,660 --> 00:13:35,630 reflect a shared pair of electrons-- 278 00:13:35,630 --> 00:13:38,180 one from the hydrogen, one from the carbon-- 279 00:13:38,180 --> 00:13:40,550 to make a stable covalent bond. 280 00:13:40,550 --> 00:13:42,980 Because of its electronic configuration, 281 00:13:42,980 --> 00:13:46,970 carbon is neutral when it has four covalent bonds. 282 00:13:46,970 --> 00:13:50,430 Nitrogen is neutral when it has three covalent bonds. 283 00:13:50,430 --> 00:13:54,080 But there's an extra lone pair of electrons that are not 284 00:13:54,080 --> 00:13:56,660 forming bonds in neutral nitrogen. 285 00:13:56,660 --> 00:14:00,710 And oxygen is neutral when it has two covalent bonds. 286 00:14:00,710 --> 00:14:03,680 These could be with hydrogen, they could be with carbon, 287 00:14:03,680 --> 00:14:07,010 they could be with several of the other elements. 288 00:14:07,010 --> 00:14:10,832 For carbon, we don't deal with charged states of carbon 289 00:14:10,832 --> 00:14:12,290 because they're pretty high energy. 290 00:14:12,290 --> 00:14:14,560 They may be high energy intermediates 291 00:14:14,560 --> 00:14:17,030 in an enzyme catalyzed reaction, but they're not 292 00:14:17,030 --> 00:14:19,940 sitting there as high energy intermediates 293 00:14:19,940 --> 00:14:22,850 in your macromolecules. 294 00:14:22,850 --> 00:14:26,480 The key thing you want to notice is for all of these elements, 295 00:14:26,480 --> 00:14:29,450 the valence shell is complete with eight electrons. 296 00:14:29,450 --> 00:14:31,340 But these lone pairs-- 297 00:14:31,340 --> 00:14:34,520 and I-- or bunny ears, as people like to call them-- 298 00:14:34,520 --> 00:14:38,540 really feature very prominently in biochemistry and biology 299 00:14:38,540 --> 00:14:42,860 because they are places for hydrogen bonding interactions. 300 00:14:42,860 --> 00:14:46,850 So we run a lot on electrostatic hydrogen bonding 301 00:14:46,850 --> 00:14:49,070 and hydrophobic interactions. 302 00:14:49,070 --> 00:14:51,980 If we know where the lone pair electrons are, 303 00:14:51,980 --> 00:14:55,440 we know one part of a hydrogen bonding interaction. 304 00:14:55,440 --> 00:14:57,120 It turns out that in biology, we're 305 00:14:57,120 --> 00:15:00,810 mostly at pH 7 or in that range except for a few sub 306 00:15:00,810 --> 00:15:02,370 cellular compartments. 307 00:15:02,370 --> 00:15:05,820 But at pH 8, nitrogen lone pair of electrons 308 00:15:05,820 --> 00:15:10,530 will pick up a proton to become a positively charged nitrogen. 309 00:15:10,530 --> 00:15:13,210 And you'll mostly see that as a positively charged. 310 00:15:13,210 --> 00:15:19,260 So the side chain of lysine, which has an NH 3, an NH 2 311 00:15:19,260 --> 00:15:21,360 at the very end of a carbon chain, 312 00:15:21,360 --> 00:15:25,450 is most commonly protonated and positively charged. 313 00:15:25,450 --> 00:15:28,570 So it could be involved in an interaction. 314 00:15:28,570 --> 00:15:32,130 So we can consider both the neutral and the positively 315 00:15:32,130 --> 00:15:33,720 charged state of nitrogen. 316 00:15:33,720 --> 00:15:36,540 For oxygen, that oxygen lone pair 317 00:15:36,540 --> 00:15:40,260 can pick up a proton to form the hydronium ion. 318 00:15:40,260 --> 00:15:44,340 So that's a positively charged OH group. 319 00:15:44,340 --> 00:15:47,310 So it would have an extra proton, using up 320 00:15:47,310 --> 00:15:52,800 a lone pair and three hydrogens, or it could give up a proton 321 00:15:52,800 --> 00:15:55,170 to form the hydroxide ion. 322 00:15:55,170 --> 00:15:58,030 And those are the states of oxygen that are most common. 323 00:15:58,030 --> 00:16:02,730 So in that, we've kind of dispatched those first four 324 00:16:02,730 --> 00:16:04,920 of the six elements. 325 00:16:04,920 --> 00:16:07,440 Phosphorus and sulfur are a little tricky, 326 00:16:07,440 --> 00:16:08,910 but there is some good news. 327 00:16:12,520 --> 00:16:15,130 Sulfur copies oxygen, so you don't really 328 00:16:15,130 --> 00:16:17,110 have to worry too much about sulfur. 329 00:16:17,110 --> 00:16:18,850 You'll just consider it to really 330 00:16:18,850 --> 00:16:21,700 be sort of an older sibling of oxygen 331 00:16:21,700 --> 00:16:24,340 where all the chemistry is very, very similar. 332 00:16:24,340 --> 00:16:27,940 Sulfur, or the negatively charged sulfur anion, 333 00:16:27,940 --> 00:16:29,410 are both important. 334 00:16:29,410 --> 00:16:31,270 Phosphorus is different. 335 00:16:31,270 --> 00:16:33,310 Phosphorus does not tend to show up 336 00:16:33,310 --> 00:16:36,095 in the version that copies nitrogen. 337 00:16:36,095 --> 00:16:40,000 It is capable of adopting higher oxidation states. 338 00:16:40,000 --> 00:16:44,350 And all of the phosphorus you meet in biochemistry 339 00:16:44,350 --> 00:16:47,110 for the most part-- there's a few odd things in weird 340 00:16:47,110 --> 00:16:48,090 organisms-- 341 00:16:48,090 --> 00:16:51,890 is going to be in the form of an oxidized form of phosphorus, 342 00:16:51,890 --> 00:16:55,240 which generally has one, two, three, four, five 343 00:16:55,240 --> 00:16:56,770 bonds to phosphorus. 344 00:16:56,770 --> 00:16:59,350 It can take on a higher oxidation state. 345 00:16:59,350 --> 00:17:01,240 And you will see phosphorus. 346 00:17:01,240 --> 00:17:06,300 Phosphorus in the phosphate form is absolutely essential to life 347 00:17:06,300 --> 00:17:10,060 because it's the place where we store a ton of reactivity 348 00:17:10,060 --> 00:17:12,339 for the reactions of nucleotides, 349 00:17:12,339 --> 00:17:16,329 adenosine triphosphate, adenosine diphosphate, 350 00:17:16,329 --> 00:17:21,310 the phosphodiester backbone in nucleic acids, phosphorylation 351 00:17:21,310 --> 00:17:24,349 of amino acids to form phosphoproteins. 352 00:17:24,349 --> 00:17:30,100 It's always in this state with all the extra oxygens 353 00:17:30,100 --> 00:17:33,430 and that configuration of bonds, OK? 354 00:17:33,430 --> 00:17:36,520 If you know this, you've got a lot of the covalent bonds 355 00:17:36,520 --> 00:17:37,270 under control. 356 00:17:37,270 --> 00:17:38,650 So any questions about this? 357 00:17:38,650 --> 00:17:40,840 Is everyone all right? 358 00:17:40,840 --> 00:17:42,280 I know it might be-- it's probably 359 00:17:42,280 --> 00:17:44,230 a refresher for most of you. 360 00:17:44,230 --> 00:17:46,480 The next thing I just briefly want to mention 361 00:17:46,480 --> 00:17:51,520 is the most typical functional groups that 362 00:17:51,520 --> 00:17:53,920 occur in biological molecules. 363 00:18:02,865 --> 00:18:05,900 And you may, say, well, what does it mean, functional group? 364 00:18:05,900 --> 00:18:08,480 Usually it's a place where the action happens. 365 00:18:08,480 --> 00:18:10,490 If you have a large molecule that's 366 00:18:10,490 --> 00:18:14,780 a bunch of carbon-carbon and carbon-hydrogen covalent bonds, 367 00:18:14,780 --> 00:18:16,850 there's not a lot going on unless you can really 368 00:18:16,850 --> 00:18:19,880 rip those bonds apart, but they're high energy. 369 00:18:19,880 --> 00:18:22,070 But functional groups are oftentimes 370 00:18:22,070 --> 00:18:26,040 where chemistry happens or biochemistry happens. 371 00:18:26,040 --> 00:18:27,445 So there's the OH hydroxyl. 372 00:18:31,490 --> 00:18:33,590 We, as chemists and biochemists, will 373 00:18:33,590 --> 00:18:37,010 tend to use an R where we mean something else. 374 00:18:37,010 --> 00:18:38,840 So we don't write out a whole structure, 375 00:18:38,840 --> 00:18:42,320 we would just put R OH equals-- 376 00:18:42,320 --> 00:18:45,870 I'm going to just say anything. 377 00:18:45,870 --> 00:18:50,600 So for example, if R was CH 3, CH 2, you would have ethanol. 378 00:18:50,600 --> 00:18:53,900 But I'm keeping it more generic. 379 00:18:53,900 --> 00:18:58,010 The next functional group that is important 380 00:18:58,010 --> 00:19:02,240 is the carboxylate group, or the carboxyl group. 381 00:19:02,240 --> 00:19:03,660 Looks like this. 382 00:19:03,660 --> 00:19:05,203 Now when we look at these molecules, 383 00:19:05,203 --> 00:19:07,370 you always want to sort of think where the lone pair 384 00:19:07,370 --> 00:19:08,570 electrons are. 385 00:19:08,570 --> 00:19:15,080 There's two on oxygen, two on oxygen, two on oxygen. 386 00:19:15,080 --> 00:19:18,530 So that actually shows you where the rest of the electrons are. 387 00:19:18,530 --> 00:19:20,030 This is the carboxyl group. 388 00:19:23,734 --> 00:19:27,440 But in nature, in physiologic systems, 389 00:19:27,440 --> 00:19:34,930 this shows up most commonly in its anionic form. 390 00:19:34,930 --> 00:19:37,150 That's important because when we start 391 00:19:37,150 --> 00:19:41,470 to think of interactions between enzymes and their substrates, 392 00:19:41,470 --> 00:19:43,600 or the folding of proteins, we're 393 00:19:43,600 --> 00:19:46,750 thinking of something with a negative charge, not a neutral. 394 00:19:46,750 --> 00:19:53,480 So this group loses a proton to form the carboxylate group. 395 00:19:53,480 --> 00:19:56,875 And if you want to know where the lone pairs are now, 396 00:19:56,875 --> 00:19:58,000 that's what they look like. 397 00:19:58,000 --> 00:20:00,060 So those are two of the key ones. 398 00:20:00,060 --> 00:20:08,510 Let's now go to nitrogen. That is the neutral amine. 399 00:20:11,780 --> 00:20:14,060 But as I just mentioned to you, that 400 00:20:14,060 --> 00:20:25,640 will very commonly pick up a proton 401 00:20:25,640 --> 00:20:27,930 and be in the positively charged state. 402 00:20:27,930 --> 00:20:29,790 Now when I show you both of those guys 403 00:20:29,790 --> 00:20:32,790 in the positively charged state, what you could immediately 404 00:20:32,790 --> 00:20:35,850 tell me is that if I have an amino acid with one 405 00:20:35,850 --> 00:20:39,030 of these groups and a nearby amino acid with one 406 00:20:39,030 --> 00:20:44,790 of these groups, they could form an electrostatic interaction 407 00:20:44,790 --> 00:20:49,120 between themselves-- plus and minus complementing each other. 408 00:20:49,120 --> 00:20:51,053 So if you know the charge states, 409 00:20:51,053 --> 00:20:52,470 you're much better off because you 410 00:20:52,470 --> 00:20:57,090 can tell where non-covalent types of ionic or electrostatic 411 00:20:57,090 --> 00:20:58,810 interactions occur. 412 00:20:58,810 --> 00:21:00,480 So these are very important. 413 00:21:00,480 --> 00:21:02,220 Then there's the phosphate group-- 414 00:21:09,860 --> 00:21:14,660 it's often ionized-- and the sulfhydryl group. 415 00:21:14,660 --> 00:21:21,020 So phosphate-- the sulfhydryl group 416 00:21:21,020 --> 00:21:22,820 is also called the thiol group. 417 00:21:26,090 --> 00:21:29,830 And I'm sure I've spelt that wrong because hydryl-- 418 00:21:29,830 --> 00:21:30,940 they look like that. 419 00:21:30,940 --> 00:21:34,540 And the most common state of the sulfhydryl-- 420 00:21:34,540 --> 00:21:35,680 well, not the most common-- 421 00:21:35,680 --> 00:21:38,870 can also appear as the anionic structure. 422 00:21:38,870 --> 00:21:41,680 So that's the basic functional groups. 423 00:21:41,680 --> 00:21:45,710 Now there are two more functional group assemblies 424 00:21:45,710 --> 00:21:49,240 that you will see a lot in physiologic systems 425 00:21:49,240 --> 00:21:52,930 that are basically composites of some of these structures. 426 00:21:52,930 --> 00:21:55,840 Because when we have single building blocks, 427 00:21:55,840 --> 00:21:57,490 we need to join them to each other 428 00:21:57,490 --> 00:21:59,720 through different types of chemistries. 429 00:21:59,720 --> 00:22:02,200 So I want to show you the types of chemistry 430 00:22:02,200 --> 00:22:07,270 that you get by forming a composite of hydroxyl 431 00:22:07,270 --> 00:22:12,460 and a carboxyl group and a composite of a carboxyl group 432 00:22:12,460 --> 00:22:13,570 and an amide. 433 00:22:13,570 --> 00:22:15,730 Because the polymer that's the protein 434 00:22:15,730 --> 00:22:20,290 polymer has building blocks that have a means and carboxyls, 435 00:22:20,290 --> 00:22:23,830 but they're all put together into what polymeric structure 436 00:22:23,830 --> 00:22:26,540 where those groups have been joined in a condensation 437 00:22:26,540 --> 00:22:27,040 polymer. 438 00:22:27,040 --> 00:22:29,220 So let me just show you what those look like. 439 00:22:32,290 --> 00:22:34,420 And then we'll be done with the functional groups. 440 00:22:34,420 --> 00:22:43,800 So there are-- the first one-- 441 00:22:43,800 --> 00:22:52,928 because I've drawn them in this order, OK-- 442 00:22:52,928 --> 00:22:53,470 is the amide. 443 00:22:56,670 --> 00:23:13,440 And the other one is the ester. 444 00:23:16,740 --> 00:23:20,900 When you do these two reactions, if you do them in the lab, 445 00:23:20,900 --> 00:23:23,730 they're called condensation reactions 446 00:23:23,730 --> 00:23:26,940 because as you form that bond, you 447 00:23:26,940 --> 00:23:30,770 kick out a molecule of water. 448 00:23:30,770 --> 00:23:34,810 These are really important new functional groups to you 449 00:23:34,810 --> 00:23:39,590 because your proteins are held together by amide groups. 450 00:23:39,590 --> 00:23:41,450 In fact, they're so important in proteins, 451 00:23:41,450 --> 00:23:45,590 we often call them peptide groups. 452 00:23:45,590 --> 00:23:47,990 You'll see more about that on Monday. 453 00:23:47,990 --> 00:23:50,190 And the esters are really important. 454 00:23:50,190 --> 00:23:52,670 For example, in derivatives of glycerol 455 00:23:52,670 --> 00:23:55,940 that make fatty acids or phospholipids, 456 00:23:55,940 --> 00:23:58,760 you'll see esters occurring again and again. 457 00:23:58,760 --> 00:24:02,660 The other composite group that you can also see 458 00:24:02,660 --> 00:24:13,525 is with the phosphate plus an alcohol. 459 00:24:16,240 --> 00:24:18,610 And what that group looks like is as follows. 460 00:24:18,610 --> 00:24:23,110 And you're going to see this sort of endlessly 461 00:24:23,110 --> 00:24:24,220 in nucleic acids. 462 00:24:29,030 --> 00:24:32,070 Let's keep the charges all even here. 463 00:24:32,070 --> 00:24:34,590 And this is what's known as the phosphate ester. 464 00:24:42,900 --> 00:24:48,650 OK, and that is yet another condensation 465 00:24:48,650 --> 00:24:49,950 where you kick out water. 466 00:24:49,950 --> 00:24:53,710 All right, so let's just run back to this image. 467 00:24:53,710 --> 00:24:55,230 And we can sum it all up. 468 00:24:55,230 --> 00:24:58,750 Those are all the groups that I just described to you. 469 00:24:58,750 --> 00:25:01,200 And if you want, you can go back and put lone pairs 470 00:25:01,200 --> 00:25:03,000 of electrons on everything. 471 00:25:03,000 --> 00:25:05,040 And then the composite groups that I 472 00:25:05,040 --> 00:25:07,830 want to mention to you in particular 473 00:25:07,830 --> 00:25:11,990 are the amide and the ester. 474 00:25:11,990 --> 00:25:14,990 And they're very important in physiologic systems. 475 00:25:14,990 --> 00:25:18,170 They are the bond that holds together 476 00:25:18,170 --> 00:25:20,660 the biopolymer in many cases. 477 00:25:20,660 --> 00:25:24,560 Not shown on this picture is the phosphate ester-- 478 00:25:24,560 --> 00:25:26,540 I've added that this year because it's 479 00:25:26,540 --> 00:25:28,640 kind of important-- 480 00:25:28,640 --> 00:25:33,230 is a similar condensation reaction between phosphorus 481 00:25:33,230 --> 00:25:36,230 and an alcohol, and that in particular 482 00:25:36,230 --> 00:25:41,260 is the bond you'll see that holds together nucleic acids. 483 00:25:41,260 --> 00:25:44,210 And now one sort of thing that we 484 00:25:44,210 --> 00:25:46,340 won't go into a lot of detail-- 485 00:25:46,340 --> 00:25:49,100 I want you to notice that this nitrogen here 486 00:25:49,100 --> 00:25:51,050 has a lone pair of electrons. 487 00:25:51,050 --> 00:25:53,710 It picks up a proton very readily. 488 00:25:53,710 --> 00:25:58,190 The amide nitrogen is not so willing to pick up a proton 489 00:25:58,190 --> 00:26:00,500 because it messes up the rest of its chemistry. 490 00:26:00,500 --> 00:26:02,660 So that nitrogen in an amide tends 491 00:26:02,660 --> 00:26:04,790 to be observed as a neutral. 492 00:26:04,790 --> 00:26:08,090 However, that hydrogen can be involved in hydrogen bonds. 493 00:26:08,090 --> 00:26:10,880 OK, any questions about that before we 494 00:26:10,880 --> 00:26:13,416 move on to non-covalent bonds? 495 00:26:13,416 --> 00:26:15,560 Is everything clear? 496 00:26:15,560 --> 00:26:18,710 Now I try to put everything in one place 497 00:26:18,710 --> 00:26:20,420 so you have it in front of you. 498 00:26:20,420 --> 00:26:22,700 What I've put on those two slides 499 00:26:22,700 --> 00:26:26,030 is what you need to know about organic covalent bonding. 500 00:26:26,030 --> 00:26:27,950 It doesn't go beyond it. 501 00:26:27,950 --> 00:26:30,710 I will say there's a tiny bit of memorization, 502 00:26:30,710 --> 00:26:33,000 but once you commit that stuff to memory, 503 00:26:33,000 --> 00:26:35,180 you're in a good place with respect 504 00:26:35,180 --> 00:26:37,820 to understanding how the molecules of life 505 00:26:37,820 --> 00:26:39,310 are put together. 506 00:26:39,310 --> 00:26:39,810 OK. 507 00:26:42,740 --> 00:26:46,070 Now what is more important to me once we've 508 00:26:46,070 --> 00:26:49,670 put those structures in place is non-covalent bonding. 509 00:27:04,220 --> 00:27:09,140 Because to me, non-covalent bonding is synonymous with 510 00:27:09,140 --> 00:27:12,500 dynamics-- 511 00:27:12,500 --> 00:27:16,100 forces that can be readily broken and reassembled, broken 512 00:27:16,100 --> 00:27:17,360 and reassembled. 513 00:27:17,360 --> 00:27:21,140 The energy, the strength of a typical bond between two 514 00:27:21,140 --> 00:27:23,990 carbons or a carbon and a hydrogen 515 00:27:23,990 --> 00:27:32,030 is on the order of 90 to 100 kilocalories per mole. 516 00:27:32,030 --> 00:27:34,520 It takes a lot to break those bonds. 517 00:27:34,520 --> 00:27:36,890 We can't break them at will to go and do 518 00:27:36,890 --> 00:27:38,930 some biological activity. 519 00:27:38,930 --> 00:27:42,950 But the range of energies of the non-covalent bonds 520 00:27:42,950 --> 00:27:44,840 are far more modest. 521 00:27:44,840 --> 00:27:47,075 They range from-- so this is covalent. 522 00:27:50,660 --> 00:27:54,890 But the non-covalent range from 1, maybe 523 00:27:54,890 --> 00:28:00,060 to about 10 kilocalories per mole. 524 00:28:00,060 --> 00:28:02,330 So when you think about those forces, 525 00:28:02,330 --> 00:28:05,780 they're readily broken and made, broken and made. 526 00:28:05,780 --> 00:28:08,840 And what's so amazing about protein and nucleic acid 527 00:28:08,840 --> 00:28:12,290 structure is that you can gradually 528 00:28:12,290 --> 00:28:15,520 break a bond while you're making another non-covalent bond 529 00:28:15,520 --> 00:28:18,140 so you can have the dynamics of the structure that 530 00:28:18,140 --> 00:28:20,990 define a lot of its functional properties. 531 00:28:20,990 --> 00:28:24,230 Because structures are dynamic, an enzyme 532 00:28:24,230 --> 00:28:28,190 that's a composite of a lot of non-covalent interaction 533 00:28:28,190 --> 00:28:30,770 combined a substrate can gradually 534 00:28:30,770 --> 00:28:34,280 form a set of covalent bonds with that substrate 535 00:28:34,280 --> 00:28:37,430 but then can start changing the shape of that structure 536 00:28:37,430 --> 00:28:41,030 and that shape in order to go through a catalytic cycle 537 00:28:41,030 --> 00:28:44,510 to do chemistry and then to liberate products. 538 00:28:44,510 --> 00:28:50,450 That is all driven by changes in non-covalent bonding. 539 00:28:50,450 --> 00:28:53,930 Subtle changes that occur without big energy 540 00:28:53,930 --> 00:28:58,820 barriers that would be necessary to break the covalent bonds. 541 00:28:58,820 --> 00:29:02,870 So shown at the top here, you see the average bond energy 542 00:29:02,870 --> 00:29:04,550 of covalent bonds. 543 00:29:04,550 --> 00:29:07,050 This small number is something, for example, 544 00:29:07,050 --> 00:29:08,510 between two chlorines. 545 00:29:08,510 --> 00:29:09,920 That's a pretty weak bond. 546 00:29:09,920 --> 00:29:13,070 But of course, we don't have a lot of them running around. 547 00:29:13,070 --> 00:29:16,050 So really, carbon-hydrogen, carbon-carbon, 548 00:29:16,050 --> 00:29:17,780 they're at the higher end-- 549 00:29:17,780 --> 00:29:21,590 about 100 kilocalories, 80 kilocalories per mole. 550 00:29:21,590 --> 00:29:23,750 The other important interactions, though, that 551 00:29:23,750 --> 00:29:27,630 make up the non-covalent interactions are as follows. 552 00:29:27,630 --> 00:29:35,360 So the first important one is the ionic bond. 553 00:29:35,360 --> 00:29:42,080 It is also called a salt bridge or 554 00:29:42,080 --> 00:29:43,970 an electrostatic interaction. 555 00:29:46,960 --> 00:29:49,300 Why we give three names for this probably 556 00:29:49,300 --> 00:29:52,930 comes from which type of chemist decided to define them. 557 00:29:52,930 --> 00:29:55,150 They are all the same things. 558 00:29:55,150 --> 00:30:01,810 They are basically interactions between a positively charged 559 00:30:01,810 --> 00:30:06,190 entity, a protonated amine; and a negatively charged entity, 560 00:30:06,190 --> 00:30:08,350 a deprotonated carboxylate. 561 00:30:08,350 --> 00:30:11,960 Those are about the strongest of the non-covalent bonds, 562 00:30:11,960 --> 00:30:14,110 but it's very variable because it depends 563 00:30:14,110 --> 00:30:15,910 a lot on their environment. 564 00:30:15,910 --> 00:30:19,240 If those two entities are in a hydrophobic environment, 565 00:30:19,240 --> 00:30:21,640 they're going to charge right for each other 566 00:30:21,640 --> 00:30:24,610 to form a strong electrostatic interaction. 567 00:30:24,610 --> 00:30:27,550 But if those are out in water, each of those groups 568 00:30:27,550 --> 00:30:30,310 could be solvated by water and they'd 569 00:30:30,310 --> 00:30:32,230 have to give up solvation in order 570 00:30:32,230 --> 00:30:35,410 to form a good electrostatic interaction. 571 00:30:35,410 --> 00:30:37,240 When we talk about protein folding, 572 00:30:37,240 --> 00:30:39,830 we'll go into that in a little bit more detail. 573 00:30:39,830 --> 00:30:42,580 So the reason why this says very variable 574 00:30:42,580 --> 00:30:43,910 is not to drive you crazy. 575 00:30:43,910 --> 00:30:46,450 It's just they're very variable. 576 00:30:46,450 --> 00:30:49,150 But they will still range, I would say, 577 00:30:49,150 --> 00:30:53,090 from 2 to 10 kilocalories. 578 00:30:53,090 --> 00:30:54,850 Come on. 579 00:30:54,850 --> 00:30:56,710 So those are important-- easy to pick out. 580 00:30:56,710 --> 00:30:58,360 The strongest of the set. 581 00:30:58,360 --> 00:31:00,950 If Dr. Ray gives you a problem set 582 00:31:00,950 --> 00:31:04,750 and starts asking you to pick out non-covalent interactions, 583 00:31:04,750 --> 00:31:07,240 that's the one you take care of straight 584 00:31:07,240 --> 00:31:09,790 away because it is the most obvious. 585 00:31:09,790 --> 00:31:14,040 The next most important, though, is the hydrogen bond. 586 00:31:14,040 --> 00:31:20,290 Now hydrogen bonds have been known 587 00:31:20,290 --> 00:31:23,892 to mystify people for years because people 588 00:31:23,892 --> 00:31:25,600 are like, how do I pick these things out, 589 00:31:25,600 --> 00:31:26,892 how do I pick these things out? 590 00:31:26,892 --> 00:31:30,070 I'm going to give you a foolproof way of picking out 591 00:31:30,070 --> 00:31:33,370 hydrogen bonds so you will never be at a loss for hydrogen 592 00:31:33,370 --> 00:31:35,510 bonds, OK. 593 00:31:35,510 --> 00:31:37,850 Well, how do we recognize them? 594 00:31:37,850 --> 00:31:45,010 They are between hydrogens that are on electronegative elements 595 00:31:45,010 --> 00:31:46,435 such as oxygen-- 596 00:31:50,660 --> 00:31:53,080 of course, there's other things attached here-- 597 00:31:53,080 --> 00:31:59,150 or on nitrogen, or on sulfur. 598 00:31:59,150 --> 00:32:02,090 So all of those three functional groups 599 00:32:02,090 --> 00:32:05,030 can serve as hydrogen bond donors. 600 00:32:05,030 --> 00:32:09,020 They can give a proton in a hydrogen bond and share 601 00:32:09,020 --> 00:32:12,830 that proton between a hydrogen bond acceptor, OK. 602 00:32:12,830 --> 00:32:14,705 So these are all going to be known as donors. 603 00:32:19,010 --> 00:32:20,450 So you can recognize them. 604 00:32:20,450 --> 00:32:25,670 This-- carbon is not a hydrogen bond donor. 605 00:32:25,670 --> 00:32:27,500 Carbon's got his hydrogen and he's not 606 00:32:27,500 --> 00:32:29,570 giving it away to anybody for love or money. 607 00:32:29,570 --> 00:32:30,980 Its holding on tight. 608 00:32:30,980 --> 00:32:34,580 So this is not a hydrogen bond donor. 609 00:32:34,580 --> 00:32:35,420 OK? 610 00:32:35,420 --> 00:32:37,590 Now what are the hydrogen bond acceptors 611 00:32:37,590 --> 00:32:41,637 are places where that hydrogen would want to sit-- yes. 612 00:32:41,637 --> 00:32:43,470 AUDIENCE: There's the two lines next to it-- 613 00:32:45,513 --> 00:32:47,930 PROFESSOR: Actually, they just read-- they could be double 614 00:32:47,930 --> 00:32:51,050 or they could be single, but I was just putting them 615 00:32:51,050 --> 00:32:54,020 so that you see that the nitrogen has one, two, three 616 00:32:54,020 --> 00:32:55,190 bonds to it. 617 00:32:55,190 --> 00:32:56,480 OK, yeah. 618 00:32:56,480 --> 00:33:00,050 It could alternatively also be the form of nitrogen-- 619 00:33:00,050 --> 00:33:02,750 just to confuse you-- 620 00:33:02,750 --> 00:33:06,290 that has an extra proton that could be the protonated version 621 00:33:06,290 --> 00:33:09,390 because that can still be a hydrogen bond donor. 622 00:33:09,390 --> 00:33:10,070 OK. 623 00:33:10,070 --> 00:33:12,200 Now what are the hydrogen bond acceptors? 624 00:33:12,200 --> 00:33:16,050 They are any place where you have a lone pair. 625 00:33:16,050 --> 00:33:20,410 So let's just think of a carbonyl group-- 626 00:33:20,410 --> 00:33:21,840 two lone pairs. 627 00:33:21,840 --> 00:33:29,440 A hydroxyl group-- two lone pairs. 628 00:33:33,480 --> 00:33:35,960 A nitrogen that is not protonated-- 629 00:33:40,100 --> 00:33:41,300 one lone pair. 630 00:33:41,300 --> 00:33:44,070 Those are the hydrogen bond acceptors. 631 00:33:44,070 --> 00:33:47,420 So as long as you know your structures 632 00:33:47,420 --> 00:33:50,330 in the functional groups and you know where the lone pairs are, 633 00:33:50,330 --> 00:33:54,060 you can figure out where there could be a hydrogen bond. 634 00:33:54,060 --> 00:33:57,590 So all of these types are acceptors. 635 00:34:01,740 --> 00:34:02,520 OK. 636 00:34:02,520 --> 00:34:06,900 So in protein biochemistry, for example, 637 00:34:06,900 --> 00:34:11,280 those kinds of hydrogen bonding is very, very important 638 00:34:11,280 --> 00:34:14,370 to form the three-dimensional structures of proteins. 639 00:34:14,370 --> 00:34:18,210 And the reason why is because in a protein, 640 00:34:18,210 --> 00:34:25,150 proteins are made up of amide bonds 641 00:34:25,150 --> 00:34:30,290 where this Hn can be a donor, this O can be an acceptor, 642 00:34:30,290 --> 00:34:34,030 and you can get networks of hydrogen bonding interactions 643 00:34:34,030 --> 00:34:36,850 to establish structures of proteins. 644 00:34:36,850 --> 00:34:39,670 When a small molecule binds to a protein, 645 00:34:39,670 --> 00:34:41,560 it may look to fit in a place where 646 00:34:41,560 --> 00:34:45,460 it can maximize electrostatic interactions and the hydrogen 647 00:34:45,460 --> 00:34:46,960 bonding interactions. 648 00:34:46,960 --> 00:34:50,530 So we'll ask you to start to be able to pick out 649 00:34:50,530 --> 00:34:52,130 hydrogen bonding. 650 00:34:52,130 --> 00:34:57,860 So here you saw the electrostatic interaction. 651 00:34:57,860 --> 00:35:01,070 Here is a typical hydrogen bonding interaction 652 00:35:01,070 --> 00:35:04,040 between a hydroxyl and a carbonyl group. 653 00:35:04,040 --> 00:35:06,080 I couldn't spot that very readily 654 00:35:06,080 --> 00:35:08,780 unless I remembered that there were lone pairs of electrons 655 00:35:08,780 --> 00:35:10,130 there, OK. 656 00:35:10,130 --> 00:35:12,450 The other two ty-- any questions about that? 657 00:35:12,450 --> 00:35:15,200 Any questions about hydrogen bonding? 658 00:35:15,200 --> 00:35:16,820 Are you comfortable with thinking 659 00:35:16,820 --> 00:35:19,760 you could derive your way to figuring out where they are? 660 00:35:19,760 --> 00:35:21,950 You'll see them used a lot, so they'll 661 00:35:21,950 --> 00:35:26,030 become more and more familiar to you as you move forward. 662 00:35:26,030 --> 00:35:26,920 OK, good. 663 00:35:26,920 --> 00:35:34,595 The last two types of interactions 664 00:35:34,595 --> 00:35:43,880 are the hydrophobic interactions and van der Waals forces. 665 00:35:47,980 --> 00:35:51,430 I never get the spelling right, but I'll 666 00:35:51,430 --> 00:35:53,030 get the concepts over you. 667 00:35:53,030 --> 00:35:56,870 Now hydrophobic interactions are incredibly important. 668 00:35:56,870 --> 00:36:02,170 So when you think of folding a protein driven solely 669 00:36:02,170 --> 00:36:05,620 by electrostatic interactions and hydrogen bonding, 670 00:36:05,620 --> 00:36:08,760 you have a bit of a problem because all of those groups 671 00:36:08,760 --> 00:36:10,840 are hydrogen bonded to water. 672 00:36:10,840 --> 00:36:12,970 So you'd have to get rid of the water 673 00:36:12,970 --> 00:36:15,430 before they could make interactions with each other. 674 00:36:15,430 --> 00:36:16,600 Does that makes sense? 675 00:36:16,600 --> 00:36:18,320 Because we are in water. 676 00:36:18,320 --> 00:36:20,590 We're folding in water. 677 00:36:20,590 --> 00:36:23,110 Hydrophobic interactions are really great because they 678 00:36:23,110 --> 00:36:25,810 want to form in water. 679 00:36:25,810 --> 00:36:29,230 If you're making, you know, a batch of salad dressing, 680 00:36:29,230 --> 00:36:32,290 oil and vinegar, and you shake it up, what happens? 681 00:36:32,290 --> 00:36:33,760 It separates. 682 00:36:33,760 --> 00:36:36,340 The oil goes to the top, the vinegar goes to the bottom. 683 00:36:36,340 --> 00:36:37,030 Why? 684 00:36:37,030 --> 00:36:41,030 Because of hydrophobic interactions in the oil phase. 685 00:36:41,030 --> 00:36:43,630 So if you have a large protein that 686 00:36:43,630 --> 00:36:45,730 has a bunch of hydrophobic groups, 687 00:36:45,730 --> 00:36:49,120 they will want to collapse out of the water 688 00:36:49,120 --> 00:36:51,200 to interact with each other. 689 00:36:51,200 --> 00:36:53,380 And then hydrogen bonding and electrostatic 690 00:36:53,380 --> 00:36:54,880 will fall into place. 691 00:36:54,880 --> 00:36:58,810 So hydrophobic interactions are a very important and vital 692 00:36:58,810 --> 00:37:02,890 force in nature in the non-covalent bonding. 693 00:37:02,890 --> 00:37:05,410 And those are literally interactions 694 00:37:05,410 --> 00:37:09,700 amongst molecules that have a lot of CH and CC bonds. 695 00:37:09,700 --> 00:37:11,560 The final force that's shown up there 696 00:37:11,560 --> 00:37:13,505 is the van der Waals force. 697 00:37:13,505 --> 00:37:15,130 And we don't worry too much about that, 698 00:37:15,130 --> 00:37:20,020 but it is simply the interaction between very weakly polarized 699 00:37:20,020 --> 00:37:22,840 carbon-hydrogen or other types of bonds 700 00:37:22,840 --> 00:37:28,840 where there's a little bit of a dipole between the bond 701 00:37:28,840 --> 00:37:31,840 and they form little dipolar interactions. 702 00:37:31,840 --> 00:37:33,610 But mostly, I think you really want 703 00:37:33,610 --> 00:37:36,400 to focus on the electrostatic, the hydrogen 704 00:37:36,400 --> 00:37:37,930 bond, and the hydrophobic. 705 00:37:37,930 --> 00:37:40,990 These are more minor and it's a little bit of a subtlety. 706 00:37:40,990 --> 00:37:43,520 So let's focus on those three. 707 00:37:43,520 --> 00:37:48,685 All right, so with that said, the key thing for you-- 708 00:37:48,685 --> 00:37:50,060 what do you need to be able to do 709 00:37:50,060 --> 00:37:54,710 is understand them and recognize them in complex systems. 710 00:37:54,710 --> 00:37:56,240 Lastly I'm just going to leave this. 711 00:37:56,240 --> 00:37:58,040 It's going to stay in your notes. 712 00:37:58,040 --> 00:38:02,660 We in biochemistry tend to use line angle drawings. 713 00:38:02,660 --> 00:38:06,530 It's kind of complicated to draw these sort of great big things 714 00:38:06,530 --> 00:38:10,010 with all the hydrogens and oxygen and stuff spelled out, 715 00:38:10,010 --> 00:38:12,530 so we use the line angled drawing. 716 00:38:12,530 --> 00:38:15,950 There's some shown here for different molecules. 717 00:38:15,950 --> 00:38:19,520 And the rules are laid out so that you can go and just 718 00:38:19,520 --> 00:38:21,470 figure out, do a bit of practicing, 719 00:38:21,470 --> 00:38:23,360 and just figure out the line angle drawing 720 00:38:23,360 --> 00:38:24,500 and what it means. 721 00:38:24,500 --> 00:38:28,100 Basically, every line represents a bond, 722 00:38:28,100 --> 00:38:31,440 every vertex represents a carbon atom. 723 00:38:31,440 --> 00:38:33,310 But what you do show on the drawings 724 00:38:33,310 --> 00:38:36,330 are the non-carbon atoms. 725 00:38:36,330 --> 00:38:40,550 So for example, oxygen, or nitrogen. And when you show, 726 00:38:40,550 --> 00:38:44,180 you imply the hydrogens that are bonded to carbon 727 00:38:44,180 --> 00:38:46,220 but you have to show the hydrogens that 728 00:38:46,220 --> 00:38:49,250 are on nitrogen or oxygen, for example, 729 00:38:49,250 --> 00:38:52,120 and you have to figure out what your charged state might be. 730 00:38:52,120 --> 00:38:53,620 So I'm going to leave you with that. 731 00:38:53,620 --> 00:38:54,510 All right. 732 00:38:54,510 --> 00:38:55,040 OK. 733 00:38:55,040 --> 00:38:58,970 So what we've learned so far is these basic forces in biology 734 00:38:58,970 --> 00:39:03,470 are critical for the assembly of the building blocks 735 00:39:03,470 --> 00:39:05,600 of biological macromolecules. 736 00:39:05,600 --> 00:39:08,300 What I want to talk to you about now-- and we'll probably, 737 00:39:08,300 --> 00:39:10,300 because I've spent a little bit of time on that, 738 00:39:10,300 --> 00:39:12,260 spill over a little more to next week-- 739 00:39:12,260 --> 00:39:14,540 but I'm going to talk to you about the first class 740 00:39:14,540 --> 00:39:17,430 of macromolecules, which are the lipids. 741 00:39:17,430 --> 00:39:19,970 So what makes something a lipid? 742 00:39:19,970 --> 00:39:23,300 These are the most sort of complicated mixture 743 00:39:23,300 --> 00:39:24,680 of biological molecules. 744 00:39:24,680 --> 00:39:27,140 And formally, they're not really macromolecules. 745 00:39:27,140 --> 00:39:28,760 They're small molecules. 746 00:39:28,760 --> 00:39:32,390 But what's common to all of them is that they are very rich 747 00:39:32,390 --> 00:39:35,630 in carbon-carbon and carbon-hydrogen bonds 748 00:39:35,630 --> 00:39:37,380 because all of these-- 749 00:39:37,380 --> 00:39:39,680 the line angle drawings of all of these 750 00:39:39,680 --> 00:39:42,620 would suggest to you that the dominant feature of all 751 00:39:42,620 --> 00:39:45,770 these molecules is a bunch of CC and CH 752 00:39:45,770 --> 00:39:49,640 ions, which makes the molecules quite hydrophobic. 753 00:39:49,640 --> 00:39:52,970 There are no functional groups there. 754 00:39:52,970 --> 00:39:55,050 And they behave very differently. 755 00:39:55,050 --> 00:39:57,800 For example, they would have a tough time dissolving 756 00:39:57,800 --> 00:39:59,790 in water in some cases. 757 00:39:59,790 --> 00:40:02,990 And so this complicated looking set of molecules 758 00:40:02,990 --> 00:40:05,840 can be distilled out as being very rich 759 00:40:05,840 --> 00:40:08,830 in carbon-hydrogen and carbon-carbon bonds. 760 00:40:08,830 --> 00:40:11,840 And we call those collectively lipids. 761 00:40:11,840 --> 00:40:15,900 And they have a lot of different functions. 762 00:40:15,900 --> 00:40:19,550 So for example, triglycerides, such as shown here, 763 00:40:19,550 --> 00:40:23,420 with three ester bonds are storage for energy-- 764 00:40:23,420 --> 00:40:27,860 things like estradiol, things like steroids. 765 00:40:27,860 --> 00:40:32,150 They have this 6-6-6-5 arrangement of rings. 766 00:40:32,150 --> 00:40:35,075 All your steroid hormones kind of look like that. 767 00:40:35,075 --> 00:40:38,000 A lot of CH bonds. 768 00:40:38,000 --> 00:40:39,710 There are some vitamins. 769 00:40:39,710 --> 00:40:43,160 So for example, retinol is a vitamin. 770 00:40:43,160 --> 00:40:44,720 It's also a lipid. 771 00:40:44,720 --> 00:40:49,630 And then there are the phospholipids shown down here. 772 00:40:49,630 --> 00:40:53,380 I just briefly want to mention a little bit about retinal 773 00:40:53,380 --> 00:40:56,140 and retinol, which are crucial. 774 00:40:56,140 --> 00:40:59,110 Retinol is a critical vitamin. 775 00:40:59,110 --> 00:41:02,050 It comes actually from carotene, which 776 00:41:02,050 --> 00:41:03,880 is a molecule that you find in a lot 777 00:41:03,880 --> 00:41:07,120 of orange and yellow fruits, such as carrots. 778 00:41:07,120 --> 00:41:09,610 But the oxidized product of retinol 779 00:41:09,610 --> 00:41:12,370 is this lipid called retinal, which 780 00:41:12,370 --> 00:41:15,550 is central to the process of vision. 781 00:41:15,550 --> 00:41:19,750 So retinal binds to proteins that sit in the membrane. 782 00:41:19,750 --> 00:41:24,710 When light shines on them, the shape of the retinal changes. 783 00:41:24,710 --> 00:41:27,100 It goes from a particular configuration 784 00:41:27,100 --> 00:41:29,080 of the double bond to a different one. 785 00:41:29,080 --> 00:41:32,920 The shape just changes, and that sends a signal to your brain. 786 00:41:32,920 --> 00:41:36,430 So lipids are important, absolutely essential, 787 00:41:36,430 --> 00:41:39,130 in vision and sight because they are involved 788 00:41:39,130 --> 00:41:42,580 in the signaling process because their shapes change and send 789 00:41:42,580 --> 00:41:45,230 signals. 790 00:41:45,230 --> 00:41:46,550 Other types of lipids-- 791 00:41:46,550 --> 00:41:49,400 so these things-- and we call them fatty acids mostly 792 00:41:49,400 --> 00:41:53,420 because they are greasy long-chained acids 793 00:41:53,420 --> 00:41:58,760 with a long hydrophobic tail and a hydrophilic end group here. 794 00:41:58,760 --> 00:42:00,980 These molecules are also what are 795 00:42:00,980 --> 00:42:03,830 known as amphipathic because they have 796 00:42:03,830 --> 00:42:06,440 a sort of split personality. 797 00:42:06,440 --> 00:42:10,910 They have a hydrophobic moiety and a hydrophilic moiety. 798 00:42:10,910 --> 00:42:13,250 Whenever you see amphi at the beginning of a word, 799 00:42:13,250 --> 00:42:14,640 it means in both. 800 00:42:14,640 --> 00:42:19,760 So both hydrophilic and lipophilic. 801 00:42:19,760 --> 00:42:21,200 So these are important. 802 00:42:21,200 --> 00:42:23,000 And these are very important components. 803 00:42:23,000 --> 00:42:24,680 You probably heard a lot of press 804 00:42:24,680 --> 00:42:28,880 about some of the fatty acids and how bad trans fats 805 00:42:28,880 --> 00:42:32,390 are for you and how you should be careful to make sure 806 00:42:32,390 --> 00:42:37,430 your diet is rich in cis fats rather than trans fats 807 00:42:37,430 --> 00:42:41,000 because the trans fats are contributors to coronary heart 808 00:42:41,000 --> 00:42:41,970 disease. 809 00:42:41,970 --> 00:42:44,780 So you may wonder, what's the relationship between heart 810 00:42:44,780 --> 00:42:48,230 disease and these two types of lipophilic components 811 00:42:48,230 --> 00:42:49,940 which are in the body? 812 00:42:49,940 --> 00:42:52,680 So let me describe to you that relationship. 813 00:42:52,680 --> 00:42:56,930 Remember that cis fats are rich in things like the nut oils 814 00:42:56,930 --> 00:42:59,570 and fruit oils, such as olive oil. 815 00:42:59,570 --> 00:43:05,180 So coronary heart disease is associated with trans fats. 816 00:43:05,180 --> 00:43:08,000 What's the linkage, what's the biology in that? 817 00:43:08,000 --> 00:43:13,380 So the story is related to cholesterol. 818 00:43:13,380 --> 00:43:17,210 Cholesterol is a critical component in our membranes. 819 00:43:17,210 --> 00:43:19,460 The trouble is we have to be able to move cholesterol 820 00:43:19,460 --> 00:43:20,480 around. 821 00:43:20,480 --> 00:43:24,290 But it's so hydrophobic it doesn't dissolve in water, OK? 822 00:43:24,290 --> 00:43:27,740 So in the body, your cholesterol is moved around 823 00:43:27,740 --> 00:43:31,100 in the form of lipoproteins that bind to the cholesterol 824 00:43:31,100 --> 00:43:33,110 and take it to the different organs 825 00:43:33,110 --> 00:43:35,210 where it is needed, all right? 826 00:43:35,210 --> 00:43:37,100 And so the lipoproteins can either 827 00:43:37,100 --> 00:43:41,540 be low density and associate with cholesterol, 828 00:43:41,540 --> 00:43:44,480 or they can be high density, and those also 829 00:43:44,480 --> 00:43:46,400 associate with cholesterol. 830 00:43:46,400 --> 00:43:50,240 The high density lipoproteins are kind of large. 831 00:43:50,240 --> 00:43:51,560 In fact, they're fairly agile. 832 00:43:51,560 --> 00:43:55,340 They don't stick to arteries and vessels, 833 00:43:55,340 --> 00:43:57,200 and they can be excreted in the liver 834 00:43:57,200 --> 00:44:00,020 or move around the bloodstream without any problem. 835 00:44:00,020 --> 00:44:03,440 It's the low density ones that are problems because they're 836 00:44:03,440 --> 00:44:05,780 low density and they kind of stick 837 00:44:05,780 --> 00:44:07,610 to the walls of your arteries and start 838 00:44:07,610 --> 00:44:10,160 making buildups and then plaques, which 839 00:44:10,160 --> 00:44:12,510 contribute to heart disease. 840 00:44:12,510 --> 00:44:15,350 So the low density ones have cholesterol, 841 00:44:15,350 --> 00:44:18,920 but they're very small, sticky, and it's a physical interaction 842 00:44:18,920 --> 00:44:22,940 with your blood vessels and they start to clog your arteries. 843 00:44:22,940 --> 00:44:26,840 What's the relationship to saturated and trans fats? 844 00:44:26,840 --> 00:44:29,630 It's that they increase the low density 845 00:44:29,630 --> 00:44:33,150 lipoprotein in preference to the high density. 846 00:44:33,150 --> 00:44:35,180 So if you have a lot of trans fats, 847 00:44:35,180 --> 00:44:37,880 you make a lot of low density lipoproteins, 848 00:44:37,880 --> 00:44:40,190 it's trying to carry cholesterol around, 849 00:44:40,190 --> 00:44:42,320 but it gets stuck to your blood vessels 850 00:44:42,320 --> 00:44:45,980 and you start to clog your blood vessels. 851 00:44:45,980 --> 00:44:48,270 That contributes to heart disease. 852 00:44:48,270 --> 00:44:50,930 So these lipophilic molecules are important. 853 00:44:50,930 --> 00:44:53,150 They are places to store energy. 854 00:44:53,150 --> 00:44:57,680 They are critical to hormones and signaling, for example. 855 00:44:57,680 --> 00:45:00,680 But there are some complications with disease 856 00:45:00,680 --> 00:45:03,260 because certain types of fatty acids 857 00:45:03,260 --> 00:45:04,790 contribute to heart disease. 858 00:45:04,790 --> 00:45:05,477 Yeah. 859 00:45:05,477 --> 00:45:07,019 AUDIENCE: Is it a lower density if it 860 00:45:07,019 --> 00:45:08,610 doesn't have a bend in it? 861 00:45:08,610 --> 00:45:10,190 PROFESSOR: No, no. 862 00:45:10,190 --> 00:45:13,550 the density is of the entire physical particle. 863 00:45:13,550 --> 00:45:18,710 It's a nanoparticle that would show a different density 864 00:45:18,710 --> 00:45:21,260 respective to how it floats in water. 865 00:45:21,260 --> 00:45:25,070 So the density is really the physical metric 866 00:45:25,070 --> 00:45:28,060 of the entire particle as opposed to just the molecule. 867 00:45:28,060 --> 00:45:30,680 It might be different because of the way it compacts, 868 00:45:30,680 --> 00:45:34,070 but the important thing about the trans fats 869 00:45:34,070 --> 00:45:36,560 is that they really contribute to making 870 00:45:36,560 --> 00:45:39,580 the protein that forms the low density particles. 871 00:45:39,580 --> 00:45:41,850 OK, all right. 872 00:45:41,850 --> 00:45:45,180 So I'm just going to introduce these-- 873 00:45:45,180 --> 00:45:48,990 not quickly, but I'll show you some cool images 874 00:45:48,990 --> 00:45:50,760 at the beginning of the next class. 875 00:45:50,760 --> 00:45:54,840 This is the last group of lipidic molecules, 876 00:45:54,840 --> 00:45:56,830 and they are actually-- 877 00:45:56,830 --> 00:45:59,970 whoops-- esters and phosphoesters 878 00:45:59,970 --> 00:46:03,100 of fatty acids with glycerol. 879 00:46:03,100 --> 00:46:05,220 This is a small molecule that forms 880 00:46:05,220 --> 00:46:09,000 esters through its oxygen to these long chains 881 00:46:09,000 --> 00:46:10,770 and also to phosphate. 882 00:46:10,770 --> 00:46:15,960 And these contribute to really important functions 883 00:46:15,960 --> 00:46:16,960 in the body. 884 00:46:16,960 --> 00:46:19,170 They are also amphipathic because they 885 00:46:19,170 --> 00:46:24,060 have a hydrophobic component and a hydrophilic component. 886 00:46:24,060 --> 00:46:27,210 And we often draw them in a shorthand form like this 887 00:46:27,210 --> 00:46:30,860 to represent this head group and these tails. 888 00:46:30,860 --> 00:46:33,870 And I want to just leave you with this wonderful image 889 00:46:33,870 --> 00:46:37,010 of the sorts of supramolecular structures 890 00:46:37,010 --> 00:46:39,850 that these kinds of phospholipids can form. 891 00:46:39,850 --> 00:46:48,660 So supramolecular is a very important term in biology 892 00:46:48,660 --> 00:46:51,180 as it is in engineering-- supramolecular. 893 00:46:54,379 --> 00:46:58,230 It means it's a structure that's above the molecular level. 894 00:46:58,230 --> 00:47:01,940 It's an aggregation of different molecules 895 00:47:01,940 --> 00:47:04,850 to make a super molecule with different properties 896 00:47:04,850 --> 00:47:07,190 from the individual components. 897 00:47:07,190 --> 00:47:18,400 Phospholipids self-assemble-- and that's another important 898 00:47:18,400 --> 00:47:18,900 term-- 899 00:47:18,900 --> 00:47:23,040 into supramolecular structures that are very, very important 900 00:47:23,040 --> 00:47:24,360 in living systems. 901 00:47:24,360 --> 00:47:29,430 Some of them just are useful in other sorts of engineering 902 00:47:29,430 --> 00:47:32,310 approaches, such as liposomes and micelles, 903 00:47:32,310 --> 00:47:35,250 but the most important supramolecular structure 904 00:47:35,250 --> 00:47:38,160 of a phospholipid is the lipid bilayer 905 00:47:38,160 --> 00:47:40,120 that surrounds your cells. 906 00:47:40,120 --> 00:47:43,500 And what happens is you simply put those molecules-- 907 00:47:43,500 --> 00:47:45,540 the phospholipids in water and they 908 00:47:45,540 --> 00:47:48,900 will self-assemble on their own into these supramolecular 909 00:47:48,900 --> 00:47:50,050 structures. 910 00:47:50,050 --> 00:47:54,570 Whether they form micelles or liposomes or bilayers 911 00:47:54,570 --> 00:47:59,280 is dependent very much on the tails of the lipids-- 912 00:47:59,280 --> 00:48:01,950 what sorts of shapes and structures you get. 913 00:48:01,950 --> 00:48:04,980 But in physiology-- in human physiology-- 914 00:48:04,980 --> 00:48:06,780 the phospholipids that we have want 915 00:48:06,780 --> 00:48:10,170 to form these bilayer structures that have incredibly 916 00:48:10,170 --> 00:48:11,770 important properties. 917 00:48:11,770 --> 00:48:14,520 Most importantly that they are semi-permeable 918 00:48:14,520 --> 00:48:18,450 and they can wrap, form the boundary to certain cells. 919 00:48:18,450 --> 00:48:20,910 So I will continue with the final discussion 920 00:48:20,910 --> 00:48:23,520 of this on Monday before we move forward 921 00:48:23,520 --> 00:48:26,220 to the amino acids, peptides, and proteins. 922 00:48:26,220 --> 00:48:29,490 And I just quickly want to move you to ask you 923 00:48:29,490 --> 00:48:34,140 for Monday to try to catch a read of the section 3.2 924 00:48:34,140 --> 00:48:35,850 in the text if you have a chance. 925 00:48:35,850 --> 00:48:38,180 It'll give you a nice preview.