1 00:00:11,740 --> 00:00:17,160 HAZEL SIVE: Another truism of biochemistry is that many of 2 00:00:17,160 --> 00:00:20,870 the molecules within cells are very large. 3 00:00:20,870 --> 00:00:21,940 And they're called 4 00:00:21,940 --> 00:00:24,700 macromolecules, to indicate this. 5 00:00:24,700 --> 00:00:25,950 So macromolecules. 6 00:00:38,380 --> 00:00:38,680 So these are often -- 7 00:00:38,680 --> 00:00:41,540 Biological molecules are often macromolecules. 8 00:00:41,540 --> 00:00:47,225 And these macromolecules are often polymers-- 9 00:00:49,900 --> 00:00:51,600 not always-- 10 00:00:51,600 --> 00:01:00,830 where a polymer is some kind of repeat of 11 00:01:00,830 --> 00:01:03,435 a monomer "n" times. 12 00:01:06,350 --> 00:01:11,030 And in formation of macromolecules, there are two 13 00:01:11,030 --> 00:01:13,970 kinds of reactions that you need to know. 14 00:01:13,970 --> 00:01:17,820 They are called condensation and hydrolysis reactions. 15 00:01:30,500 --> 00:01:32,240 And they go something like this. 16 00:01:32,240 --> 00:01:35,395 Condensation reactions form bonds. 17 00:01:39,750 --> 00:01:44,230 Hydrolysis reactions break bonds. 18 00:01:44,230 --> 00:01:48,050 And condensation reactions go something like this. 19 00:01:48,050 --> 00:01:53,120 If we call the monomer M, there would be a monomer with 20 00:01:53,120 --> 00:01:58,730 a hydroxyl group that interacts with another monomer 21 00:01:58,730 --> 00:02:00,950 that has a hydroxyl group. 22 00:02:00,950 --> 00:02:12,130 And the outcome of that would be a bond between the two 23 00:02:12,130 --> 00:02:16,390 monomers, with the release of water. 24 00:02:16,390 --> 00:02:20,450 And the flip of that, during a hydrolysis reaction, is 25 00:02:20,450 --> 00:02:28,340 exactly the opposite, where this dimonomer here, M-O-M, 26 00:02:28,340 --> 00:02:31,030 where there's an ether bond between the two monomers as 27 00:02:31,030 --> 00:02:33,550 I've drawn it, called different things-- we'll talk 28 00:02:33,550 --> 00:02:34,550 about that-- 29 00:02:34,550 --> 00:02:39,050 adds water and then is broken down into two monomers. 30 00:02:39,050 --> 00:02:43,220 And so you should know a condensation and a hydrolysis 31 00:02:43,220 --> 00:02:46,900 reaction, because every reaction that we talk about in 32 00:02:46,900 --> 00:02:51,780 this course and in much of biochemistry involves either 33 00:02:51,780 --> 00:02:55,800 condensation or hydrolysis reactions. 34 00:02:55,800 --> 00:03:01,540 Often, both condensation or hydrolysis require energy, 35 00:03:01,540 --> 00:03:04,290 sometimes that they release it. 36 00:03:04,290 --> 00:03:17,145 So often, both often require energy in order to proceed. 37 00:03:17,145 --> 00:03:18,395 Okay. 38 00:03:24,160 --> 00:03:25,410 Very good. 39 00:03:27,520 --> 00:03:30,900 Let's move then to the second topic that I'd like to discuss 40 00:03:30,900 --> 00:03:34,030 today, which is the first big class of 41 00:03:34,030 --> 00:03:36,500 macromolecules, the lipids. 42 00:03:50,410 --> 00:03:55,020 Lipids are a fascinating class of macromolecules 43 00:03:55,020 --> 00:03:56,790 essential for life. 44 00:03:56,790 --> 00:04:06,780 They comprise about 5% of the dry mass of a cell, the dry 45 00:04:06,780 --> 00:04:10,530 mass referring to the mass remaining after the water has 46 00:04:10,530 --> 00:04:12,070 been removed. 47 00:04:12,070 --> 00:04:14,700 And lipids are crucial-- 48 00:04:14,700 --> 00:04:17,290 and we discussed this briefly last lecture-- 49 00:04:17,290 --> 00:04:21,079 for formation of the membranes around the cell and around the 50 00:04:21,079 --> 00:04:23,080 various organelles. 51 00:04:23,080 --> 00:04:28,640 So lipids are required for membranes. 52 00:04:34,100 --> 00:04:37,780 They also serve as major energy stores for the cells. 53 00:04:37,780 --> 00:04:40,280 Their bonds are very energy rich. 54 00:04:40,280 --> 00:04:44,080 They are also involved in various signaling processes. 55 00:04:44,080 --> 00:04:47,280 We'll touch on this today and later in the course. 56 00:04:47,280 --> 00:04:51,710 And of course, they are involved in insulation, both 57 00:04:51,710 --> 00:04:54,590 in keeping the whole organism warm-- if it's an animal, 58 00:04:54,590 --> 00:04:55,780 during winter-- 59 00:04:55,780 --> 00:05:00,560 but also in insulating nerve cells as nerve cells transmit 60 00:05:00,560 --> 00:05:03,900 their signals by insulating them, kind of like an 61 00:05:03,900 --> 00:05:07,970 electrical wire is insulated by plastic. 62 00:05:07,970 --> 00:05:11,210 The condensation reactions that form during lipid 63 00:05:11,210 --> 00:05:16,600 formation often involve synthesis of things called 64 00:05:16,600 --> 00:05:18,810 triglycerides. 65 00:05:18,810 --> 00:05:22,580 And triglycerides are formed from glycerol. 66 00:05:38,450 --> 00:05:41,540 And I'm going to warn you that my chemical structures are 67 00:05:41,540 --> 00:05:43,580 going to be casual. 68 00:05:43,580 --> 00:05:47,090 We assume that you have enough chemistry that if you know 69 00:05:47,090 --> 00:05:50,700 that I write CH2OH, you actually know that the 70 00:05:50,700 --> 00:05:54,320 hydrogens are sticking out around the carbon. 71 00:05:54,320 --> 00:05:54,470 Okay? 72 00:05:54,470 --> 00:05:56,460 That's my contract with you. 73 00:05:56,460 --> 00:05:59,770 We assume you know enough chemistry to deal with that. 74 00:05:59,770 --> 00:06:03,440 If you don't, then please come and see me or Dr. Sinha. 75 00:06:03,440 --> 00:06:08,710 And to that glycerol is added a fatty acid. 76 00:06:08,710 --> 00:06:16,050 And the fatty acid has got a hydroxyl group attached to a 77 00:06:16,050 --> 00:06:24,490 carbonyl, which is attached to a long-chain hydrocarbon, 78 00:06:24,490 --> 00:06:29,440 where n is 16 to 20. 79 00:06:29,440 --> 00:06:35,770 And this guy here is called a fatty acid. 80 00:06:40,000 --> 00:06:44,200 And out of the addition of glycerol and the fatty acid-- 81 00:06:44,200 --> 00:06:46,670 I'm going to put a line between the two so that you 82 00:06:46,670 --> 00:06:47,920 can see the difference-- 83 00:06:50,430 --> 00:06:52,340 comes something called a triglyceride. 84 00:07:02,570 --> 00:07:06,200 And I'm going to draw this for just one of the glycerol 85 00:07:06,200 --> 00:07:07,480 carbon atoms. 86 00:07:07,480 --> 00:07:10,840 And then the same thing is true for all the others. 87 00:07:10,840 --> 00:07:15,320 So you'll have CH2 at the end, and then a 88 00:07:15,320 --> 00:07:16,740 condensation reaction. 89 00:07:31,220 --> 00:07:33,950 And we're going to write et cetera here, being casual 90 00:07:33,950 --> 00:07:36,140 about this. 91 00:07:36,140 --> 00:07:39,530 And out of this comes this triglyceride. 92 00:07:39,530 --> 00:07:49,130 This reaction is a condensation reaction. 93 00:07:49,130 --> 00:07:50,380 It eliminates water. 94 00:07:53,750 --> 00:07:55,220 It's a condensation reaction. 95 00:07:58,480 --> 00:08:10,160 And it's also a transesterification, where you 96 00:08:10,160 --> 00:08:17,300 can see the ester bond formed in the triglyceride. 97 00:08:17,300 --> 00:08:20,500 I'm going to notate triglycerides in a slightly 98 00:08:20,500 --> 00:08:22,110 different way. 99 00:08:22,110 --> 00:08:24,170 I'll show you this in a moment. 100 00:08:24,170 --> 00:08:28,260 But let's take a look at a picture here so you can see 101 00:08:28,260 --> 00:08:31,250 what it actually looks like. 102 00:08:31,250 --> 00:08:34,100 Here's glycerol, from your book. 103 00:08:34,100 --> 00:08:36,799 And here is a fatty acid. 104 00:08:36,799 --> 00:08:41,580 And here are the reactive species interacting to give 105 00:08:41,580 --> 00:08:46,760 you a condensation reaction and joining up the glycerol to 106 00:08:46,760 --> 00:08:48,580 the fatty acid. 107 00:08:48,580 --> 00:08:53,290 And the glycerol then serves as a backbone to have these 108 00:08:53,290 --> 00:08:55,470 three chains of fatty acid. 109 00:08:55,470 --> 00:08:57,690 Hence the name triglycerides. 110 00:08:57,690 --> 00:09:00,490 Lipids are not, strictly speaking, polymers. 111 00:09:00,490 --> 00:09:03,440 And so what I said about macromolecules being polymers 112 00:09:03,440 --> 00:09:05,860 really doesn't hold for lipids. 113 00:09:05,860 --> 00:09:07,890 But the other principles do. 114 00:09:11,690 --> 00:09:16,400 One of the things about lipids is that they can be modified. 115 00:09:16,400 --> 00:09:21,720 And they can be modified by replacing one of the fatty 116 00:09:21,720 --> 00:09:25,540 acid chains with something that is polar. 117 00:09:25,540 --> 00:09:30,340 So if you look at this triglyceride, you can see at a 118 00:09:30,340 --> 00:09:33,260 glance that it is really hydrogens and carbons. 119 00:09:33,260 --> 00:09:34,510 It's very non-polar. 120 00:09:34,510 --> 00:09:36,680 There's a couple of oxygens up here. 121 00:09:36,680 --> 00:09:39,840 But there are so few relative to the molecule that really 122 00:09:39,840 --> 00:09:41,950 this is a very non-polar molecule. 123 00:09:41,950 --> 00:09:44,500 But you can change the properties of lipids in an 124 00:09:44,500 --> 00:09:48,410 extraordinary way by replacing one of the fatty acid chains 125 00:09:48,410 --> 00:09:49,860 with something polar. 126 00:09:49,860 --> 00:09:52,415 And that is particularly done in phospholipids. 127 00:10:05,770 --> 00:10:09,110 And we're going to now draw a triglyceride in a different 128 00:10:09,110 --> 00:10:17,690 way, in shorthand, where the glycerol is going to have a 129 00:10:17,690 --> 00:10:24,190 horizontal bar and the fatty acid chains are going to 130 00:10:24,190 --> 00:10:27,070 emanate as vertical lines. 131 00:10:27,070 --> 00:10:33,380 The triglyceride, your classic one, is hydrophobic because it 132 00:10:33,380 --> 00:10:34,630 is non-polar. 133 00:10:39,020 --> 00:10:42,820 But you can also take one of those side chains, or one of 134 00:10:42,820 --> 00:10:47,290 those fatty acid chains, and replace it 135 00:10:47,290 --> 00:10:49,040 with a phosphate group. 136 00:10:49,040 --> 00:11:02,500 So you can replace one fatty acid with a phosphate, which 137 00:11:02,500 --> 00:11:04,070 is highly charged. 138 00:11:04,070 --> 00:11:14,960 And then you get something like this, where the blob is 139 00:11:14,960 --> 00:11:17,070 the phosphate group. 140 00:11:17,070 --> 00:11:21,030 Phospholipids are the things which make cell membranes. 141 00:11:21,030 --> 00:11:26,300 And they make cell membranes because they are on one end 142 00:11:26,300 --> 00:11:29,420 polar, and on the other end they're non-polar. 143 00:11:29,420 --> 00:11:35,040 And so here on the top end, they are polar and 144 00:11:35,040 --> 00:11:36,540 hydrophilic. 145 00:11:36,540 --> 00:11:41,340 And then the bottom part is non-polar. 146 00:11:41,340 --> 00:11:51,820 And this causes them to self-associate so that the 147 00:11:51,820 --> 00:11:54,670 polar groups face water and the non-polar 148 00:11:54,670 --> 00:11:56,410 groups face one another. 149 00:11:56,410 --> 00:12:01,230 And these will spontaneously form a lipid bilayer, the 150 00:12:01,230 --> 00:12:05,070 thing that surrounds all of the cell and all of the 151 00:12:05,070 --> 00:12:06,270 organelles. 152 00:12:06,270 --> 00:12:11,610 So they will go and spontaneously associate into a 153 00:12:11,610 --> 00:12:37,130 bilayered membrane, which we can draw like this, using our 154 00:12:37,130 --> 00:12:39,350 shorthand notation. 155 00:12:39,350 --> 00:12:42,380 And what I've done is to now put the hydrophobic or the 156 00:12:42,380 --> 00:12:44,465 non-polar bits facing one another. 157 00:12:52,780 --> 00:12:59,240 And these polar bits are now interacting with water. 158 00:12:59,240 --> 00:13:00,490 So these are hydrophilic-- 159 00:13:02,850 --> 00:13:04,100 which I'm going to hyphenate. 160 00:13:08,340 --> 00:13:10,810 And they are indeed interacting with water. 161 00:13:10,810 --> 00:13:15,630 Let's look at some pictures to exemplify this. 162 00:13:15,630 --> 00:13:18,830 Here is the chemical structure of a phospholipid. 163 00:13:18,830 --> 00:13:20,790 They're the long-chain fatty acids. 164 00:13:20,790 --> 00:13:22,290 And here's the phosphate group. 165 00:13:22,290 --> 00:13:24,570 This is actually a modified phosphate group. 166 00:13:24,570 --> 00:13:27,380 It's got a choline moiety, which makes 167 00:13:27,380 --> 00:13:30,600 it even more polar. 168 00:13:30,600 --> 00:13:34,200 And here you go with this little bit sticking out. 169 00:13:34,200 --> 00:13:36,890 So you can see the shape of the molecule has changed. 170 00:13:36,890 --> 00:13:40,100 And also its electronegativity has changed. 171 00:13:40,100 --> 00:13:44,900 And here are these molecules that spontaneously form this 172 00:13:44,900 --> 00:13:48,220 lipid bilayer, the phospholipid membrane, with 173 00:13:48,220 --> 00:13:51,780 all the hydrophilic parts sticking out and touching 174 00:13:51,780 --> 00:13:55,480 water on either side and the hydrophobic parts interacting 175 00:13:55,480 --> 00:13:56,470 with one another. 176 00:13:56,470 --> 00:13:58,950 I want to really make a point that this is 177 00:13:58,950 --> 00:14:00,720 not a double membrane. 178 00:14:00,720 --> 00:14:01,890 This is a single membrane. 179 00:14:01,890 --> 00:14:04,900 We talked last time about mitochondria and the nucleus 180 00:14:04,900 --> 00:14:07,170 having double membranes around them. 181 00:14:07,170 --> 00:14:09,060 That would be two of these. 182 00:14:09,060 --> 00:14:12,000 This thing that we've got up here is a single membrane. 183 00:14:12,000 --> 00:14:14,710 This is what all cell membranes and organelle 184 00:14:14,710 --> 00:14:16,530 membranes look like. 185 00:14:16,530 --> 00:14:18,005 That's an important thing to realize. 186 00:14:23,270 --> 00:14:23,486 The last thing I want to mention -- 187 00:14:23,486 --> 00:14:25,150 Actually, the last thing I want to mention about 188 00:14:25,150 --> 00:14:28,230 triglycerides is that there are a couple of different 189 00:14:28,230 --> 00:14:30,470 kinds of triglyceride chains which are 190 00:14:30,470 --> 00:14:32,540 very important medically. 191 00:14:32,540 --> 00:14:34,720 And you've heard of them. 192 00:14:34,720 --> 00:14:45,850 There are saturated fats, where the triglyceride chains 193 00:14:45,850 --> 00:14:51,910 have got all single carbon atoms. 194 00:14:51,910 --> 00:14:56,280 And all of these completely saturated-- 195 00:14:56,280 --> 00:14:58,220 in other words, there are no double bonds. 196 00:15:07,940 --> 00:15:11,000 Triglycerides with these types of chains 197 00:15:11,000 --> 00:15:12,265 tend to pack tightly. 198 00:15:16,010 --> 00:15:20,750 And this gives them the property of chemical stability 199 00:15:20,750 --> 00:15:23,525 and confers on them a high melting point. 200 00:15:27,540 --> 00:15:30,830 So saturated fats are often solid. 201 00:15:30,830 --> 00:15:32,840 And this is bad. 202 00:15:32,840 --> 00:15:35,980 These are bad for you. 203 00:15:35,980 --> 00:15:41,070 In contrast, unsaturated fats are sometimes good for you and 204 00:15:41,070 --> 00:15:42,600 sometimes not. 205 00:15:42,600 --> 00:15:53,020 So unsaturated fats all have, somewhere, a 206 00:15:53,020 --> 00:15:55,880 carbon double bond. 207 00:15:55,880 --> 00:15:59,150 There are two kinds of unsaturated fats. 208 00:15:59,150 --> 00:16:05,520 There are cis-unsaturated fats, where-- 209 00:16:10,369 --> 00:16:14,150 let's just put in some extra bonds here-- 210 00:16:14,150 --> 00:16:20,160 where the other bonds that are available to the carbons are 211 00:16:20,160 --> 00:16:22,800 on the same side of the molecule. 212 00:16:22,800 --> 00:16:25,980 And you remember that there's no free rotation around a 213 00:16:25,980 --> 00:16:27,100 double bond. 214 00:16:27,100 --> 00:16:32,720 So if that molecule looks like that, it is stuck that way. 215 00:16:32,720 --> 00:16:36,670 If it synthesized that way, it's stuck that way. 216 00:16:36,670 --> 00:16:46,420 On the other hand, there are trans-unsaturated fats, where 217 00:16:46,420 --> 00:16:50,050 the additional valencies of carbon are on opposite sides 218 00:16:50,050 --> 00:16:51,850 of the molecule. 219 00:16:51,850 --> 00:16:52,960 Cis fats-- 220 00:16:52,960 --> 00:16:56,050 I'll show you a slide in a moment-- 221 00:16:56,050 --> 00:16:57,550 so these have got double bonds. 222 00:17:02,080 --> 00:17:08,680 The cis fats pack poorly because they are kinked. 223 00:17:08,680 --> 00:17:11,144 And these have got a low melting point. 224 00:17:15,119 --> 00:17:16,369 And these are good for you. 225 00:17:20,109 --> 00:17:24,150 The trans-fats, however, are much more like the saturated 226 00:17:24,150 --> 00:17:30,155 fats, and they pack tightly, et cetera, high melting point. 227 00:17:37,020 --> 00:17:41,170 And they are particularly bad for you. 228 00:17:41,170 --> 00:17:43,900 Trans-fats are very seldom found in nature. 229 00:17:43,900 --> 00:17:49,060 They are found in Twinkies and other gourmet treats. 230 00:17:49,060 --> 00:17:51,250 All right, let's look at some structures 231 00:17:51,250 --> 00:17:52,230 here from your book. 232 00:17:52,230 --> 00:17:56,380 Saturated fats, you can see the chains are all straight, 233 00:17:56,380 --> 00:17:58,430 and they pack very tightly. 234 00:17:58,430 --> 00:18:03,810 Cis-unsaturated fats, here's a bend in the chain, and this 235 00:18:03,810 --> 00:18:07,470 makes the molecules pack loosely. 236 00:18:07,470 --> 00:18:10,970 This is a steric, a spatial, consideration. 237 00:18:10,970 --> 00:18:13,930 And then if you look at trans and cis fats, 238 00:18:13,930 --> 00:18:15,000 here's oleic acid. 239 00:18:15,000 --> 00:18:17,120 It's the same carbon chain. 240 00:18:17,120 --> 00:18:20,690 But trans-oleic acid has a straight chain, 241 00:18:20,690 --> 00:18:22,770 cis-oleic has a bend. 242 00:18:22,770 --> 00:18:25,080 They're both unsaturated fats. 243 00:18:25,080 --> 00:18:31,510 And the question that I am sure you have seen is whether 244 00:18:31,510 --> 00:18:35,270 or not trans fat should be removed from all food, and how 245 00:18:35,270 --> 00:18:38,300 that can be done, and why it is bad for you. 246 00:18:38,300 --> 00:18:41,850 And now it's required that there are ingredients posted 247 00:18:41,850 --> 00:18:45,290 on various food so that you know what you're eating. 248 00:18:45,290 --> 00:18:48,200 And I'm going to tell you a little bit about why trans fat 249 00:18:48,200 --> 00:18:49,410 is bad for you. 250 00:18:49,410 --> 00:18:52,640 But I have to introduce to you another lipid and another 251 00:18:52,640 --> 00:18:55,880 class of lipids in order to do so. 252 00:18:55,880 --> 00:18:59,040 And that's not the only reason that I'm going to introduce 253 00:18:59,040 --> 00:19:00,430 this other class of lipids. 254 00:19:00,430 --> 00:19:05,360 I'm going to do it because it's a very important class. 255 00:19:05,360 --> 00:19:09,150 So a second class of lipids that we should consider beyond 256 00:19:09,150 --> 00:19:11,643 the triglycerides are the steroids. 257 00:19:19,310 --> 00:19:26,070 Steroids share a common ring structure. 258 00:19:26,070 --> 00:19:30,910 They are lipids with a common ring structure. 259 00:19:39,050 --> 00:19:44,410 And I have the slide up so you can look at it even now. 260 00:19:44,410 --> 00:19:46,820 Their precursor is cholesterol. 261 00:19:54,370 --> 00:19:58,420 And cholesterol is, in fact, not bad. 262 00:19:58,420 --> 00:20:01,140 It is an essential lipid. 263 00:20:01,140 --> 00:20:06,000 And it's essential both for formation of the membrane, and 264 00:20:06,000 --> 00:20:14,060 all membranes, and it is also crucial for signaling. 265 00:20:14,060 --> 00:20:18,580 And if an organism develops without cholesterol, it 266 00:20:18,580 --> 00:20:20,650 develops with one eye. 267 00:20:20,650 --> 00:20:25,060 You lack the whole midline that divides you into two more 268 00:20:25,060 --> 00:20:28,610 or less bilaterally symmetric parts. 269 00:20:28,610 --> 00:20:33,140 So cholesterol is a very essential component. 270 00:20:33,140 --> 00:20:38,570 Other things that come from lipids are vitamin D, much in 271 00:20:38,570 --> 00:20:42,450 the news also with regard to preventing inflammation, and 272 00:20:42,450 --> 00:20:43,700 various hormones. 273 00:20:49,040 --> 00:20:52,480 Their structure's on the board -- on the screen. 274 00:20:52,480 --> 00:20:55,640 And you can see, in green, the common ring structure with 275 00:20:55,640 --> 00:21:01,610 various other groups attached, which give these different 276 00:21:01,610 --> 00:21:04,660 steroidal lipids their particular structures. 277 00:21:04,660 --> 00:21:07,850 And we'll come back to the notion of cholesterol and why 278 00:21:07,850 --> 00:21:12,360 it's both essential but-- let me annotate here-- 279 00:21:12,360 --> 00:21:18,340 too much is bad. 280 00:21:18,340 --> 00:21:19,590 All right. 281 00:21:21,400 --> 00:21:26,570 In the news a lot are steroids androgens, a particular class 282 00:21:26,570 --> 00:21:29,560 of artificial androgens are normal steroids. 283 00:21:29,560 --> 00:21:32,200 But there is a class of artificial steroids. 284 00:21:32,200 --> 00:21:36,930 Here's one, tetrahydrogestrinone, which is 285 00:21:36,930 --> 00:21:38,490 used by athletes. 286 00:21:38,490 --> 00:21:42,290 It is mostly undetectable. 287 00:21:42,290 --> 00:21:46,700 The tests for anabolic steroids used by athletes are 288 00:21:46,700 --> 00:21:48,340 actually very high tech. 289 00:21:48,340 --> 00:21:50,830 And this one is very difficult to detect. 290 00:21:50,830 --> 00:21:53,560 And it makes the question of whether particular athletes 291 00:21:53,560 --> 00:21:56,610 have used steroids rather difficult to answer 292 00:21:56,610 --> 00:21:57,860 unequivocally. 293 00:22:02,480 --> 00:22:02,736 Too much cholesterol -- 294 00:22:02,736 --> 00:22:03,850 I should be using the screen. 295 00:22:03,850 --> 00:22:07,000 Too much cholesterol leads to a condition called 296 00:22:07,000 --> 00:22:10,450 atherosclerosis, where cholesterol is deposited in 297 00:22:10,450 --> 00:22:11,850 the arteries. 298 00:22:11,850 --> 00:22:12,900 Here it is. 299 00:22:12,900 --> 00:22:16,100 And this literally physically blocks up the artery, causes 300 00:22:16,100 --> 00:22:19,580 the blood to clot, and leads to heart attacks. 301 00:22:19,580 --> 00:22:22,500 And here's an artery that's OK-- 302 00:22:22,500 --> 00:22:24,340 well, actually it's not quite, there. 303 00:22:24,340 --> 00:22:26,490 You can see it's being injected with contrast, and 304 00:22:26,490 --> 00:22:29,060 there's a little place where it's not OK. 305 00:22:29,060 --> 00:22:32,400 And here's one which is completely occluded by an 306 00:22:32,400 --> 00:22:34,090 atherosclerotic plaque. 307 00:22:34,090 --> 00:22:36,990 What's the deal with cholesterol? 308 00:22:36,990 --> 00:22:41,960 Cholesterol is used for membranes and signalling. 309 00:22:41,960 --> 00:22:45,360 But it also is carried through the body by a component called 310 00:22:45,360 --> 00:22:47,370 low-density lipoprotein. 311 00:22:47,370 --> 00:22:50,910 And this low-density lipoprotein, or LDL, is 312 00:22:50,910 --> 00:22:53,430 deposited in the arteries, where it plugs them and leads 313 00:22:53,430 --> 00:22:55,550 to heart attack. 314 00:22:55,550 --> 00:22:58,510 If cholesterol binds high-density lipoproteins, a 315 00:22:58,510 --> 00:23:01,970 different kind of a transport molecule, then the excess 316 00:23:01,970 --> 00:23:05,400 cholesterol is excreted by the liver, and you're good. 317 00:23:05,400 --> 00:23:06,760 You're well. 318 00:23:06,760 --> 00:23:10,870 Turns out, through complicated reasons, that trans fat and 319 00:23:10,870 --> 00:23:14,960 saturated fat increases the levels of this bad, 320 00:23:14,960 --> 00:23:17,500 low-density lipoprotein and thereby 321 00:23:17,500 --> 00:23:19,140 increases heart attacks. 322 00:23:19,140 --> 00:23:22,750 I should note that most cholesterol is made by you. 323 00:23:22,750 --> 00:23:25,990 80% of your cholesterol is made by you. 324 00:23:25,990 --> 00:23:27,740 20% you get from food. 325 00:23:27,740 --> 00:23:30,780 So eating a low cholesterol diet usually doesn't do much 326 00:23:30,780 --> 00:23:32,150 for cholesterol levels. 327 00:23:32,150 --> 00:23:35,170 You actually have to interfere with synthesis, which is what 328 00:23:35,170 --> 00:23:39,080 the various drugs called statins do. 329 00:23:39,080 --> 00:23:39,390 All right. 330 00:23:39,390 --> 00:23:41,840 So enough about lipids. 331 00:23:41,840 --> 00:23:48,210 Let us move to our third topic today, another fascinating and 332 00:23:48,210 --> 00:23:52,690 important set of macromolecules, the 333 00:23:52,690 --> 00:23:53,940 carbohydrates. 334 00:23:57,060 --> 00:24:01,380 Carbohydrates make up about 25% of the dry 335 00:24:01,380 --> 00:24:02,940 mass of a cell . 336 00:24:08,990 --> 00:24:14,370 They're used as an energy source, as a carbon source to 337 00:24:14,370 --> 00:24:15,620 build other molecules. 338 00:24:19,400 --> 00:24:23,600 And they also encode information, as in your blood 339 00:24:23,600 --> 00:24:29,256 type, which I will try to touch on in a few moments. 340 00:24:29,256 --> 00:24:33,270 Their chemical formula is much simpler and is polymeric, 341 00:24:33,270 --> 00:24:34,520 unlike the lipids. 342 00:24:38,260 --> 00:24:45,670 (CH2O)n, or if you like, more informatively, (H-C-OH)n. 343 00:24:48,540 --> 00:24:52,240 And because of the hydroxyl group, carbohydrates are 344 00:24:52,240 --> 00:24:54,995 pretty much always hydrophilic. 345 00:25:01,090 --> 00:25:05,760 The monomer of carbohydrates is called a monosaccharide. 346 00:25:05,760 --> 00:25:09,460 And there can be polymers that are two 347 00:25:09,460 --> 00:25:12,330 monomers or multiple monomers. 348 00:25:12,330 --> 00:25:14,370 So the monomer-- 349 00:25:14,370 --> 00:25:16,580 and you should know this-- 350 00:25:16,580 --> 00:25:20,300 is called a monosaccharide, where 351 00:25:20,300 --> 00:25:22,590 saccharide sounds like saccharin. 352 00:25:22,590 --> 00:25:23,840 That means sugar. 353 00:25:26,070 --> 00:25:30,850 And there can be dimers, which would be a small polymer, 354 00:25:30,850 --> 00:25:33,800 which would be a disaccharide. 355 00:25:33,800 --> 00:25:38,860 And then you can also get long sugars, which would be 356 00:25:38,860 --> 00:25:40,110 polysaccharides. 357 00:25:43,460 --> 00:25:47,390 A monosaccharide, for example, would be glucose. 358 00:25:47,390 --> 00:25:51,640 A disaccharide, sucrose. 359 00:25:51,640 --> 00:26:00,340 And a polysaccharide, glycogen in animals or 360 00:26:00,340 --> 00:26:05,355 cellulose in plants. 361 00:26:09,450 --> 00:26:10,210 All right. 362 00:26:10,210 --> 00:26:14,520 Let's look at the condensation reaction that is responsible 363 00:26:14,520 --> 00:26:16,390 for making carbohydrates. 364 00:26:16,390 --> 00:26:18,580 It's a simple condensation reaction, at 365 00:26:18,580 --> 00:26:19,540 least on the board. 366 00:26:19,540 --> 00:26:23,090 It requires careful orchestration by the cell, but 367 00:26:23,090 --> 00:26:25,920 on the board it's easy to draw. 368 00:26:25,920 --> 00:26:35,506 One carbohydrate plus another carbohydrate-- 369 00:26:38,620 --> 00:26:40,920 I'm not going to put all the side groups on, but you 370 00:26:40,920 --> 00:26:46,900 understand there are other side groups here or another 371 00:26:46,900 --> 00:26:50,530 carbon there, giving rise to-- 372 00:27:00,690 --> 00:27:02,780 with the release of water. 373 00:27:02,780 --> 00:27:05,650 So here is a condensation reaction. 374 00:27:05,650 --> 00:27:10,770 And this bond that forms in carbohydrates-- 375 00:27:10,770 --> 00:27:15,140 I'm actually going to add the next carbons on here, instead 376 00:27:15,140 --> 00:27:20,100 of X. I apologize for erasing here, but let's put some 377 00:27:20,100 --> 00:27:23,710 carbons here rather than X because that will be clearer. 378 00:27:23,710 --> 00:27:29,340 But the bond between two monomers is called a 379 00:27:29,340 --> 00:27:31,910 glycosidic bond. 380 00:27:31,910 --> 00:27:34,810 And that designates that it is found in carbohydrates. 381 00:27:47,700 --> 00:27:50,260 Carbohydrates can isomerize. 382 00:27:50,260 --> 00:27:53,800 That means the same chemical formula can change its shape, 383 00:27:53,800 --> 00:28:02,620 can change the organization of its atoms, and can isomerize 384 00:28:02,620 --> 00:28:08,015 between the ring and a linear structure. 385 00:28:10,860 --> 00:28:13,910 And carbohydrates can also be modified. 386 00:28:13,910 --> 00:28:17,680 They remain hydrophilic in general, but there are many 387 00:28:17,680 --> 00:28:23,570 modifications which are rather crucial to their function. 388 00:28:23,570 --> 00:28:28,710 They can get, for example, phosphate 389 00:28:28,710 --> 00:28:33,930 groups or amino groups. 390 00:28:40,540 --> 00:28:42,480 And this will change their particular properties. 391 00:28:46,510 --> 00:28:48,600 Let's look at some slides. 392 00:28:48,600 --> 00:28:52,220 And then I want to tell you about a very fascinating and 393 00:28:52,220 --> 00:28:55,070 important example of carbohydrates as an 394 00:28:55,070 --> 00:28:56,500 information source. 395 00:28:56,500 --> 00:29:01,840 So here's glucose as straight chain and glucose as a ring. 396 00:29:01,840 --> 00:29:03,880 If you're not familiar with looking at chemical 397 00:29:03,880 --> 00:29:04,740 structures-- 398 00:29:04,740 --> 00:29:06,930 I keep forgetting that is my usual board. 399 00:29:06,930 --> 00:29:09,210 But let's look at this one because it's brighter. 400 00:29:09,210 --> 00:29:11,280 If you're not familiar with looking at chemical 401 00:29:11,280 --> 00:29:15,350 structures, if you see these dark areas in a molecule, it 402 00:29:15,350 --> 00:29:18,150 means that the molecule is coming out of the board 403 00:29:18,150 --> 00:29:18,900 towards you. 404 00:29:18,900 --> 00:29:19,750 So it gives a bit of 405 00:29:19,750 --> 00:29:22,035 three-dimensionality to that molecule. 406 00:29:25,040 --> 00:29:28,480 And here are the condensation reactions involved in the 407 00:29:28,480 --> 00:29:32,090 formation of maltose, which is a glucose disaccharide. 408 00:29:32,090 --> 00:29:34,800 And here is the glycosidic linkage. 409 00:29:34,800 --> 00:29:39,060 The atoms in carbohydrates get particular numbers. 410 00:29:39,060 --> 00:29:42,410 It is the carbon atoms that get particular numbers. 411 00:29:42,410 --> 00:29:45,270 And next lecture, that is going to become very important 412 00:29:45,270 --> 00:29:47,410 when we talk about nucleic acids. 413 00:29:47,410 --> 00:29:51,030 And here is sucrose, a dimer of glucose and fructose. 414 00:29:56,110 --> 00:30:01,610 Now, depending on the orientation of these bonds 415 00:30:01,610 --> 00:30:05,610 between the saccharides, between the monomers, they may 416 00:30:05,610 --> 00:30:11,620 or may not be able to be broken by the enzymes, by the 417 00:30:11,620 --> 00:30:14,030 chemicals in your body that are involved 418 00:30:14,030 --> 00:30:16,810 in hydrolysis reactions. 419 00:30:16,810 --> 00:30:20,550 So sucroses can be broken down pretty much by everyone. 420 00:30:20,550 --> 00:30:24,350 But lactose, which is the galactose-glucose dimer has 421 00:30:24,350 --> 00:30:29,100 got a glycosidic bond which has a particular shape. 422 00:30:29,100 --> 00:30:33,150 And that particular shape is only recognized by people who 423 00:30:33,150 --> 00:30:35,890 have a molecule called lactase-- 424 00:30:35,890 --> 00:30:38,160 we'll talk about this in a couple of lectures-- 425 00:30:38,160 --> 00:30:40,820 which is able to break this chemical bond here. 426 00:30:40,820 --> 00:30:43,440 And if you're lactose intolerant, the reason you get 427 00:30:43,440 --> 00:30:46,400 stomach ache and so on is because you get accumulation 428 00:30:46,400 --> 00:30:49,260 of this disaccharide, and it has side effects on your 429 00:30:49,260 --> 00:30:51,475 digestive system. 430 00:30:51,475 --> 00:30:52,600 All right. 431 00:30:52,600 --> 00:30:57,930 So I want to tell you now about a really fascinating 432 00:30:57,930 --> 00:31:05,670 example of information as encoded by carbohydrates. 433 00:31:05,670 --> 00:31:07,780 We will have much more to say about 434 00:31:07,780 --> 00:31:09,860 carbohydrates as we go along. 435 00:31:09,860 --> 00:31:12,510 But I'm going to tell you about information-- 436 00:31:12,510 --> 00:31:14,510 particularly here, because we won't talk about 437 00:31:14,510 --> 00:31:16,600 it very much more. 438 00:31:16,600 --> 00:31:20,150 One example of carbohydrates giving information is in your 439 00:31:20,150 --> 00:31:21,670 blood type. 440 00:31:21,670 --> 00:31:28,130 So for blood type, there are specific 441 00:31:28,130 --> 00:31:36,580 carbohydrates for each. 442 00:31:36,580 --> 00:31:50,270 But there is the same core set of molecules, which is then 443 00:31:50,270 --> 00:31:58,510 modified to give you the different blood groups, to 444 00:31:58,510 --> 00:31:59,780 four blood groups. 445 00:32:06,100 --> 00:32:09,490 This is a representation of the four blood groups. 446 00:32:09,490 --> 00:32:11,610 They are called O, A, B, and AB. 447 00:32:11,610 --> 00:32:13,890 And you probably know which one you are. 448 00:32:13,890 --> 00:32:16,890 I am A. 449 00:32:16,890 --> 00:32:19,850 One of those blood groups is really valuable. 450 00:32:19,850 --> 00:32:23,320 It's called O. And it's valuable because anyone could 451 00:32:23,320 --> 00:32:25,910 receive this blood in a transfusion. 452 00:32:25,910 --> 00:32:34,830 And anyone can because it's kind of your basic blood type. 453 00:32:34,830 --> 00:32:39,190 It contains an H group, which is the basic sugar information 454 00:32:39,190 --> 00:32:40,680 on blood cells. 455 00:32:40,680 --> 00:32:43,800 And all of the other blood groups also contains this 456 00:32:43,800 --> 00:32:48,060 basic information, but they contain other sugars as well, 457 00:32:48,060 --> 00:32:50,890 here indicated by purple. 458 00:32:50,890 --> 00:32:54,730 The key to these different sugars is indicated below. 459 00:32:54,730 --> 00:33:00,540 But O can be given to any kind of person because you do not 460 00:33:00,540 --> 00:33:04,520 have antibodies against this particular H group. 461 00:33:04,520 --> 00:33:08,090 Because everyone's got it. 462 00:33:08,090 --> 00:33:12,440 So O is the only blood group where, when you put it into 463 00:33:12,440 --> 00:33:14,740 anyone, there are not antibodies-- 464 00:33:14,740 --> 00:33:16,690 which you'll learn about later in the course-- 465 00:33:16,690 --> 00:33:19,830 that will then attack the blood cells and cause massive 466 00:33:19,830 --> 00:33:22,300 blood clots and deaths. 467 00:33:22,300 --> 00:33:32,540 When people donate blood, 3/4 of it is not O. After a time, 468 00:33:32,540 --> 00:33:35,690 blood is thrown away from blood banks because it's not 469 00:33:35,690 --> 00:33:37,540 usable forever. 470 00:33:37,540 --> 00:33:41,430 And a lot of this type, A, B and AB blood, is thrown away. 471 00:33:41,430 --> 00:33:45,020 And so investigators have been asking for a long time whether 472 00:33:45,020 --> 00:33:49,270 they couldn't remove these extra sugars from AB, B, and 473 00:33:49,270 --> 00:33:53,190 A, and turn those bloods into type O, which would then be 474 00:33:53,190 --> 00:33:54,955 useful for everyone. 475 00:33:54,955 --> 00:33:58,100 It turns out that's kind of difficult to do. 476 00:33:58,100 --> 00:34:01,080 But a few years ago, a group did come up with 477 00:34:01,080 --> 00:34:02,980 what may be a solution. 478 00:34:02,980 --> 00:34:04,970 It still hasn't been proved, even though this 479 00:34:04,970 --> 00:34:05,810 was a few years ago. 480 00:34:05,810 --> 00:34:07,430 It takes a long time. 481 00:34:07,430 --> 00:34:09,889 Here's a different representation of the sugars 482 00:34:09,889 --> 00:34:11,389 on blood types. 483 00:34:11,389 --> 00:34:15,710 Here's group A and group B. And there are enzymes-- 484 00:34:15,710 --> 00:34:17,159 there you see, office hours. 485 00:34:17,159 --> 00:34:17,770 I'm not kidding. 486 00:34:17,770 --> 00:34:20,679 It's on my calendar. 487 00:34:20,679 --> 00:34:22,340 All right. 488 00:34:22,340 --> 00:34:25,699 There are substances, enzymes, we'll talk about which can 489 00:34:25,699 --> 00:34:30,080 actually remove some of these sugars off groups A and B and 490 00:34:30,080 --> 00:34:33,949 convert them into group O. These substances, these 491 00:34:33,949 --> 00:34:36,469 enzymes, were isolated by Liu et al. 492 00:34:36,469 --> 00:34:38,030 When you see this at the bottom-- 493 00:34:38,030 --> 00:34:39,400 Here's a piece of education. 494 00:34:39,400 --> 00:34:42,239 Often I will show you something, and in the bottom 495 00:34:42,239 --> 00:34:45,590 right-hand corner it will say "Liu et al" or "Jones et al" 496 00:34:45,590 --> 00:34:46,520 and a date. 497 00:34:46,520 --> 00:34:48,800 That refers to a publication. 498 00:34:48,800 --> 00:34:52,880 This group was able to convert group type A and type B into a 499 00:34:52,880 --> 00:34:56,900 type O. And they are now working on a machine which can 500 00:34:56,900 --> 00:35:02,600 convert type A, AB, and B blood into type O. 501 00:35:02,600 --> 00:35:03,850 And we'll stop there.