1 00:00:00 --> 00:00:04 I am a professor in the Biology Department at MIT. 2 00:00:04 --> 00:00:09 And I will be co-teaching this course with Penny Chisholm who is a 3 00:00:09 --> 00:00:14 professor in the Department of Civil and Environmental Engineering, 4 00:00:14 --> 00:00:19 as well as a professor in the Biology Department. 5 00:00:19 --> 00:00:24 As well, Penny was recently featured in the journal Nature. 6 00:00:24 --> 00:00:29 She is a very well-known oceanographer who has become 7 00:00:29 --> 00:00:34 deservedly famous for discovering a very small bacterium that's capable 8 00:00:34 --> 00:00:39 of carrying out photosynthesis. For many years oceanographers used 9 00:00:39 --> 00:00:43 filters whose holes were big enough that this bacterium went through. 10 00:00:43 --> 00:00:47 And so when they were doing their studies of the ocean and how the 11 00:00:47 --> 00:00:51 biomass that was there and all the fluxes and so on, 12 00:00:51 --> 00:00:55 they didn't know this organism existed which can form up to 50% of 13 00:00:55 --> 00:01:00 the biomass in parts of the ocean. So Penny is really a wonderful 14 00:01:00 --> 00:01:05 lecturer, a wonderful person, and she'll be teaching the component 15 00:01:05 --> 00:01:10 of 7.014 which deals with ecology and the environment. 16 00:01:10 --> 00:01:15 And this is a section of 7. 14 that makes it different from the 17 00:01:15 --> 00:01:20 other two versions, 7.012 and 7.013. So for me 18 00:01:20 --> 00:01:25 personally this is an absolutely wonderful and exciting opportunity 19 00:01:25 --> 00:01:30 to be able to teach this Introductory Biology course. 20 00:01:30 --> 00:01:34 For some of you I know that biology is going to either be a major part 21 00:01:34 --> 00:01:38 of your career or quite possibly, even if you're in engineering or 22 00:01:38 --> 00:01:43 something else, you will find yourselves working 23 00:01:43 --> 00:01:47 with a biological system. You can see that happening all over 24 00:01:47 --> 00:01:52 campus these days that more and more engineering departments are finding 25 00:01:52 --> 00:01:56 that they're working on problems that come from biology or have a 26 00:01:56 --> 00:02:01 biological component. I'm sure there are at least a few 27 00:02:01 --> 00:02:05 of you here who are only here because it's a required course and 28 00:02:05 --> 00:02:10 you might well wish you were somewhere else. 29 00:02:10 --> 00:02:14 However, I will do my best to try to communicate to you why you need to 30 00:02:14 --> 00:02:19 know some biology, too. I think most of you know you 31 00:02:19 --> 00:02:23 can hardly pick up a newspaper these days without running into something 32 00:02:23 --> 00:02:28 that demands a knowledge of biology, something about stem cells, 33 00:02:28 --> 00:02:33 something about cloning humans, something about a new drug, lots of 34 00:02:33 --> 00:02:37 things having to do with biological affects on the environment 35 00:02:37 --> 00:02:42 and so on. You're also going to be confronted 36 00:02:42 --> 00:02:46 with decisions about your health, about the health of your loved ones 37 00:02:46 --> 00:02:51 concerning cancer, concerning whether a child might 38 00:02:51 --> 00:02:55 have birth defects, all sort of issues that will affect 39 00:02:55 --> 00:03:00 your personal lives that demand an understanding of biology. 40 00:03:00 --> 00:03:04 So I feel with some passion that whether you think you're going to 41 00:03:04 --> 00:03:08 need biology in your professional career or not, 42 00:03:08 --> 00:03:13 everyone in this institution needs some understanding of biology to 43 00:03:13 --> 00:03:17 just live their ordinary lives. I also think as MIT students you're 44 00:03:17 --> 00:03:21 going to be looked at, as you go through your lives, 45 00:03:21 --> 00:03:26 as people who are knowledgeable about science and engineering. 46 00:03:26 --> 00:03:30 And you'll be asked questions that go far beyond your immediate 47 00:03:30 --> 00:03:35 area of expertise. And again I think that's another 48 00:03:35 --> 00:03:39 reason for needing to know some of biology. Anyway, 49 00:03:39 --> 00:03:44 it's an absolutely wonderful time to teach biology because things have 50 00:03:44 --> 00:03:48 just been exploding over the last two or three decades and things are 51 00:03:48 --> 00:03:53 moving faster than ever. And another wonderful thing about 52 00:03:53 --> 00:03:57 teaching biology is that MIT is an absolutely marvelous place 53 00:03:57 --> 00:04:02 to teach it. Just to sort of drive this home, 54 00:04:02 --> 00:04:07 in the Biology Department alone there are four Nobel laureates who 55 00:04:07 --> 00:04:12 got honored for critical discoveries in biology. Gobin Khorana who is 56 00:04:12 --> 00:04:17 just down the hall from me synthesized the first gene. 57 00:04:17 --> 00:04:22 It was an extraordinary feat of synthesis of organic chemistry 58 00:04:22 --> 00:04:27 synthesizing DNA. When I was an undergrad I was a 59 00:04:27 --> 00:04:32 chemistry major but I had to take an introductory biology course. 60 00:04:32 --> 00:04:36 And at that point the DNA wasn't mentioned in the high school course. 61 00:04:36 --> 00:04:40 So the first time that I heard about DNA was in my introductory 62 00:04:40 --> 00:04:44 biology course. And that determined by career 63 00:04:44 --> 00:04:48 direction. I thought that was such an interesting molecule that I 64 00:04:48 --> 00:04:52 wanted to work on it and I talked myself into one of the labs in 65 00:04:52 --> 00:04:56 Ottawa, Canada where I grew up that was trying to synthesize DNA, 66 00:04:56 --> 00:05:00 synthesize pieces of the gene. And, as it turned out later, 67 00:05:00 --> 00:05:05 competing unsuccessfully with my now colleague Gobin Khorana. 68 00:05:05 --> 00:05:09 Susumu Tonegawa got a Nobel prize for discovering the amazing 69 00:05:09 --> 00:05:14 molecular operations that underlie the diversity of the immune system. 70 00:05:14 --> 00:05:18 Your immune system has the capacity to recognize viruses and bacteria, 71 00:05:18 --> 00:05:23 all sorts of different pathogens, including molecules. 72 00:05:23 --> 00:05:27 It can recognize molecules that haven't even ever been synthesized 73 00:05:27 --> 00:05:32 in the history of life. And we'll talk towards the end of 74 00:05:32 --> 00:05:36 the course about the way that happens. And you'll see why Susumu 75 00:05:36 --> 00:05:40 got his Nobel prize. Phil Sharp got his for discovering 76 00:05:40 --> 00:05:45 RNA splicing completely unanticipated component of the very 77 00:05:45 --> 00:05:49 heart of molecular biology. And then Bob Horvitz who was of 78 00:05:49 --> 00:05:54 pure mind when he started at MIT at the same time and our labs were side 79 00:05:54 --> 00:05:58 by side for many years, got his Nobel prize in 2002 for 80 00:05:58 --> 00:06:02 discovering a phenomenon, the general term is “programmed” 81 00:06:02 --> 00:06:07 cell death. And it plays all sorts of important 82 00:06:07 --> 00:06:12 roles in biology from sculpting the shapes of organs and tissues. 83 00:06:12 --> 00:06:17 We initially have webs when we're developing between our fingers, 84 00:06:17 --> 00:06:22 and those go away because of the programmed cell death that the cells 85 00:06:22 --> 00:06:27 that were making the web disappear. And another role of that is prevent 86 00:06:27 --> 00:06:32 cancer. That if cells sense that something is very messed up they 87 00:06:32 --> 00:06:37 have a sort of suicide program that would make them destroy themselves. 88 00:06:37 --> 00:06:41 And if that doesn't happen those cells could go on and become more 89 00:06:41 --> 00:06:46 and more abnormal and eventually turn into an invasive cancer. 90 00:06:46 --> 00:06:50 Anyway, there's a picture of Bob when the institute was celebrating 91 00:06:50 --> 00:06:55 his Nobel prize. He was getting a congratulatory 92 00:06:55 --> 00:07:00 kiss from Martha Constantine-Paton, also a professor in the Biology 93 00:07:00 --> 00:07:05 Department who happens to be Bob's wife. 94 00:07:05 --> 00:07:09 Most of you know that the human genome has now been sequenced. 95 00:07:09 --> 00:07:14 That was one of the huge undertakings and most important 96 00:07:14 --> 00:07:18 undertakings in modern biology over the last while. 97 00:07:18 --> 00:07:23 It was an incredible feat. Each cell has, as most of you know, 98 00:07:23 --> 00:07:27 46 chromosomes. And that's a total of about two meters of DNA 99 00:07:27 --> 00:07:32 in every human cell. And that two meters of DNA is 100 00:07:32 --> 00:07:37 composed of about 3 million DNA base pairs, these letters A, 101 00:07:37 --> 00:07:42 T, G and C that we'll be talking about as we go through the course. 102 00:07:42 --> 00:07:47 So to sequence the genome you had to work out the sequence of the 103 00:07:47 --> 00:07:52 exact run of these A, G, T and Cs along the backbone for 3 104 00:07:52 --> 00:07:57 billion base pairs. And somewhere that genome encodes 105 00:07:57 --> 00:08:02 somewhere between 20,000 and 30,000 genes. 106 00:08:02 --> 00:08:06 And we'll be talking about the proteins that are encoded by most of 107 00:08:06 --> 00:08:11 those genes and their important roles as we go on in the course. 108 00:08:11 --> 00:08:15 What some of you may not know is the key role that MIT played in this. 109 00:08:15 --> 00:08:20 About a third of the genome was sequenced at the Whitehead MIT 110 00:08:20 --> 00:08:24 Genome Center. And here are some of the robots 111 00:08:24 --> 00:08:29 that were used to sequence that DNA. 112 00:08:29 --> 00:08:34 And that sequencing effort was led by Eric Lander whose name some of 113 00:08:34 --> 00:08:39 you may recognize because he teaches the fall version of 7. 114 00:08:39 --> 00:08:44 12 along with Bob Weinberg. So here are just a few examples of 115 00:08:44 --> 00:08:49 why I think it's important for you to understand biology regardless of 116 00:08:49 --> 00:08:54 whether you're going to go on and use it professionally. 117 00:08:54 --> 00:08:59 Most of you know one of the biggest challenges we face on this planet is 118 00:08:59 --> 00:09:04 this AIDS epidemic. It's caused by a certain kind of 119 00:09:04 --> 00:09:10 virus called HIV-1 that gets into particular cells of your immune 120 00:09:10 --> 00:09:16 system that normally defends us against infection and destroys those. 121 00:09:16 --> 00:09:22 And then people die from infections by other organisms that normally you 122 00:09:22 --> 00:09:28 can fight off. It's a huge problem with vast 123 00:09:28 --> 00:09:33 societal and economic implications. And it's one that we're still, 124 00:09:33 --> 00:09:37 as a mankind still trying to deal with and grapple with. 125 00:09:37 --> 00:09:41 Here's another example. Just a couple of years ago there 126 00:09:41 --> 00:09:45 was the scar of anthrax. It's a bacterium that's very 127 00:09:45 --> 00:09:50 pathogenic and kills its host fairly easily. It does it by making 128 00:09:50 --> 00:09:54 particular toxins. The details shown here don't matter, 129 00:09:54 --> 00:09:58 but just reminding you that this is something that was in the front 130 00:09:58 --> 00:10:03 pages of the paper just a little while ago. 131 00:10:03 --> 00:10:07 A couple of years ago, when I was teaching this, 132 00:10:07 --> 00:10:11 we had the scare of the SARS virus that went all the way during the 133 00:10:11 --> 00:10:15 course when I was teaching it from the initial discovery of the virus 134 00:10:15 --> 00:10:19 to the actual sequencing of the genome which had happened by later 135 00:10:19 --> 00:10:23 on in this course. Smallpox was a disease we thought 136 00:10:23 --> 00:10:27 that we eliminated, but now it's come back as a 137 00:10:27 --> 00:10:32 bioterrorism treat and there is increased study of smallpox. 138 00:10:32 --> 00:10:36 It's something we have to worry about again. Here's another example. 139 00:10:36 --> 00:10:40 This is a picture showing the start of a transgenic animal. 140 00:10:40 --> 00:10:44 We'll talk about how this process goes later in the course. 141 00:10:44 --> 00:10:48 And it's related also to this whole issue of cloning, 142 00:10:48 --> 00:10:52 using the sense of the word such as in trying to clone a human or clone 143 00:10:52 --> 00:10:56 an animal to make a genetically identical copy. 144 00:10:56 --> 00:11:00 So you'll see there are a couple of different uses of the word cloning 145 00:11:00 --> 00:11:05 as we go through the course. There's a lot of fuss in the news 146 00:11:05 --> 00:11:09 and the newspapers about genetically modified food, 147 00:11:09 --> 00:11:13 and people have different positions on it. Here's a case where I think 148 00:11:13 --> 00:11:18 the benefit of a genetically modified food could hardly be argued 149 00:11:18 --> 00:11:22 with. About two-thirds of the world's population uses rice as 150 00:11:22 --> 00:11:26 their primary source of food. One of the problems with rice is 151 00:11:26 --> 00:11:31 that it doesn't make beta-carotene. And beta carotene is what our bodies 152 00:11:31 --> 00:11:35 take and use to make vitamin A. And if you have a vitamin A 153 00:11:35 --> 00:11:40 deficiency people are prone to infection. They have immune 154 00:11:40 --> 00:11:45 deficiencies in their immune system and blindness. 155 00:11:45 --> 00:11:49 And this deficiency of vitamin A caused by eating rice afflicts about 156 00:11:49 --> 00:11:54 400 million people worldwide. Well, rice is only two chemical 157 00:11:54 --> 00:11:59 steps away from being able to make beta carotene. 158 00:11:59 --> 00:12:03 This is a genetically modified version of rice that has those two 159 00:12:03 --> 00:12:07 extra steps inserted in it. And you can see it's golden because 160 00:12:07 --> 00:12:11 it's making beta carotene. If people were to eat that form of 161 00:12:11 --> 00:12:15 rice then they wouldn't have this problem with vitamin A deficiency. 162 00:12:15 --> 00:12:19 Penny Chisholm in her part of the course will be considering things 163 00:12:19 --> 00:12:23 that are more global level. Here's a picture of our planet, 164 00:12:23 --> 00:12:27 and there are issues that you know about there. This is the carbon 165 00:12:27 --> 00:12:32 dioxide levels in the atmosphere rising. 166 00:12:32 --> 00:12:37 And that's a real phenomenon. This shows from 1960 to 1995. 167 00:12:37 --> 00:12:42 This is associated with a global warming that again is undeniable 168 00:12:42 --> 00:12:48 that it's happening. You'll see stuff in the papers. 169 00:12:48 --> 00:12:53 And these gases, particularly carbon dioxide and methane, 170 00:12:53 --> 00:12:59 they're known as greenhouse gases are playing a role in that. 171 00:12:59 --> 00:12:54 And probably mankind is playing a role in the production of those 172 00:12:54 --> 00:12:50 gases and, hence, in global warming. 173 00:12:50 --> 00:12:45 And Penny will talk to you a little more about that. 174 00:12:45 --> 00:12:41 Right here at MIT Mario Molina in EAPS discovered the ozone hole and 175 00:12:41 --> 00:12:36 got a Nobel prize for that. Ozone is important because it 176 00:12:36 --> 00:12:32 absorbs UV, a critical component of ultraviolet radiation that would 177 00:12:32 --> 00:12:28 damage our cells if we were exposed to it. 178 00:12:28 --> 00:12:39 And because of the emission of fluorocarbons in the environment 179 00:12:39 --> 00:12:50 this large hole developed over Antarctic. If that had spread, 180 00:12:50 --> 00:13:01 it would have been a real disaster. And that seems to be, the efforts 181 00:13:01 --> 00:13:12 to cut down the release of fluorocarbons seem to be helping 182 00:13:12 --> 00:13:23 with that. But, again, Penny will have more to say. 183 00:13:23 --> 00:13:34 Those of you who've lived around here for a little bit probably know 184 00:13:34 --> 00:13:45 that the fishing industry just locally has had a very hard time. 185 00:13:45 --> 00:13:56 There is a fishing boat just up in Gloucester, just up the coast less 186 00:13:56 --> 00:14:04 than an hour from here. And part of the problems, 187 00:14:04 --> 00:14:08 again, are caused by mismanagement of the resources where the fish have 188 00:14:08 --> 00:14:12 been, stocks have been over-fished so some of the fisheries have come 189 00:14:12 --> 00:14:17 to the point of collapse or near. Places such as the Grand Banks off 190 00:14:17 --> 00:14:21 of Newfoundland there has been a collapse, and it's not at all clear 191 00:14:21 --> 00:14:25 that it can be reversed and whether they'll be cod in large quantities 192 00:14:25 --> 00:14:31 every again there. OK. So there a variety of ways that we 193 00:14:31 --> 00:14:39 can study biology. And I think I'm going to begin by 194 00:14:39 --> 00:14:46 outlining how we do that. Biology is an experimental science 195 00:14:46 --> 00:14:54 and it's one of the really important themes that we'll run through 196 00:14:54 --> 00:15:00 in this course. You cannot study biology by just 197 00:15:00 --> 00:15:04 sitting down with a pen and paper in a room and thinking. 198 00:15:04 --> 00:15:08 You have to get out and find out what's there. You need to make 199 00:15:08 --> 00:15:12 observations. You need to try experiments. You need to formulate 200 00:15:12 --> 00:15:16 hypotheses and test them and either modify your hypothesis or reject it 201 00:15:16 --> 00:15:20 and so on. But it's a continual cycle of experimentation and making 202 00:15:20 --> 00:15:24 hypotheses and testing. It's the Scientific Method at work. 203 00:15:24 --> 00:15:29 But you can carry that out at different levels. 204 00:15:29 --> 00:15:39 The very highest level would be the biosphere. Here's one example. 205 00:15:39 --> 00:15:49 That's earth. It's here. There are many, many species of life that 206 00:15:49 --> 00:16:00 are on there. There are many more than a million. 207 00:16:00 --> 00:16:04 And the estimates of how many there are range from, 208 00:16:04 --> 00:16:09 in total, 10 to the 20 million estimated. And one of the big 209 00:16:09 --> 00:16:13 worries right at the moment is that as rain forests are being depleted, 210 00:16:13 --> 00:16:18 parts of the world that are a rich source of biological diversity, 211 00:16:18 --> 00:16:23 as those are disappearing we're losing diversity at quite a rate. 212 00:16:23 --> 00:16:27 Just a couple of years ago I had a chance to fly over 213 00:16:27 --> 00:16:32 a part of Brazil. And it was just scary to see from 214 00:16:32 --> 00:16:37 the plane how the rain forest was just being cut down. 215 00:16:37 --> 00:16:42 And you could just see how fast some of the rain forest was 216 00:16:42 --> 00:16:48 disappearing, and with it many different types of species that only 217 00:16:48 --> 00:16:53 can live there. One can look instead, 218 00:16:53 --> 00:16:58 going down a level, at an ecosystem which is a particular 219 00:16:58 --> 00:17:06 environment -- 220 00:17:06 --> 00:17:10 -- and the species of life found in it. And just to give you a couple 221 00:17:10 --> 00:17:14 of examples of that, it could be a salt marsh as shown 222 00:17:14 --> 00:17:18 here. Or here's an interesting environment that Penny Chisholm will 223 00:17:18 --> 00:17:22 tell you more about. This is a black smoker. 224 00:17:22 --> 00:17:26 There's a vent several miles deep in the Pacific Ocean. 225 00:17:26 --> 00:17:30 The water temperature that's gushing out of here is around 360 226 00:17:30 --> 00:17:35 degree centigrade. And there's a particular community 227 00:17:35 --> 00:17:40 of life that's able to grow around these deep vents. 228 00:17:40 --> 00:17:46 And Penny will tell you more about that. Then going down yet another 229 00:17:46 --> 00:17:56 level you can come to a population. 230 00:17:56 --> 00:18:07 And this is interacting -- 231 00:18:07 --> 00:18:11 -- or interbreeding organisms. An example might be the fiddler 232 00:18:11 --> 00:18:16 crabs in a salt marsh. Or here we see an interesting 233 00:18:16 --> 00:18:20 population. These are tube worms that are up to a meter or more in 234 00:18:20 --> 00:18:25 length that you find down at these black smokers. 235 00:18:25 --> 00:18:34 If we move down yet another level -- 236 00:18:34 --> 00:18:39 -- we come to organisms. Organisms have three important 237 00:18:39 --> 00:18:45 sorts of characteristics that we'll talk quite a bit about in this 238 00:18:45 --> 00:18:51 course. They carry out metabolism which is the sum of all the 239 00:18:51 --> 00:18:57 different chemical reactions necessary for life. 240 00:18:57 --> 00:19:07 They undergo regulated growth -- 241 00:19:07 --> 00:19:12 -- and they reproduce. And the sort of fundamental unit of 242 00:19:12 --> 00:19:17 life that we will talk about over and over again in this course is 243 00:19:17 --> 00:19:22 known as a cell. And life comes in two kinds of 244 00:19:22 --> 00:19:29 species. There is unicellular life where the 245 00:19:29 --> 00:19:37 organism is just a single cell and multicellular forms of life that are 246 00:19:37 --> 00:19:45 made of many different types of cells. What's a cell? 247 00:19:45 --> 00:19:53 One of the secrets to life. It's a little tiny bit of the 248 00:19:53 --> 00:20:02 universe that's surrounded by a boundary. 249 00:20:02 --> 00:20:07 And it's given the special name of a membrane. It's selective, 250 00:20:07 --> 00:20:12 not very permeable to most things. And cells are able to put little 251 00:20:12 --> 00:20:17 importers and exporters and things that control the passage of things 252 00:20:17 --> 00:20:22 across the membrane by isolating the inside of a cell from all the rest 253 00:20:22 --> 00:20:27 of the universe. That is one of the principles that 254 00:20:27 --> 00:20:32 makes life possible. We have a couple of examples of 255 00:20:32 --> 00:20:38 organisms here. Here are some clams that grow down 256 00:20:38 --> 00:20:43 at those black smokers, and they can get pretty large. 257 00:20:43 --> 00:20:49 And, as I say, Penny will talk a bit more about this. 258 00:20:49 --> 00:20:54 And we have this really amazing diversity of life forms that we find 259 00:20:54 --> 00:21:00 on this planet. However, if we think about this 260 00:21:00 --> 00:21:06 division into unicellular and multicellular organisms. 261 00:21:06 --> 00:21:10 Unicellular organisms include things that you're familiar with. 262 00:21:10 --> 00:21:15 They're bacteria. There is a picture of just E. 263 00:21:15 --> 00:21:20 coli cells. And we'll be talking about E. coli quite a bit as a model 264 00:21:20 --> 00:21:25 organism as we go through the course. By studying E. 265 00:21:25 --> 00:21:30 coli, scientists have learned many important things that apply 266 00:21:30 --> 00:21:35 to all of life. Another kind of important 267 00:21:35 --> 00:21:41 single-celled organism, unicellular organism is yeast. 268 00:21:41 --> 00:21:46 Those are pictures of yeast saccharomyces that are used in 269 00:21:46 --> 00:21:52 baking bread or in brewing beer or making wine. And another one you're 270 00:21:52 --> 00:21:58 all familiar with are algae which are single-celled organisms that are 271 00:21:58 --> 00:22:04 able to carry out photosynthesis. And we'll be talking about that. 272 00:22:04 --> 00:22:11 If we think of an example of a multicellular organism then we see 273 00:22:11 --> 00:22:18 there are different levels at which we can think about this. 274 00:22:18 --> 00:22:25 We could take, for example, a picture of me, just an 275 00:22:25 --> 00:22:32 anatomically correct diagram here, that I'm made up, as you are, of 276 00:22:32 --> 00:22:39 about ten to the fourteenth human cells. 277 00:22:39 --> 00:22:43 We all started out as a fertilized egg, which is a single cell. 278 00:22:43 --> 00:22:48 And by the time we're grown up, where we have about ten to the 279 00:22:48 --> 00:22:53 fourteenth human cells. Just a tremendous amount of cell 280 00:22:53 --> 00:22:58 growth that had to happen and specialization. 281 00:22:58 --> 00:23:02 The other thing you may not appreciate is that we have an 282 00:23:02 --> 00:23:07 ecosystem inside us in our gastrointestinal tract. 283 00:23:07 --> 00:23:11 This part, the intestine having the highest concentration of 284 00:23:11 --> 00:23:16 microorganisms. But there are about ten to the 285 00:23:16 --> 00:23:20 fourteenth bacteria also inside of our gut. So we're actually almost 286 00:23:20 --> 00:23:25 the same number of human cells and bacterial cells. 287 00:23:25 --> 00:23:29 And if we don't have those bacteria then our digestive systems 288 00:23:29 --> 00:23:35 don't work well. So if we go down from a whole 289 00:23:35 --> 00:23:41 organism, a whole multicellular organism, a level, 290 00:23:41 --> 00:23:47 then we come to an organ. An example of that might be an eye. 291 00:23:47 --> 00:23:53 And I think we have a diagram of an eye which is made up of different 292 00:23:53 --> 00:24:00 parts. If we go down another level we come to a tissue. 293 00:24:00 --> 00:24:07 Which is now you can begin to see that tissue are made up of groups of 294 00:24:07 --> 00:24:14 specialized cells. An example might be the retina of 295 00:24:14 --> 00:24:21 an eye. And if we continue to go downwards we'll get to single cells. 296 00:24:21 --> 00:24:28 And at this point we're at the same level of the tail as when we're 297 00:24:28 --> 00:24:35 talking about a unicellular organism. 298 00:24:35 --> 00:24:46 If we continue down then -- 299 00:24:46 --> 00:24:54 -- we can get to organelles. These are involved in energy 300 00:24:54 --> 00:25:04 production, energy management. 301 00:25:04 --> 00:25:10 And mitochondrion and chloroplasts are the two principle examples of 302 00:25:10 --> 00:25:16 organelles that we'll talk about. And if we go down yet another level 303 00:25:16 --> 00:25:22 of organization we get to molecules. And part of the reason that biology 304 00:25:22 --> 00:25:28 has flourished so well over the last few decades at MIT is there has been 305 00:25:28 --> 00:25:34 a real emphasis on looking at things at a cellular and molecular level. 306 00:25:34 --> 00:25:38 So you're going to be hearing a lot about cells and a lot about 307 00:25:38 --> 00:25:42 molecules as we go through this course. Here's an example of 308 00:25:42 --> 00:25:46 rhodopsin. That's a protein. We'll be talking about what 309 00:25:46 --> 00:25:50 proteins are, but it's a very important class of molecule in 310 00:25:50 --> 00:25:54 nature. In this case, proteins involved in sensing light 311 00:25:54 --> 00:25:59 and play an important part in your vision. 312 00:25:59 --> 00:26:02 Here is another protein. You cannot really tell what it's 313 00:26:02 --> 00:26:06 doing by just looking at it, but in this case this is one of the 314 00:26:06 --> 00:26:10 lethal factors that is made by anthrax. It's one of the proteins 315 00:26:10 --> 00:26:14 that anthrax makes that's capable of killing you if you get infected with 316 00:26:14 --> 00:26:18 it. Here's another molecule we'll talk about in great detail. 317 00:26:18 --> 00:26:22 This is DNA. You probably all know it's a double helix, 318 00:26:22 --> 00:26:26 two strands of DNA that are held together by forces we'll 319 00:26:26 --> 00:26:30 be discussing. It's an absolutely beautiful 320 00:26:30 --> 00:26:36 molecule. It's fascinated me through all of my life. 321 00:26:36 --> 00:26:41 And we'll be talking quite a bit about that as the course goes on. 322 00:26:41 --> 00:26:47 OK. So if we're thinking about cells there are two important kinds 323 00:26:47 --> 00:26:53 of cells that one finds on this planet. 324 00:26:53 --> 00:27:01 Prokaryotic cells. 325 00:27:01 --> 00:27:07 Prokaryotic organisms and eukaryotic organisms. 326 00:27:07 --> 00:27:14 They each are made of cells that are distinguishable from each other. 327 00:27:14 --> 00:27:20 I've indicated that a cell is a little bit of the universe that's 328 00:27:20 --> 00:27:27 surrounded by a boundary or a membrane. But inside there, 329 00:27:27 --> 00:27:34 inside of this is the DNA which functions as the genetic material. 330 00:27:34 --> 00:27:40 It's the blueprint for everything that that cell is going to make and 331 00:27:40 --> 00:27:47 be able to do. Ultimately everything is encoded 332 00:27:47 --> 00:27:53 there. And in a prokaryotic cell the DNA is free within this membrane. 333 00:27:53 --> 00:28:00 The eukaryotic cell also has a membrane. 334 00:28:00 --> 00:28:08 But the DNA inside is inside another membrane compartment known as the 335 00:28:08 --> 00:28:16 nucleus. And this is the DNA. These prokaryotic cells tend to be 336 00:28:16 --> 00:28:24 of the order of a kilometer in length. And eukaryotic cells are 337 00:28:24 --> 00:28:32 usually larger, can be ten to a hundred kilometers. 338 00:28:32 --> 00:28:36 There's quite a bit of variation, but that gives you at least some 339 00:28:36 --> 00:28:40 sense of the range. Now, I've for years, 340 00:28:40 --> 00:28:45 when I did a diagram like this, I wanted to somehow be able to show 341 00:28:45 --> 00:28:49 you that these cells were impressive than just what's on the board. 342 00:28:49 --> 00:28:54 So here are a couple of pictures to try and do that. 343 00:28:54 --> 00:28:58 This shows a picture of E. coli swimming along. And the way 344 00:28:58 --> 00:29:03 this image is being taken lets you see what are called flagella but 345 00:29:03 --> 00:29:07 which are basically the propellers that E. coli have that let it swim 346 00:29:07 --> 00:29:12 through the water. These are long structures made of 347 00:29:12 --> 00:29:17 proteins that are several times the body length of the bacterium. 348 00:29:17 --> 00:29:22 And there's a molecular motor imbedded in the bacterium that 349 00:29:22 --> 00:29:27 whirls it around at about somewhere between 10,000 and 100, 350 00:29:27 --> 00:29:32 00 RPM. And that's what drives the bacteria forward. 351 00:29:32 --> 00:29:36 So that was a prokaryotic cell. Here's a paramecium. This is a 352 00:29:36 --> 00:29:41 single-celled eukaryotic organism. And, as you can see here, it's 353 00:29:41 --> 00:29:46 capable of movement as well. In this case it has cilia along the 354 00:29:46 --> 00:29:51 outside that allow it to move. Here's an interesting one. I don't 355 00:29:51 --> 00:29:56 know if any of you can guess what these were. These were cells from 356 00:29:56 --> 00:30:01 the skin of a mouse. They're on an Auger surface. 357 00:30:01 --> 00:30:05 And, as you can see, they too can move. There are a 358 00:30:05 --> 00:30:10 couple of things that are important about this. I got this slide from 359 00:30:10 --> 00:30:14 Linda Griffith who is in the Biological Engineering Department. 360 00:30:14 --> 00:30:19 At the time I got it from her I think it was in Chemical Engineering 361 00:30:19 --> 00:30:23 several years ago. And what was important about this, 362 00:30:23 --> 00:30:28 apart from it being a very nice little movie showing you a mammalian 363 00:30:28 --> 00:30:32 cell moving around, was that I saw Linda show this 364 00:30:32 --> 00:30:37 during one of her research seminars. 365 00:30:37 --> 00:30:41 So here is an engineer at MIT who was showing this picture as part of 366 00:30:41 --> 00:30:45 her research talk. And I think those of you who are 367 00:30:45 --> 00:30:49 going onto engineering, you may be surprised at the extent 368 00:30:49 --> 00:30:53 to which you need to know about biology as you go through your 369 00:30:53 --> 00:31:01 professional careers. 370 00:31:01 --> 00:31:08 OK. So one of the great discoveries that has happened over the last few 371 00:31:08 --> 00:31:15 years that came out of our ability to look at DNA and RNA was the 372 00:31:15 --> 00:31:22 discovery that the forms of life that are prokaryotic actually split 373 00:31:22 --> 00:31:30 into two distinct Kingdoms that are very, very different. 374 00:31:30 --> 00:31:34 The archaea and the bacteria. And just to give you a sense of the 375 00:31:34 --> 00:31:39 diversity of life, I'll just mention a couple of these. 376 00:31:39 --> 00:31:44 These archaea look like bacteria but they are diverged from the 377 00:31:44 --> 00:31:49 bacteria as they are from the eukaryotes. So there were sort of 378 00:31:49 --> 00:31:54 three really major Kingdoms of Life. And the archaea, many of them can 379 00:31:54 --> 00:32:00 live in specialized environments. For example, sulfolobus can live at 380 00:32:00 --> 00:32:07 about 90 degrees centigrade and a pH of somewhere between 1 and 2. 381 00:32:07 --> 00:32:14 So if you see something like a hot springs, there are organisms such as 382 00:32:14 --> 00:32:21 this that are able to grow in that environment. Or there are halophyes, 383 00:32:21 --> 00:32:28 salt-loving archaea that can grow, for example, in formula sodium 384 00:32:28 --> 00:32:34 chloride. And if you've, 385 00:32:34 --> 00:32:38 for example, ever flown into San Francisco airport coming up from the 386 00:32:38 --> 00:32:42 south over San Jose, you've seen things that look sort of 387 00:32:42 --> 00:32:46 like these pictures where seawater is being evaporated down to collect 388 00:32:46 --> 00:32:51 the salt. And you'll see they're colored, and the reason they're 389 00:32:51 --> 00:32:55 colored is that these halobacteria are photobacteria that are able to 390 00:32:55 --> 00:32:59 use light as an energy source. And they make pigments that absorb 391 00:32:59 --> 00:33:04 the light, and that's why these salt areas get colored. 392 00:33:04 --> 00:33:11 A third example would be methanogens. These are organisms that produce 393 00:33:11 --> 00:33:18 methane. If you've walked into a lake and stepped on the bottom and 394 00:33:18 --> 00:33:25 seen little bubbles come up, those are little bubbles of methane. 395 00:33:25 --> 00:33:32 Or another place where you find methanogens are inside of cows. 396 00:33:32 --> 00:33:37 Now, some of you may not know that the cow is more or less a walking 397 00:33:37 --> 00:33:42 anaerobic fermentor here. If we have an anatomically correct 398 00:33:42 --> 00:33:47 picture of a cow. The inside of the cow, 399 00:33:47 --> 00:33:52 there's a large chamber known as the rumen where there's no oxygen, 400 00:33:52 --> 00:33:57 and there's a culture of microorganisms there that 401 00:33:57 --> 00:34:02 include methanogens. And it's this combination of 402 00:34:02 --> 00:34:07 microorganisms that enables cows to each grass that we cannot manage to 403 00:34:07 --> 00:34:12 get energy from. And as a byproduct of this 404 00:34:12 --> 00:34:17 specialized type of metabolism produces methane. 405 00:34:17 --> 00:34:23 And a cow burps something of the order of 400 liters a day of methane. 406 00:34:23 --> 00:34:28 OK. So one last thing then just to kind of pull this all together is 407 00:34:28 --> 00:34:33 that these organelles that I mentioned, which are also membrane 408 00:34:33 --> 00:34:38 compartments that are found in eukaryotic cells, are 409 00:34:38 --> 00:35:50 the mitochondria -- 410 00:35:50 --> 00:35:31 -- or chloroplast. There's pretty strong evidence at 411 00:35:31 --> 00:35:13 this point that these arose from bacteria that were things that 412 00:35:13 --> 00:35:07 you're more familiar with. Things like E. 413 00:35:07 --> 00:35:15 coli or streptococcus that causes strep throat or the lactic acid 414 00:35:15 --> 00:35:23 bacteria that causes the milk to turn into yogurt which some of you 415 00:35:23 --> 00:35:29 probably had for lunch today. That these organelles, 416 00:35:29 --> 00:35:33 the mitochondria and the chloroplast were derived from particular type of 417 00:35:33 --> 00:35:37 bacteria that probably first got transiently associated with 418 00:35:37 --> 00:35:41 developing eukaryotic cells sometime back in evolution, 419 00:35:41 --> 00:35:45 and eventually became captured and became a permanent part of the 420 00:35:45 --> 00:35:49 eukaryotic cell. The mitochondrion is thought to 421 00:35:49 --> 00:35:53 have derived from something that looks like today's present day 422 00:35:53 --> 00:35:57 rizobia, which we'll talk about, that form an intracellular infection 423 00:35:57 --> 00:36:02 of plants, or rickettsia which is chronic intracellular pathogen. 424 00:36:02 --> 00:36:05 The mitochondrion look as though they came from something related to 425 00:36:05 --> 00:36:09 that. The chloroplasts look as though they came from a bacterium 426 00:36:09 --> 00:36:13 that was able to carry on photosynthesis which we'll also be 427 00:36:13 --> 00:36:17 talking about. I want to close by giving you just 428 00:36:17 --> 00:36:21 a quick little snapshot of evolution because I'm hoping this will maybe 429 00:36:21 --> 00:36:25 make some of the things that we talk about in this course clearer. 430 00:36:25 --> 00:36:34 So what we're going to do is we're going to look back from 4. 431 00:36:34 --> 00:36:44 billion years ago when the earth was just forming -- 432 00:36:44 --> 00:36:57 -- to now. I'm just going to try 433 00:36:57 --> 00:37:03 and give you a few key sort of landmarks as we go along. 434 00:37:03 --> 00:37:09 So about 4.5 billion years ago there was methane, carbon dioxide, 435 00:37:09 --> 00:37:16 ammonium, hydrogen gas, nitrogen gas, water, but importantly no oxygen at 436 00:37:16 --> 00:37:22 that point. There was a lot of debate as to how life initially came. 437 00:37:22 --> 00:37:29 One of the prevalent theories at this point is there's something 438 00:37:29 --> 00:37:35 called an RNA world. This is just a hypothesis in which 439 00:37:35 --> 00:37:40 it's thought that perhaps the molecule RNA, which we'll talk about, 440 00:37:40 --> 00:37:45 played role as both something that was able to catalyze chemical 441 00:37:45 --> 00:37:51 reactions and therefore did things actively and also stored information. 442 00:37:51 --> 00:37:56 But, in any case, the best guess is that the first 443 00:37:56 --> 00:38:01 life that was about 3. billion years ago, somewhere in 444 00:38:01 --> 00:38:06 that vicinity. It was something that probably 445 00:38:06 --> 00:38:10 resembled most closely a present-day bacterium, a single-celled organism, 446 00:38:10 --> 00:38:14 something like that. Now, initially when life got started it's thought 447 00:38:14 --> 00:38:18 that there were a lot of organic chemicals that had been made as a 448 00:38:18 --> 00:38:22 consequence of lightening strikes and all sorts of chemistry that had 449 00:38:22 --> 00:38:26 happened so there was sort of a soup of some kind, some molecules 450 00:38:26 --> 00:38:31 that could be used. So probably these first organisms 451 00:38:31 --> 00:38:35 where able to basically use some preformed nutrients. 452 00:38:35 --> 00:38:40 And then as the soup began to get depleted by using it they had to 453 00:38:40 --> 00:38:44 learn to synthesize, at least develop systems that would 454 00:38:44 --> 00:38:49 synthesize these building blocks. And they also had to begin to worry 455 00:38:49 --> 00:38:54 about what to use as energy. And so somewhere in here, something 456 00:38:54 --> 00:38:58 that I'll call, in a silly way, photosynthesis 457 00:38:58 --> 00:39:03 released number one. But this was a system that enabled 458 00:39:03 --> 00:39:08 the organism to capture energy from sunlight so that it wasn't now 459 00:39:08 --> 00:39:14 dependent on getting energy by eating some preformed ingredient. 460 00:39:14 --> 00:39:19 It was then able to take carbon dioxide and make it into forms that 461 00:39:19 --> 00:39:24 were useful, of carbon that were useful for life, 462 00:39:24 --> 00:39:30 and it produced molecules such as sulfur as a waste product. 463 00:39:30 --> 00:39:36 There was a bit later in evolution, somewhere in here, something we 464 00:39:36 --> 00:39:43 might think of as photosynthesis release two. This was an improved 465 00:39:43 --> 00:39:49 version of photosynthesis. It captured more energy, worked 466 00:39:49 --> 00:39:56 better, but it developed, it had a waste product which was 467 00:39:56 --> 00:40:02 oxygen. Well, oxygen hadn't been in our 468 00:40:02 --> 00:40:06 atmosphere. And the first thing that sort of happened was that the 469 00:40:06 --> 00:40:10 world started to rust. All the iron, a lot of the iron 470 00:40:10 --> 00:40:14 started to interact with the oxygen. And Penny will tell you that at the 471 00:40:14 --> 00:40:19 base of the sea there are huge beds of iron oxide that came from this 472 00:40:19 --> 00:40:23 slow rusting of the earth. And so it took many, many years 473 00:40:23 --> 00:40:27 before oxygen levels started to rise. As you know it's about 20% of our 474 00:40:27 --> 00:40:32 atmosphere now. Even at this stage it was only a few 475 00:40:32 --> 00:40:37 percent of our, made up a few percent of our 476 00:40:37 --> 00:40:43 atmosphere, even by here in evolution. The first eukaryotic 477 00:40:43 --> 00:40:48 cell is thought to have appeared somewhere here. 478 00:40:48 --> 00:40:53 Again, it was likely a single-celled organism like some of 479 00:40:53 --> 00:40:59 those pictures I showed you. And evolution continued to go. 480 00:40:59 --> 00:41:04 Somewhere around a billion years ago sex was evolved which enabled 481 00:41:04 --> 00:41:09 eukaryotic organisms to exchange genetic material, 482 00:41:09 --> 00:41:15 and therefore evolve at a fast rate than they could previously. 483 00:41:15 --> 00:41:19 The Cambrian Period was about a 0. billion to 0.6 billion years ago. 484 00:41:19 --> 00:41:24 And there was a veritable explosion of life forms. 485 00:41:24 --> 00:41:28 And you can still see in the fossil records how much diversity was 486 00:41:28 --> 00:41:33 generated at that point, some of which went on to become life 487 00:41:33 --> 00:41:38 forms and other which probably were more evolutionary dead ends. 488 00:41:38 --> 00:41:46 Finally we get to the dinosaurs that were about 245 to 65 million years 489 00:41:46 --> 00:41:55 ago which would place them somewhere here on this timeline. 490 00:41:55 --> 00:42:04 So in honor of this course, I've commissioned a full scale model 491 00:42:04 --> 00:42:13 of anatomically correct [NOISE OBSCURES]. 492 00:42:13 --> 00:42:18 So we'll put our dinosaur here, if I can get him to stay put for a 493 00:42:18 --> 00:42:23 minute. All right. And at this point in evolution 494 00:42:23 --> 00:42:28 things started to get interesting. So somewhere about here, 4 million 495 00:42:28 --> 00:42:34 years ago we've got the first evidence of hominoids. 496 00:42:34 --> 00:42:39 Maybe 20,000 years ago we found the cave paintings in France. 497 00:42:39 --> 00:42:45 And then there was the Roman Empire and Columbus discovered America. 498 00:42:45 --> 00:42:51 And you were born and the Red Sox won the World Series and the 499 00:42:51 --> 00:42:57 Patriots have just won the Super Bowl. And we are now here at the 500 00:42:57 --> 00:43:03 peak of evolution which is, as you all know, the MIT student. 501 00:43:03 --> 00:43:06 So we'll put our MIT student here, who I can probably not get to stay 502 00:43:06 --> 00:43:10 put because you can never get MIT students to stay anywhere. 503 00:43:10 --> 00:43:14 But, in any case, this is sort of a silly demonstration. 504 00:43:14 --> 00:43:18 But there is a very profound reason why I'm doing it. 505 00:43:18 --> 00:43:22 And I must say I don't think I'd ever fully appreciated it until I 506 00:43:22 --> 00:43:26 actually thought of doing this demo for the class. 507 00:43:26 --> 00:43:30 But what I think you can see is that evolution, 508 00:43:30 --> 00:43:34 for the most part, happened at the single cell level. 509 00:43:34 --> 00:43:38 Many people tended to think evolution, that was about dinosaurs 510 00:43:38 --> 00:43:42 and all that stuff. We can say that dinosaurs are, 511 00:43:42 --> 00:43:47 practically now, most of evolution occurred at the level of single 512 00:43:47 --> 00:43:51 cells, and that all this amazing diversity we see around us was very 513 00:43:51 --> 00:43:56 recent embellishments in evolution. So that means when you study 514 00:43:56 --> 00:44:00 biology at the cellular and molecular level you find tremendous 515 00:44:00 --> 00:44:04 commonalities. If you look inside a sulfolobus 516 00:44:04 --> 00:44:08 growing in hot spring, if you look inside an E. 517 00:44:08 --> 00:44:12 coli, if you look inside a yeast and you look inside one of our cells you 518 00:44:12 --> 00:44:16 find that, to a huge extent, many, many of the cellular 519 00:44:16 --> 00:44:20 components are common. They arose similarly in evolution 520 00:44:20 --> 00:44:24 that they're shared by all forms of life. Of course, 521 00:44:24 --> 00:44:28 there are some things that developed later and are different. 522 00:44:28 --> 00:44:32 But that's one of the reasons that you can learn so much by studying 523 00:44:32 --> 00:44:36 biology at the cellular molecular level and why we'll emphasize it a 524 00:44:36 --> 00:44:41 fair bit in this course. The other thing that I'd like to 525 00:44:41 --> 00:44:45 make out of this, a theme that you'll hear along is 526 00:44:45 --> 00:44:50 that organisms modify their environment. You can see that in 527 00:44:50 --> 00:44:54 the case of oxygen back when the earth formed. There was no oxygen 528 00:44:54 --> 00:44:59 in our atmosphere. Now we have a lot of it. 529 00:44:59 --> 00:45:03 The reason it's there is because it was generated by organisms carrying 530 00:45:03 --> 00:45:08 out photosynthesis and generating oxygen as a waste product. 531 00:45:08 --> 00:45:13 And that was an absolutely critical thing to enable creatures such as 532 00:45:13 --> 00:45:18 ourselves, which are dependent on oxygen for us just to be alive, 533 00:45:18 --> 00:45:23 if we hadn't had this change in environment things like us could 534 00:45:23 --> 00:45:28 have, organisms like us couldn't have evolved. 535 00:45:28 --> 00:45:32 So, anyway, I hope that will give you a little sort of snapshot of 536 00:45:32 --> 00:45:37 evolution and will help guide your understanding of this course. 537 00:45:37 --> 00:45:40 We'll see you at the next lecture.