WEBVTT 00:00:00.000 --> 00:00:04.000 I am a professor in the Biology Department at MIT. 00:00:04.000 --> 00:00:09.000 And I will be co-teaching this course with Penny Chisholm who is a 00:00:09.000 --> 00:00:14.000 professor in the Department of Civil and Environmental Engineering, 00:00:14.000 --> 00:00:19.000 as well as a professor in the Biology Department. 00:00:19.000 --> 00:00:24.000 As well, Penny was recently featured in the journal Nature. 00:00:24.000 --> 00:00:29.000 She is a very well-known oceanographer who has become 00:00:29.000 --> 00:00:34.000 deservedly famous for discovering a very small bacterium that's capable 00:00:34.000 --> 00:00:39.000 of carrying out photosynthesis. For many years oceanographers used 00:00:39.000 --> 00:00:43.000 filters whose holes were big enough that this bacterium went through. 00:00:43.000 --> 00:00:47.000 And so when they were doing their studies of the ocean and how the 00:00:47.000 --> 00:00:51.000 biomass that was there and all the fluxes and so on, 00:00:51.000 --> 00:00:55.000 they didn't know this organism existed which can form up to 50% of 00:00:55.000 --> 00:01:00.000 the biomass in parts of the ocean. So Penny is really a wonderful 00:01:00.000 --> 00:01:05.000 lecturer, a wonderful person, and she'll be teaching the component 00:01:05.000 --> 00:01:10.000 of 7.014 which deals with ecology and the environment. 00:01:10.000 --> 00:01:15.000 And this is a section of 7. 14 that makes it different from the 00:01:15.000 --> 00:01:20.000 other two versions, 7.012 and 7.013. So for me 00:01:20.000 --> 00:01:25.000 personally this is an absolutely wonderful and exciting opportunity 00:01:25.000 --> 00:01:30.000 to be able to teach this Introductory Biology course. 00:01:30.000 --> 00:01:34.000 For some of you I know that biology is going to either be a major part 00:01:34.000 --> 00:01:38.000 of your career or quite possibly, even if you're in engineering or 00:01:38.000 --> 00:01:43.000 something else, you will find yourselves working 00:01:43.000 --> 00:01:47.000 with a biological system. You can see that happening all over 00:01:47.000 --> 00:01:52.000 campus these days that more and more engineering departments are finding 00:01:52.000 --> 00:01:56.000 that they're working on problems that come from biology or have a 00:01:56.000 --> 00:02:01.000 biological component. I'm sure there are at least a few 00:02:01.000 --> 00:02:05.000 of you here who are only here because it's a required course and 00:02:05.000 --> 00:02:10.000 you might well wish you were somewhere else. 00:02:10.000 --> 00:02:14.000 However, I will do my best to try to communicate to you why you need to 00:02:14.000 --> 00:02:19.000 know some biology, too. I think most of you know you 00:02:19.000 --> 00:02:23.000 can hardly pick up a newspaper these days without running into something 00:02:23.000 --> 00:02:28.000 that demands a knowledge of biology, something about stem cells, 00:02:28.000 --> 00:02:33.000 something about cloning humans, something about a new drug, lots of 00:02:33.000 --> 00:02:37.000 things having to do with biological affects on the environment 00:02:37.000 --> 00:02:42.000 and so on. You're also going to be confronted 00:02:42.000 --> 00:02:46.000 with decisions about your health, about the health of your loved ones 00:02:46.000 --> 00:02:51.000 concerning cancer, concerning whether a child might 00:02:51.000 --> 00:02:55.000 have birth defects, all sort of issues that will affect 00:02:55.000 --> 00:03:00.000 your personal lives that demand an understanding of biology. 00:03:00.000 --> 00:03:04.000 So I feel with some passion that whether you think you're going to 00:03:04.000 --> 00:03:08.000 need biology in your professional career or not, 00:03:08.000 --> 00:03:13.000 everyone in this institution needs some understanding of biology to 00:03:13.000 --> 00:03:17.000 just live their ordinary lives. I also think as MIT students you're 00:03:17.000 --> 00:03:21.000 going to be looked at, as you go through your lives, 00:03:21.000 --> 00:03:26.000 as people who are knowledgeable about science and engineering. 00:03:26.000 --> 00:03:30.000 And you'll be asked questions that go far beyond your immediate 00:03:30.000 --> 00:03:35.000 area of expertise. And again I think that's another 00:03:35.000 --> 00:03:39.000 reason for needing to know some of biology. Anyway, 00:03:39.000 --> 00:03:44.000 it's an absolutely wonderful time to teach biology because things have 00:03:44.000 --> 00:03:48.000 just been exploding over the last two or three decades and things are 00:03:48.000 --> 00:03:53.000 moving faster than ever. And another wonderful thing about 00:03:53.000 --> 00:03:57.000 teaching biology is that MIT is an absolutely marvelous place 00:03:57.000 --> 00:04:02.000 to teach it. Just to sort of drive this home, 00:04:02.000 --> 00:04:07.000 in the Biology Department alone there are four Nobel laureates who 00:04:07.000 --> 00:04:12.000 got honored for critical discoveries in biology. Gobin Khorana who is 00:04:12.000 --> 00:04:17.000 just down the hall from me synthesized the first gene. 00:04:17.000 --> 00:04:22.000 It was an extraordinary feat of synthesis of organic chemistry 00:04:22.000 --> 00:04:27.000 synthesizing DNA. When I was an undergrad I was a 00:04:27.000 --> 00:04:32.000 chemistry major but I had to take an introductory biology course. 00:04:32.000 --> 00:04:36.000 And at that point the DNA wasn't mentioned in the high school course. 00:04:36.000 --> 00:04:40.000 So the first time that I heard about DNA was in my introductory 00:04:40.000 --> 00:04:44.000 biology course. And that determined by career 00:04:44.000 --> 00:04:48.000 direction. I thought that was such an interesting molecule that I 00:04:48.000 --> 00:04:52.000 wanted to work on it and I talked myself into one of the labs in 00:04:52.000 --> 00:04:56.000 Ottawa, Canada where I grew up that was trying to synthesize DNA, 00:04:56.000 --> 00:05:00.000 synthesize pieces of the gene. And, as it turned out later, 00:05:00.000 --> 00:05:05.000 competing unsuccessfully with my now colleague Gobin Khorana. 00:05:05.000 --> 00:05:09.000 Susumu Tonegawa got a Nobel prize for discovering the amazing 00:05:09.000 --> 00:05:14.000 molecular operations that underlie the diversity of the immune system. 00:05:14.000 --> 00:05:18.000 Your immune system has the capacity to recognize viruses and bacteria, 00:05:18.000 --> 00:05:23.000 all sorts of different pathogens, including molecules. 00:05:23.000 --> 00:05:27.000 It can recognize molecules that haven't even ever been synthesized 00:05:27.000 --> 00:05:32.000 in the history of life. And we'll talk towards the end of 00:05:32.000 --> 00:05:36.000 the course about the way that happens. And you'll see why Susumu 00:05:36.000 --> 00:05:40.000 got his Nobel prize. Phil Sharp got his for discovering 00:05:40.000 --> 00:05:45.000 RNA splicing completely unanticipated component of the very 00:05:45.000 --> 00:05:49.000 heart of molecular biology. And then Bob Horvitz who was of 00:05:49.000 --> 00:05:54.000 pure mind when he started at MIT at the same time and our labs were side 00:05:54.000 --> 00:05:58.000 by side for many years, got his Nobel prize in 2002 for 00:05:58.000 --> 00:06:02.000 discovering a phenomenon, the general term is ìprogrammedî 00:06:02.000 --> 00:06:07.000 cell death. And it plays all sorts of important 00:06:07.000 --> 00:06:12.000 roles in biology from sculpting the shapes of organs and tissues. 00:06:12.000 --> 00:06:17.000 We initially have webs when we're developing between our fingers, 00:06:17.000 --> 00:06:22.000 and those go away because of the programmed cell death that the cells 00:06:22.000 --> 00:06:27.000 that were making the web disappear. And another role of that is prevent 00:06:27.000 --> 00:06:32.000 cancer. That if cells sense that something is very messed up they 00:06:32.000 --> 00:06:37.000 have a sort of suicide program that would make them destroy themselves. 00:06:37.000 --> 00:06:41.000 And if that doesn't happen those cells could go on and become more 00:06:41.000 --> 00:06:46.000 and more abnormal and eventually turn into an invasive cancer. 00:06:46.000 --> 00:06:50.000 Anyway, there's a picture of Bob when the institute was celebrating 00:06:50.000 --> 00:06:55.000 his Nobel prize. He was getting a congratulatory 00:06:55.000 --> 00:07:00.000 kiss from Martha Constantine-Paton, also a professor in the Biology 00:07:00.000 --> 00:07:05.000 Department who happens to be Bob's wife. 00:07:05.000 --> 00:07:09.000 Most of you know that the human genome has now been sequenced. 00:07:09.000 --> 00:07:14.000 That was one of the huge undertakings and most important 00:07:14.000 --> 00:07:18.000 undertakings in modern biology over the last while. 00:07:18.000 --> 00:07:23.000 It was an incredible feat. Each cell has, as most of you know, 00:07:23.000 --> 00:07:27.000 46 chromosomes. And that's a total of about two meters of DNA 00:07:27.000 --> 00:07:32.000 in every human cell. And that two meters of DNA is 00:07:32.000 --> 00:07:37.000 composed of about 3 million DNA base pairs, these letters A, 00:07:37.000 --> 00:07:42.000 T, G and C that we'll be talking about as we go through the course. 00:07:42.000 --> 00:07:47.000 So to sequence the genome you had to work out the sequence of the 00:07:47.000 --> 00:07:52.000 exact run of these A, G, T and Cs along the backbone for 3 00:07:52.000 --> 00:07:57.000 billion base pairs. And somewhere that genome encodes 00:07:57.000 --> 00:08:02.000 somewhere between 20,000 and 30,000 genes. 00:08:02.000 --> 00:08:06.000 And we'll be talking about the proteins that are encoded by most of 00:08:06.000 --> 00:08:11.000 those genes and their important roles as we go on in the course. 00:08:11.000 --> 00:08:15.000 What some of you may not know is the key role that MIT played in this. 00:08:15.000 --> 00:08:20.000 About a third of the genome was sequenced at the Whitehead MIT 00:08:20.000 --> 00:08:24.000 Genome Center. And here are some of the robots 00:08:24.000 --> 00:08:29.000 that were used to sequence that DNA. 00:08:29.000 --> 00:08:34.000 And that sequencing effort was led by Eric Lander whose name some of 00:08:34.000 --> 00:08:39.000 you may recognize because he teaches the fall version of 7. 00:08:39.000 --> 00:08:44.000 12 along with Bob Weinberg. So here are just a few examples of 00:08:44.000 --> 00:08:49.000 why I think it's important for you to understand biology regardless of 00:08:49.000 --> 00:08:54.000 whether you're going to go on and use it professionally. 00:08:54.000 --> 00:08:59.000 Most of you know one of the biggest challenges we face on this planet is 00:08:59.000 --> 00:09:04.000 this AIDS epidemic. It's caused by a certain kind of 00:09:04.000 --> 00:09:10.000 virus called HIV-1 that gets into particular cells of your immune 00:09:10.000 --> 00:09:16.000 system that normally defends us against infection and destroys those. 00:09:16.000 --> 00:09:22.000 And then people die from infections by other organisms that normally you 00:09:22.000 --> 00:09:28.000 can fight off. It's a huge problem with vast 00:09:28.000 --> 00:09:33.000 societal and economic implications. And it's one that we're still, 00:09:33.000 --> 00:09:37.000 as a mankind still trying to deal with and grapple with. 00:09:37.000 --> 00:09:41.000 Here's another example. Just a couple of years ago there 00:09:41.000 --> 00:09:45.000 was the scar of anthrax. It's a bacterium that's very 00:09:45.000 --> 00:09:50.000 pathogenic and kills its host fairly easily. It does it by making 00:09:50.000 --> 00:09:54.000 particular toxins. The details shown here don't matter, 00:09:54.000 --> 00:09:58.000 but just reminding you that this is something that was in the front 00:09:58.000 --> 00:10:03.000 pages of the paper just a little while ago. 00:10:03.000 --> 00:10:07.000 A couple of years ago, when I was teaching this, 00:10:07.000 --> 00:10:11.000 we had the scare of the SARS virus that went all the way during the 00:10:11.000 --> 00:10:15.000 course when I was teaching it from the initial discovery of the virus 00:10:15.000 --> 00:10:19.000 to the actual sequencing of the genome which had happened by later 00:10:19.000 --> 00:10:23.000 on in this course. Smallpox was a disease we thought 00:10:23.000 --> 00:10:27.000 that we eliminated, but now it's come back as a 00:10:27.000 --> 00:10:32.000 bioterrorism treat and there is increased study of smallpox. 00:10:32.000 --> 00:10:36.000 It's something we have to worry about again. Here's another example. 00:10:36.000 --> 00:10:40.000 This is a picture showing the start of a transgenic animal. 00:10:40.000 --> 00:10:44.000 We'll talk about how this process goes later in the course. 00:10:44.000 --> 00:10:48.000 And it's related also to this whole issue of cloning, 00:10:48.000 --> 00:10:52.000 using the sense of the word such as in trying to clone a human or clone 00:10:52.000 --> 00:10:56.000 an animal to make a genetically identical copy. 00:10:56.000 --> 00:11:00.000 So you'll see there are a couple of different uses of the word cloning 00:11:00.000 --> 00:11:05.000 as we go through the course. There's a lot of fuss in the news 00:11:05.000 --> 00:11:09.000 and the newspapers about genetically modified food, 00:11:09.000 --> 00:11:13.000 and people have different positions on it. Here's a case where I think 00:11:13.000 --> 00:11:18.000 the benefit of a genetically modified food could hardly be argued 00:11:18.000 --> 00:11:22.000 with. About two-thirds of the world's population uses rice as 00:11:22.000 --> 00:11:26.000 their primary source of food. One of the problems with rice is 00:11:26.000 --> 00:11:31.000 that it doesn't make beta-carotene. And beta carotene is what our bodies 00:11:31.000 --> 00:11:35.000 take and use to make vitamin A. And if you have a vitamin A 00:11:35.000 --> 00:11:40.000 deficiency people are prone to infection. They have immune 00:11:40.000 --> 00:11:45.000 deficiencies in their immune system and blindness. 00:11:45.000 --> 00:11:49.000 And this deficiency of vitamin A caused by eating rice afflicts about 00:11:49.000 --> 00:11:54.000 400 million people worldwide. Well, rice is only two chemical 00:11:54.000 --> 00:11:59.000 steps away from being able to make beta carotene. 00:11:59.000 --> 00:12:03.000 This is a genetically modified version of rice that has those two 00:12:03.000 --> 00:12:07.000 extra steps inserted in it. And you can see it's golden because 00:12:07.000 --> 00:12:11.000 it's making beta carotene. If people were to eat that form of 00:12:11.000 --> 00:12:15.000 rice then they wouldn't have this problem with vitamin A deficiency. 00:12:15.000 --> 00:12:19.000 Penny Chisholm in her part of the course will be considering things 00:12:19.000 --> 00:12:23.000 that are more global level. Here's a picture of our planet, 00:12:23.000 --> 00:12:27.000 and there are issues that you know about there. This is the carbon 00:12:27.000 --> 00:12:32.000 dioxide levels in the atmosphere rising. 00:12:32.000 --> 00:12:37.000 And that's a real phenomenon. This shows from 1960 to 1995. damage our cells if we were exposed to it. 00:12:37.000 --> 00:12:42.000 This is associated with a global warming that again is undeniable 00:12:42.000 --> 00:12:48.000 that it's happening. You'll see stuff in the papers. 00:12:48.000 --> 00:12:53.000 And these gases, particularly carbon dioxide and methane, 00:12:53.000 --> 00:12:59.000 they're known as greenhouse gases are playing a role in that. 00:12:59.000 --> 00:12:54.000 And probably mankind is playing a role in the production of those 00:12:54.000 --> 00:12:50.000 gases and, hence, in global warming. 00:12:50.000 --> 00:12:45.000 And Penny will talk to you a little more about that. it would have been a real disaster. And that seems to be, the efforts 00:12:45.000 --> 00:12:41.000 Right here at MIT Mario Molina in EAPS discovered the ozone hole and 00:12:41.000 --> 00:12:36.000 got a Nobel prize for that. Ozone is important because it 00:12:36.000 --> 00:12:32.000 absorbs UV, a critical component of ultraviolet radiation that would 00:12:28.000 --> 00:12:39.000 And because of the emission of fluorocarbons in the environment 00:12:39.000 --> 00:12:50.000 this large hole developed over Antarctic. If that had spread, 00:13:01.000 --> 00:13:12.000 to cut down the release of fluorocarbons seem to be helping 00:13:12.000 --> 00:13:23.000 with that. But, again, Penny will have more to say. 00:13:23.000 --> 00:13:34.000 Those of you who've lived around here for a little bit probably know 00:13:34.000 --> 00:13:45.000 that the fishing industry just locally has had a very hard time. 00:13:45.000 --> 00:13:56.000 There is a fishing boat just up in Gloucester, just up the coast less 00:13:56.000 --> 00:14:04.000 than an hour from here. And part of the problems, 00:14:04.000 --> 00:14:08.000 again, are caused by mismanagement of the resources where the fish have 00:14:08.000 --> 00:14:12.000 been, stocks have been over-fished so some of the fisheries have come 00:14:12.000 --> 00:14:17.000 to the point of collapse or near. Places such as the Grand Banks off 00:14:17.000 --> 00:14:21.000 of Newfoundland there has been a collapse, and it's not at all clear 00:14:21.000 --> 00:14:25.000 that it can be reversed and whether they'll be cod in large quantities 00:14:25.000 --> 00:14:31.000 every again there. OK. So there a variety of ways that we 00:14:31.000 --> 00:14:39.000 can study biology. And I think I'm going to begin by 00:14:39.000 --> 00:14:46.000 outlining how we do that. Biology is an experimental science 00:14:46.000 --> 00:14:54.000 and it's one of the really important themes that we'll run through 00:14:54.000 --> 00:15:00.000 in this course. You cannot study biology by just 00:15:00.000 --> 00:15:04.000 sitting down with a pen and paper in a room and thinking. 00:15:04.000 --> 00:15:08.000 You have to get out and find out what's there. You need to make 00:15:08.000 --> 00:15:12.000 observations. You need to try experiments. You need to formulate 00:15:12.000 --> 00:15:16.000 hypotheses and test them and either modify your hypothesis or reject it 00:15:16.000 --> 00:15:20.000 and so on. But it's a continual cycle of experimentation and making 00:15:20.000 --> 00:15:24.000 hypotheses and testing. It's the Scientific Method at work. 00:15:24.000 --> 00:15:29.000 But you can carry that out at different levels. 00:15:29.000 --> 00:15:39.000 The very highest level would be the biosphere. Here's one example. 00:15:39.000 --> 00:15:49.000 That's earth. It's here. There are many, many species of life that 00:15:49.000 --> 00:16:00.000 are on there. There are many more than a million. 00:16:00.000 --> 00:16:04.000 And the estimates of how many there are range from, 00:16:04.000 --> 00:16:09.000 in total, 10 to the 20 million estimated. And one of the big 00:16:09.000 --> 00:16:13.000 worries right at the moment is that as rain forests are being depleted, 00:16:13.000 --> 00:16:18.000 parts of the world that are a rich source of biological diversity, 00:16:18.000 --> 00:16:23.000 as those are disappearing we're losing diversity at quite a rate. 00:16:23.000 --> 00:16:27.000 Just a couple of years ago I had a chance to fly over 00:16:27.000 --> 00:16:32.000 a part of Brazil. And it was just scary to see from 00:16:32.000 --> 00:16:37.000 the plane how the rain forest was just being cut down. 00:16:37.000 --> 00:16:42.000 And you could just see how fast some of the rain forest was 00:16:42.000 --> 00:16:48.000 disappearing, and with it many different types of species that only 00:16:48.000 --> 00:16:53.000 can live there. One can look instead, 00:16:53.000 --> 00:16:58.000 going down a level, at an ecosystem which is a particular 00:16:58.000 --> 00:17:06.000 environment -- 00:17:06.000 --> 00:17:10.000 -- and the species of life found in it. And just to give you a couple 00:17:10.000 --> 00:17:14.000 of examples of that, it could be a salt marsh as shown 00:17:14.000 --> 00:17:18.000 here. Or here's an interesting environment that Penny Chisholm will 00:17:18.000 --> 00:17:22.000 tell you more about. This is a black smoker. 00:17:22.000 --> 00:17:26.000 There's a vent several miles deep in the Pacific Ocean. 00:17:26.000 --> 00:17:30.000 The water temperature that's gushing out of here is around 360 00:17:30.000 --> 00:17:35.000 degree centigrade. And there's a particular community 00:17:35.000 --> 00:17:40.000 of life that's able to grow around these deep vents. 00:17:40.000 --> 00:17:46.000 And Penny will tell you more about that. Then going down yet another 00:17:46.000 --> 00:17:56.000 level you can come to a population. 00:17:56.000 --> 00:18:07.000 And this is interacting -- 00:18:07.000 --> 00:18:11.000 -- or interbreeding organisms. An example might be the fiddler 00:18:11.000 --> 00:18:16.000 crabs in a salt marsh. Or here we see an interesting 00:18:16.000 --> 00:18:20.000 population. These are tube worms that are up to a meter or more in 00:18:20.000 --> 00:18:25.000 length that you find down at these black smokers. 00:18:25.000 --> 00:18:34.000 If we move down yet another level -- 00:18:34.000 --> 00:18:39.000 -- we come to organisms. Organisms have three important 00:18:39.000 --> 00:18:45.000 sorts of characteristics that we'll talk quite a bit about in this 00:18:45.000 --> 00:18:51.000 course. They carry out metabolism which is the sum of all the 00:18:51.000 --> 00:18:57.000 different chemical reactions necessary for life. 00:18:57.000 --> 00:19:07.000 They undergo regulated growth -- 00:19:07.000 --> 00:19:12.000 -- and they reproduce. And the sort of fundamental unit of 00:19:12.000 --> 00:19:17.000 life that we will talk about over and over again in this course is 00:19:17.000 --> 00:19:22.000 known as a cell. And life comes in two kinds of 00:19:22.000 --> 00:19:29.000 species. There is unicellular life where the 00:19:29.000 --> 00:19:37.000 organism is just a single cell and multicellular forms of life that are 00:19:37.000 --> 00:19:45.000 made of many different types of cells. What's a cell? 00:19:45.000 --> 00:19:53.000 One of the secrets to life. It's a little tiny bit of the 00:19:53.000 --> 00:20:02.000 universe that's surrounded by a boundary. 00:20:02.000 --> 00:20:07.000 And it's given the special name of a membrane. It's selective, 00:20:07.000 --> 00:20:12.000 not very permeable to most things. And cells are able to put little 00:20:12.000 --> 00:20:17.000 importers and exporters and things that control the passage of things 00:20:17.000 --> 00:20:22.000 across the membrane by isolating the inside of a cell from all the rest 00:20:22.000 --> 00:20:27.000 of the universe. That is one of the principles that 00:20:27.000 --> 00:20:32.000 makes life possible. We have a couple of examples of 00:20:32.000 --> 00:20:38.000 organisms here. Here are some clams that grow down 00:20:38.000 --> 00:20:43.000 at those black smokers, and they can get pretty large. 00:20:43.000 --> 00:20:49.000 And, as I say, Penny will talk a bit more about this. 00:20:49.000 --> 00:20:54.000 And we have this really amazing diversity of life forms that we find 00:20:54.000 --> 00:21:00.000 on this planet. However, if we think about this 00:21:00.000 --> 00:21:06.000 division into unicellular and multicellular organisms. 00:21:06.000 --> 00:21:10.000 Unicellular organisms include things that you're familiar with. 00:21:10.000 --> 00:21:15.000 They're bacteria. There is a picture of just E. 00:21:15.000 --> 00:21:20.000 coli cells. And we'll be talking about E. coli quite a bit as a model 00:21:20.000 --> 00:21:25.000 organism as we go through the course. By studying E. 00:21:25.000 --> 00:21:30.000 coli, scientists have learned many important things that apply 00:21:30.000 --> 00:21:35.000 to all of life. Another kind of important 00:21:35.000 --> 00:21:41.000 single-celled organism, unicellular organism is yeast. 00:21:41.000 --> 00:21:46.000 Those are pictures of yeast saccharomyces that are used in 00:21:46.000 --> 00:21:52.000 baking bread or in brewing beer or making wine. And another one you're 00:21:52.000 --> 00:21:58.000 all familiar with are algae which are single-celled organisms that are 00:21:58.000 --> 00:22:04.000 able to carry out photosynthesis. And we'll be talking about that. 00:22:04.000 --> 00:22:11.000 If we think of an example of a multicellular organism then we see 00:22:11.000 --> 00:22:18.000 there are different levels at which we can think about this. 00:22:18.000 --> 00:22:25.000 We could take, for example, a picture of me, just an 00:22:25.000 --> 00:22:32.000 anatomically correct diagram here, that I'm made up, as you are, of 00:22:32.000 --> 00:22:39.000 about ten to the fourteenth human cells. 00:22:39.000 --> 00:22:43.000 We all started out as a fertilized egg, which is a single cell. 00:22:43.000 --> 00:22:48.000 And by the time we're grown up, where we have about ten to the 00:22:48.000 --> 00:22:53.000 fourteenth human cells. Just a tremendous amount of cell 00:22:53.000 --> 00:22:58.000 growth that had to happen and specialization. 00:22:58.000 --> 00:23:02.000 The other thing you may not appreciate is that we have an 00:23:02.000 --> 00:23:07.000 ecosystem inside us in our gastrointestinal tract. 00:23:07.000 --> 00:23:11.000 This part, the intestine having the highest concentration of 00:23:11.000 --> 00:23:16.000 microorganisms. But there are about ten to the 00:23:16.000 --> 00:23:20.000 fourteenth bacteria also inside of our gut. So we're actually almost 00:23:20.000 --> 00:23:25.000 the same number of human cells and bacterial cells. 00:23:25.000 --> 00:23:29.000 And if we don't have those bacteria then our digestive systems 00:23:29.000 --> 00:23:35.000 don't work well. So if we go down from a whole 00:23:35.000 --> 00:23:41.000 organism, a whole multicellular organism, a level, 00:23:41.000 --> 00:23:47.000 then we come to an organ. An example of that might be an eye. 00:23:47.000 --> 00:23:53.000 And I think we have a diagram of an eye which is made up of different 00:23:53.000 --> 00:24:00.000 parts. If we go down another level we come to a tissue. 00:24:00.000 --> 00:24:07.000 Which is now you can begin to see that tissue are made up of groups of 00:24:07.000 --> 00:24:14.000 specialized cells. An example might be the retina of 00:24:14.000 --> 00:24:21.000 an eye. And if we continue to go downwards we'll get to single cells. 00:24:21.000 --> 00:24:28.000 And at this point we're at the same level of the tail as when we're 00:24:28.000 --> 00:24:35.000 talking about a unicellular organism. 00:24:35.000 --> 00:24:46.000 If we continue down then -- 00:24:46.000 --> 00:24:54.000 -- we can get to organelles. These are involved in energy 00:24:54.000 --> 00:25:04.000 production, energy management. 00:25:04.000 --> 00:25:10.000 And mitochondrion and chloroplasts are the two principle examples of 00:25:10.000 --> 00:25:16.000 organelles that we'll talk about. And if we go down yet another level 00:25:16.000 --> 00:25:22.000 of organization we get to molecules. And part of the reason that biology 00:25:22.000 --> 00:25:28.000 has flourished so well over the last few decades at MIT is there has been 00:25:28.000 --> 00:25:34.000 a real emphasis on looking at things at a cellular and molecular level. 00:25:34.000 --> 00:25:38.000 So you're going to be hearing a lot about cells and a lot about 00:25:38.000 --> 00:25:42.000 molecules as we go through this course. Here's an example of 00:25:42.000 --> 00:25:46.000 rhodopsin. That's a protein. We'll be talking about what 00:25:46.000 --> 00:25:50.000 proteins are, but it's a very important class of molecule in 00:25:50.000 --> 00:25:54.000 nature. In this case, proteins involved in sensing light 00:25:54.000 --> 00:25:59.000 and play an important part in your vision. 00:25:59.000 --> 00:26:02.000 Here is another protein. You cannot really tell what it's 00:26:02.000 --> 00:26:06.000 doing by just looking at it, but in this case this is one of the 00:26:06.000 --> 00:26:10.000 lethal factors that is made by anthrax. It's one of the proteins 00:26:10.000 --> 00:26:14.000 that anthrax makes that's capable of killing you if you get infected with 00:26:14.000 --> 00:26:18.000 it. Here's another molecule we'll talk about in great detail. 00:26:18.000 --> 00:26:22.000 This is DNA. You probably all know it's a double helix, 00:26:22.000 --> 00:26:26.000 two strands of DNA that are held together by forces we'll 00:26:26.000 --> 00:26:30.000 be discussing. It's an absolutely beautiful 00:26:30.000 --> 00:26:36.000 molecule. It's fascinated me through all of my life. 00:26:36.000 --> 00:26:41.000 And we'll be talking quite a bit about that as the course goes on. 00:26:41.000 --> 00:26:47.000 OK. So if we're thinking about cells there are two important kinds 00:26:47.000 --> 00:26:53.000 of cells that one finds on this planet. 00:26:53.000 --> 00:27:01.000 Prokaryotic cells. 00:27:01.000 --> 00:27:07.000 Prokaryotic organisms and eukaryotic organisms. 00:27:07.000 --> 00:27:14.000 They each are made of cells that are distinguishable from each other. 00:27:14.000 --> 00:27:20.000 I've indicated that a cell is a little bit of the universe that's 00:27:20.000 --> 00:27:27.000 surrounded by a boundary or a membrane. But inside there, 00:27:27.000 --> 00:27:34.000 inside of this is the DNA which functions as the genetic material. 00:27:34.000 --> 00:27:40.000 It's the blueprint for everything that that cell is going to make and 00:27:40.000 --> 00:27:47.000 be able to do. Ultimately everything is encoded 00:27:47.000 --> 00:27:53.000 there. And in a prokaryotic cell the DNA is free within this membrane. 00:27:53.000 --> 00:28:00.000 The eukaryotic cell also has a membrane. 00:28:00.000 --> 00:28:08.000 But the DNA inside is inside another membrane compartment known as the 00:28:08.000 --> 00:28:16.000 nucleus. And this is the DNA. These prokaryotic cells tend to be 00:28:16.000 --> 00:28:24.000 of the order of a kilometer in length. And eukaryotic cells are 00:28:24.000 --> 00:28:32.000 usually larger, can be ten to a hundred kilometers. 00:28:32.000 --> 00:28:36.000 There's quite a bit of variation, but that gives you at least some 00:28:36.000 --> 00:28:40.000 sense of the range. Now, I've for years, 00:28:40.000 --> 00:28:45.000 when I did a diagram like this, I wanted to somehow be able to show 00:28:45.000 --> 00:28:49.000 you that these cells were impressive than just what's on the board. 00:28:49.000 --> 00:28:54.000 So here are a couple of pictures to try and do that. 00:28:54.000 --> 00:28:58.000 This shows a picture of E. coli swimming along. And the way 00:28:58.000 --> 00:29:03.000 this image is being taken lets you see what are called flagella but 00:29:03.000 --> 00:29:07.000 which are basically the propellers that E. coli have that let it swim 00:29:07.000 --> 00:29:12.000 through the water. These are long structures made of 00:29:12.000 --> 00:29:17.000 proteins that are several times the body length of the bacterium. 00:29:17.000 --> 00:29:22.000 And there's a molecular motor imbedded in the bacterium that 00:29:22.000 --> 00:29:27.000 whirls it around at about somewhere between 10,000 and 100, 00:29:27.000 --> 00:29:32.000 00 RPM. And that's what drives the bacteria forward. 00:29:32.000 --> 00:29:36.000 So that was a prokaryotic cell. Here's a paramecium. This is a 00:29:36.000 --> 00:29:41.000 single-celled eukaryotic organism. And, as you can see here, it's 00:29:41.000 --> 00:29:46.000 capable of movement as well. In this case it has cilia along the 00:29:46.000 --> 00:29:51.000 outside that allow it to move. Here's an interesting one. I don't 00:29:51.000 --> 00:29:56.000 know if any of you can guess what these were. These were cells from 00:29:56.000 --> 00:30:01.000 the skin of a mouse. They're on an Auger surface. 00:30:01.000 --> 00:30:05.000 And, as you can see, they too can move. There are a 00:30:05.000 --> 00:30:10.000 couple of things that are important about this. I got this slide from 00:30:10.000 --> 00:30:14.000 Linda Griffith who is in the Biological Engineering Department. 00:30:14.000 --> 00:30:19.000 At the time I got it from her I think it was in Chemical Engineering 00:30:19.000 --> 00:30:23.000 several years ago. And what was important about this, 00:30:23.000 --> 00:30:28.000 apart from it being a very nice little movie showing you a mammalian 00:30:28.000 --> 00:30:32.000 cell moving around, was that I saw Linda show this 00:30:32.000 --> 00:30:37.000 during one of her research seminars. 00:30:37.000 --> 00:30:41.000 So here is an engineer at MIT who was showing this picture as part of 00:30:41.000 --> 00:30:45.000 her research talk. And I think those of you who are 00:30:45.000 --> 00:30:49.000 going onto engineering, you may be surprised at the extent 00:30:49.000 --> 00:30:53.000 to which you need to know about biology as you go through your 00:30:53.000 --> 00:31:01.000 professional careers. 00:31:01.000 --> 00:31:08.000 OK. So one of the great discoveries that has happened over the last few 00:31:08.000 --> 00:31:15.000 years that came out of our ability to look at DNA and RNA was the 00:31:15.000 --> 00:31:22.000 discovery that the forms of life that are prokaryotic actually split 00:31:22.000 --> 00:31:30.000 into two distinct Kingdoms that are very, very different. 00:31:30.000 --> 00:31:34.000 The archaea and the bacteria. And just to give you a sense of the 00:31:34.000 --> 00:31:39.000 diversity of life, I'll just mention a couple of these. 00:31:39.000 --> 00:31:44.000 These archaea look like bacteria but they are diverged from the 00:31:44.000 --> 00:31:49.000 bacteria as they are from the eukaryotes. So there were sort of 00:31:49.000 --> 00:31:54.000 three really major Kingdoms of Life. And the archaea, many of them can 00:31:54.000 --> 00:32:00.000 live in specialized environments. For example, sulfolobus can live at 00:32:00.000 --> 00:32:07.000 about 90 degrees centigrade and a pH of somewhere between 1 and 2. 00:32:07.000 --> 00:32:14.000 So if you see something like a hot springs, there are organisms such as 00:32:14.000 --> 00:32:21.000 this that are able to grow in that environment. Or there are halophyes, 00:32:21.000 --> 00:32:28.000 salt-loving archaea that can grow, for example, in formula sodium 00:32:28.000 --> 00:32:34.000 chloride. And if you've, 00:32:34.000 --> 00:32:38.000 for example, ever flown into San Francisco airport coming up from the 00:32:38.000 --> 00:32:42.000 south over San Jose, you've seen things that look sort of 00:32:42.000 --> 00:32:46.000 like these pictures where seawater is being evaporated down to collect 00:32:46.000 --> 00:32:51.000 the salt. And you'll see they're colored, and the reason they're 00:32:51.000 --> 00:32:55.000 colored is that these halobacteria are photobacteria that are able to 00:32:55.000 --> 00:32:59.000 use light as an energy source. And they make pigments that absorb 00:32:59.000 --> 00:33:04.000 the light, and that's why these salt areas get colored. 00:33:04.000 --> 00:33:11.000 A third example would be methanogens. These are organisms that produce 00:33:11.000 --> 00:33:18.000 methane. If you've walked into a lake and stepped on the bottom and 00:33:18.000 --> 00:33:25.000 seen little bubbles come up, those are little bubbles of methane. 00:33:25.000 --> 00:33:32.000 Or another place where you find methanogens are inside of cows. 00:33:32.000 --> 00:33:37.000 Now, some of you may not know that the cow is more or less a walking 00:33:37.000 --> 00:33:42.000 anaerobic fermentor here. If we have an anatomically correct 00:33:42.000 --> 00:33:47.000 picture of a cow. The inside of the cow, 00:33:47.000 --> 00:33:52.000 there's a large chamber known as the rumen where there's no oxygen, 00:33:52.000 --> 00:33:57.000 and there's a culture of microorganisms there that 00:33:57.000 --> 00:34:02.000 include methanogens. And it's this combination of 00:34:02.000 --> 00:34:07.000 microorganisms that enables cows to each grass that we cannot manage to 00:34:07.000 --> 00:34:12.000 get energy from. And as a byproduct of this 00:34:12.000 --> 00:34:17.000 specialized type of metabolism produces methane. 00:34:17.000 --> 00:34:23.000 And a cow burps something of the order of 400 liters a day of methane. 00:34:23.000 --> 00:34:28.000 OK. So one last thing then just to kind of pull this all together is 00:34:28.000 --> 00:34:33.000 that these organelles that I mentioned, which are also membrane 00:34:33.000 --> 00:34:38.000 compartments that are found in eukaryotic cells, are 00:34:38.000 --> 00:35:50.000 the mitochondria -- 00:35:50.000 --> 00:35:31.000 -- or chloroplast. There's pretty strong evidence at 00:35:31.000 --> 00:35:13.000 this point that these arose from bacteria that were things that 00:35:13.000 --> 00:35:07.000 you're more familiar with. Things like E. 00:35:07.000 --> 00:35:15.000 coli or streptococcus that causes strep throat or the lactic acid 00:35:15.000 --> 00:35:23.000 bacteria that causes the milk to turn into yogurt which some of you 00:35:23.000 --> 00:35:29.000 probably had for lunch today. That these organelles, 00:35:29.000 --> 00:35:33.000 the mitochondria and the chloroplast were derived from particular type of 00:35:33.000 --> 00:35:37.000 bacteria that probably first got transiently associated with 00:35:37.000 --> 00:35:41.000 developing eukaryotic cells sometime back in evolution, 00:35:41.000 --> 00:35:45.000 and eventually became captured and became a permanent part of the 00:35:45.000 --> 00:35:49.000 eukaryotic cell. The mitochondrion is thought to 00:35:49.000 --> 00:35:53.000 have derived from something that looks like today's present day 00:35:53.000 --> 00:35:57.000 rizobia, which we'll talk about, that form an intracellular infection 00:35:57.000 --> 00:36:02.000 of plants, or rickettsia which is chronic intracellular pathogen. 00:36:02.000 --> 00:36:05.000 The mitochondrion look as though they came from something related to 00:36:05.000 --> 00:36:09.000 that. The chloroplasts look as though they came from a bacterium 00:36:09.000 --> 00:36:13.000 that was able to carry on photosynthesis which we'll also be 00:36:13.000 --> 00:36:17.000 talking about. I want to close by giving you just 00:36:17.000 --> 00:36:21.000 a quick little snapshot of evolution because I'm hoping this will maybe 00:36:21.000 --> 00:36:25.000 make some of the things that we talk about in this course clearer. 00:36:25.000 --> 00:36:34.000 So what we're going to do is we're going to look back from 4. 00:36:34.000 --> 00:36:44.000 billion years ago when the earth was just forming -- 00:36:44.000 --> 00:36:57.000 -- to now. I'm just going to try 00:36:57.000 --> 00:37:03.000 and give you a few key sort of landmarks as we go along. 00:37:03.000 --> 00:37:09.000 So about 4.5 billion years ago there was methane, carbon dioxide, 00:37:09.000 --> 00:37:16.000 ammonium, hydrogen gas, nitrogen gas, water, but importantly no oxygen at 00:37:16.000 --> 00:37:22.000 that point. There was a lot of debate as to how life initially came. 00:37:22.000 --> 00:37:29.000 One of the prevalent theories at this point is there's something 00:37:29.000 --> 00:37:35.000 called an RNA world. This is just a hypothesis in which 00:37:35.000 --> 00:37:40.000 it's thought that perhaps the molecule RNA, which we'll talk about, 00:37:40.000 --> 00:37:45.000 played role as both something that was able to catalyze chemical 00:37:45.000 --> 00:37:51.000 reactions and therefore did things actively and also stored information. 00:37:51.000 --> 00:37:56.000 But, in any case, the best guess is that the first 00:37:56.000 --> 00:38:01.000 life that was about 3. billion years ago, somewhere in 00:38:01.000 --> 00:38:06.000 that vicinity. It was something that probably 00:38:06.000 --> 00:38:10.000 resembled most closely a present-day bacterium, a single-celled organism, 00:38:10.000 --> 00:38:14.000 something like that. Now, initially when life got started it's thought 00:38:14.000 --> 00:38:18.000 that there were a lot of organic chemicals that had been made as a 00:38:18.000 --> 00:38:22.000 consequence of lightening strikes and all sorts of chemistry that had 00:38:22.000 --> 00:38:26.000 happened so there was sort of a soup of some kind, some molecules 00:38:26.000 --> 00:38:31.000 that could be used. So probably these first organisms 00:38:31.000 --> 00:38:35.000 where able to basically use some preformed nutrients. 00:38:35.000 --> 00:38:40.000 And then as the soup began to get depleted by using it they had to 00:38:40.000 --> 00:38:44.000 learn to synthesize, at least develop systems that would 00:38:44.000 --> 00:38:49.000 synthesize these building blocks. And they also had to begin to worry 00:38:49.000 --> 00:38:54.000 about what to use as energy. And so somewhere in here, something 00:38:54.000 --> 00:38:58.000 that I'll call, in a silly way, photosynthesis 00:38:58.000 --> 00:39:03.000 released number one. But this was a system that enabled 00:39:03.000 --> 00:39:08.000 the organism to capture energy from sunlight so that it wasn't now 00:39:08.000 --> 00:39:14.000 dependent on getting energy by eating some preformed ingredient. 00:39:14.000 --> 00:39:19.000 It was then able to take carbon dioxide and make it into forms that 00:39:19.000 --> 00:39:24.000 were useful, of carbon that were useful for life, 00:39:24.000 --> 00:39:30.000 and it produced molecules such as sulfur as a waste product. 00:39:30.000 --> 00:39:36.000 There was a bit later in evolution, somewhere in here, something we 00:39:36.000 --> 00:39:43.000 might think of as photosynthesis release two. This was an improved 00:39:43.000 --> 00:39:49.000 version of photosynthesis. It captured more energy, worked 00:39:49.000 --> 00:39:56.000 better, but it developed, it had a waste product which was 00:39:56.000 --> 00:40:02.000 oxygen. Well, oxygen hadn't been in our 00:40:02.000 --> 00:40:06.000 atmosphere. And the first thing that sort of happened was that the 00:40:06.000 --> 00:40:10.000 world started to rust. All the iron, a lot of the iron 00:40:10.000 --> 00:40:14.000 started to interact with the oxygen. And Penny will tell you that at the 00:40:14.000 --> 00:40:19.000 base of the sea there are huge beds of iron oxide that came from this 00:40:19.000 --> 00:40:23.000 slow rusting of the earth. And so it took many, many years 00:40:23.000 --> 00:40:27.000 before oxygen levels started to rise. As you know it's about 20% of our 00:40:27.000 --> 00:40:32.000 atmosphere now. Even at this stage it was only a few 00:40:32.000 --> 00:40:37.000 percent of our, made up a few percent of our 00:40:37.000 --> 00:40:43.000 atmosphere, even by here in evolution. The first eukaryotic 00:40:43.000 --> 00:40:48.000 cell is thought to have appeared somewhere here. 00:40:48.000 --> 00:40:53.000 Again, it was likely a single-celled organism like some of 00:40:53.000 --> 00:40:59.000 those pictures I showed you. And evolution continued to go. 00:40:59.000 --> 00:41:04.000 Somewhere around a billion years ago sex was evolved which enabled 00:41:04.000 --> 00:41:09.000 eukaryotic organisms to exchange genetic material, 00:41:09.000 --> 00:41:15.000 and therefore evolve at a fast rate than they could previously. 00:41:15.000 --> 00:41:19.000 The Cambrian Period was about a 0. billion to 0.6 billion years ago. 00:41:19.000 --> 00:41:24.000 And there was a veritable explosion of life forms. 00:41:24.000 --> 00:41:28.000 And you can still see in the fossil records how much diversity was 00:41:28.000 --> 00:41:33.000 generated at that point, some of which went on to become life 00:41:33.000 --> 00:41:38.000 forms and other which probably were more evolutionary dead ends. 00:41:38.000 --> 00:41:46.000 Finally we get to the dinosaurs that were about 245 to 65 million years 00:41:46.000 --> 00:41:55.000 ago which would place them somewhere here on this timeline. 00:41:55.000 --> 00:42:04.000 So in honor of this course, I've commissioned a full scale model 00:42:04.000 --> 00:42:13.000 of anatomically correct [NOISE OBSCURES]. 00:42:13.000 --> 00:42:18.000 So we'll put our dinosaur here, if I can get him to stay put for a 00:42:18.000 --> 00:42:23.000 minute. All right. And at this point in evolution 00:42:23.000 --> 00:42:28.000 things started to get interesting. So somewhere about here, 4 million 00:42:28.000 --> 00:42:34.000 years ago we've got the first evidence of hominoids. 00:42:34.000 --> 00:42:39.000 Maybe 20,000 years ago we found the cave paintings in France. 00:42:39.000 --> 00:42:45.000 And then there was the Roman Empire and Columbus discovered America. 00:42:45.000 --> 00:42:51.000 And you were born and the Red Sox won the World Series and the 00:42:51.000 --> 00:42:57.000 Patriots have just won the Super Bowl. And we are now here at the 00:42:57.000 --> 00:43:03.000 peak of evolution which is, as you all know, the MIT student. 00:43:03.000 --> 00:43:06.000 So we'll put our MIT student here, who I can probably not get to stay 00:43:06.000 --> 00:43:10.000 put because you can never get MIT students to stay anywhere. 00:43:10.000 --> 00:43:14.000 But, in any case, this is sort of a silly demonstration. 00:43:14.000 --> 00:43:18.000 But there is a very profound reason why I'm doing it. 00:43:18.000 --> 00:43:22.000 And I must say I don't think I'd ever fully appreciated it until I 00:43:22.000 --> 00:43:26.000 actually thought of doing this demo for the class. 00:43:26.000 --> 00:43:30.000 But what I think you can see is that evolution, 00:43:30.000 --> 00:43:34.000 for the most part, happened at the single cell level. 00:43:34.000 --> 00:43:38.000 Many people tended to think evolution, that was about dinosaurs 00:43:38.000 --> 00:43:42.000 and all that stuff. We can say that dinosaurs are, 00:43:42.000 --> 00:43:47.000 practically now, most of evolution occurred at the level of single 00:43:47.000 --> 00:43:51.000 cells, and that all this amazing diversity we see around us was very 00:43:51.000 --> 00:43:56.000 recent embellishments in evolution. So that means when you study 00:43:56.000 --> 00:44:00.000 biology at the cellular and molecular level you find tremendous 00:44:00.000 --> 00:44:04.000 commonalities. If you look inside a sulfolobus 00:44:04.000 --> 00:44:08.000 growing in hot spring, if you look inside an E. 00:44:08.000 --> 00:44:12.000 coli, if you look inside a yeast and you look inside one of our cells you 00:44:12.000 --> 00:44:16.000 find that, to a huge extent, many, many of the cellular 00:44:16.000 --> 00:44:20.000 components are common. They arose similarly in evolution 00:44:20.000 --> 00:44:24.000 that they're shared by all forms of life. Of course, 00:44:24.000 --> 00:44:28.000 there are some things that developed later and are different. 00:44:28.000 --> 00:44:32.000 But that's one of the reasons that you can learn so much by studying 00:44:32.000 --> 00:44:36.000 biology at the cellular molecular level and why we'll emphasize it a 00:44:36.000 --> 00:44:41.000 fair bit in this course. The other thing that I'd like to 00:44:41.000 --> 00:44:45.000 make out of this, a theme that you'll hear along is 00:44:45.000 --> 00:44:50.000 that organisms modify their environment. You can see that in 00:44:50.000 --> 00:44:54.000 the case of oxygen back when the earth formed. There was no oxygen 00:44:54.000 --> 00:44:59.000 in our atmosphere. Now we have a lot of it. 00:44:59.000 --> 00:45:03.000 The reason it's there is because it was generated by organisms carrying 00:45:03.000 --> 00:45:08.000 out photosynthesis and generating oxygen as a waste product. 00:45:08.000 --> 00:45:13.000 And that was an absolutely critical thing to enable creatures such as 00:45:13.000 --> 00:45:18.000 ourselves, which are dependent on oxygen for us just to be alive, 00:45:18.000 --> 00:45:23.000 if we hadn't had this change in environment things like us could 00:45:23.000 --> 00:45:28.000 have, organisms like us couldn't have evolved. 00:45:28.000 --> 00:45:32.000 So, anyway, I hope that will give you a little sort of snapshot of 00:45:32.000 --> 00:45:37.000 evolution and will help guide your understanding of this course. 00:45:37.000 --> 00:45:40.000 We'll see you at the next lecture.