WEBVTT 00:00:00.000 --> 00:00:04.000 Let's get started. So I'm going to finish up energy 00:00:04.000 --> 00:00:09.000 today. And then we're going to begin sort of section more or less 00:00:09.000 --> 00:00:14.000 we'll call it molecular biology but it's sort of dealing with the issues 00:00:14.000 --> 00:00:19.000 that revolve around the discovery that DNA was the genetic material 00:00:19.000 --> 00:00:24.000 and then working through how people understood how information got from 00:00:24.000 --> 00:00:29.000 the DNA into everything else, how things were regulated. 00:00:29.000 --> 00:00:32.000 There are an incredibly large number of important discoveries that form 00:00:32.000 --> 00:00:36.000 the foundation of how we think about biology that are going to come out 00:00:36.000 --> 00:00:40.000 in this next section, but before I do that I just want to 00:00:40.000 --> 00:00:44.000 finish up this section that I talked to you about, about energy. 00:00:44.000 --> 00:00:48.000 And I hope as we go along here you're going to see how some of 00:00:48.000 --> 00:00:52.000 these sort of disparate parts of the course begin to come together. 00:00:52.000 --> 00:00:56.000 Almost everything we're going to be talking about now is going to be 00:00:56.000 --> 00:01:00.000 needing energy such as replicating DNA or making proteins and 00:01:00.000 --> 00:01:04.000 all sorts of things. And those are driven ultimately by 00:01:04.000 --> 00:01:09.000 ATP. And what I've been trying to talk to about for the last lecture 00:01:09.000 --> 00:01:14.000 or two is how the cell gets the ATP, the energy money that it needs to 00:01:14.000 --> 00:01:19.000 make things. We talked through glycolysis, this ancient, 00:01:19.000 --> 00:01:24.000 ancient way of getting a couple of ATPs out of a molecule of sugar so 00:01:24.000 --> 00:01:29.000 well-imbedded in our genetic makeup it's in almost all organisms. 00:01:29.000 --> 00:01:33.000 And then I talked last lecture about this other principle which must have 00:01:33.000 --> 00:01:37.000 come up very, very early in evolution. Again, 00:01:37.000 --> 00:01:42.000 it's used by all organisms. And that's the principle of 00:01:42.000 --> 00:01:46.000 capturing the energy that's inherent in a proton gradient across a 00:01:46.000 --> 00:01:51.000 membrane. And I talked to you then about the idea then the way it 00:01:51.000 --> 00:01:55.000 worked was that the cell would have something in its membrane that would 00:01:55.000 --> 00:01:59.000 be a proton pump and it would pump the proton from one side of the 00:01:59.000 --> 00:02:04.000 membrane to the other. So it's working against the gradient. 00:02:04.000 --> 00:02:09.000 So it's doing energy. So there are a couple of different 00:02:09.000 --> 00:02:14.000 ways energy needs to be provided. It could be provided by some kind 00:02:14.000 --> 00:02:19.000 of light energy, and that's what drives 00:02:19.000 --> 00:02:24.000 photosynthesis. I'll say a few words about that. 00:02:24.000 --> 00:02:29.000 Or in the case of respiration with the oxidative phosphorylation, 00:02:29.000 --> 00:02:34.000 I showed you how it was the electrons sort of descend in 00:02:34.000 --> 00:02:39.000 stepwise fashion down from one state to another. 00:02:39.000 --> 00:02:44.000 There's energy given off, free energy is available, and that 00:02:44.000 --> 00:02:50.000 can be used to power the pump. And once the proton gradient is 00:02:50.000 --> 00:02:56.000 made then the cells can turn it around and use the energy that's in 00:02:56.000 --> 00:03:01.000 that proton gradient to make ATP. So in respiration remember the trick 00:03:01.000 --> 00:03:05.000 was then to take those two pyruvates, burn them all the way down to carbon 00:03:05.000 --> 00:03:10.000 dioxide and water, make as many ATPs and NADHs as you 00:03:10.000 --> 00:03:14.000 could, then take the NADHs, use them to make a proton gradient 00:03:14.000 --> 00:03:19.000 and eventually, if you will, convert everything into 00:03:19.000 --> 00:03:23.000 ATP so you've got it as energy. Our cells do it. That part, 00:03:23.000 --> 00:03:28.000 respiration and the oxidative phosphorylation is done in 00:03:28.000 --> 00:03:32.000 mitochondria, which I said sort of came from bacteria that were 00:03:32.000 --> 00:03:37.000 captured at some point. Here's a picture of a mitochondrion. 00:03:37.000 --> 00:03:41.000 It still looks more or less like a bacterium. And I showed you the 00:03:41.000 --> 00:03:46.000 little parts that are in there. It was funny. Right after lecture 00:03:46.000 --> 00:03:50.000 I went back to my lab. I picked up a recent issue of 00:03:50.000 --> 00:03:55.000 Science. And I opened up to a page that said something about rats that 00:03:55.000 --> 00:04:00.000 had been bred to be very poor at aerobic exercise. 00:04:00.000 --> 00:04:03.000 And it went on to talk about the health problems they had. 00:04:03.000 --> 00:04:07.000 And there was a sentence in there that they think the underlying cause 00:04:07.000 --> 00:04:10.000 is by breeding these rats and selection four rats that are poor at 00:04:10.000 --> 00:04:14.000 doing aerobic exercise. What they think it all stems from 00:04:14.000 --> 00:04:17.000 is having very inefficient mitochondria that don't work nearly 00:04:17.000 --> 00:04:21.000 as well. And that would make a lot of sense. I was going to scan that 00:04:21.000 --> 00:04:24.000 article but we had some technical issues this morning. 00:04:24.000 --> 00:04:28.000 Maybe I can show it to you next lecture. OK. 00:04:28.000 --> 00:04:32.000 So the one last thing then that I want to do is I want to say a few 00:04:32.000 --> 00:04:37.000 words about photosynthesis because that actually preceded respiration. 00:04:37.000 --> 00:04:41.000 Respiration couldn't evolve until there was oxygen in the atmosphere. 00:04:41.000 --> 00:04:46.000 So probably the first use or certainly one of the first uses of 00:04:46.000 --> 00:04:51.000 the proton gradient happened in this scale of evolution and put here 00:04:51.000 --> 00:04:55.000 somewhere maybe 3. billion years ago or so when what I 00:04:55.000 --> 00:05:04.000 had called photosynthesis -- 00:05:04.000 --> 00:05:09.000 -- release I on day one in the sort of trivial fashion. This 00:05:09.000 --> 00:05:16.000 is known as cyclic -- 00:05:16.000 --> 00:05:22.000 -- photo phosphorylation. And the principle is relatively 00:05:22.000 --> 00:05:29.000 simple. It's to capture the energy in sunlight -- 00:05:29.000 --> 00:05:37.000 -- to make a proton gradient. 00:05:37.000 --> 00:05:43.000 And that then can be used, as you now know, to make ATP. 00:05:43.000 --> 00:05:50.000 So in order to capture energy from sunlight nature had to evolve 00:05:50.000 --> 00:05:56.000 molecules that are able to observe in the appropriate wavelength 00:05:56.000 --> 00:06:01.000 range. You know the names of those 00:06:01.000 --> 00:06:05.000 molecules. Chlorophyll, the come in two principle species. 00:06:05.000 --> 00:06:08.000 You don't have to remember the structure. What you can see is a 00:06:08.000 --> 00:06:12.000 lot of conjugated double-bonds. That's how you sort of tune the 00:06:12.000 --> 00:06:15.000 absorption of a molecule. If you want to make it absorb a 00:06:15.000 --> 00:06:19.000 longer and longer wavelength you start hooking together double bonds. 00:06:19.000 --> 00:06:22.000 And you can set it up sort of you can get a molecule to absorb at just 00:06:22.000 --> 00:06:26.000 about any maximum absorption, any wavelength you want. So 00:06:26.000 --> 00:06:30.000 chlorophyll is able to absorb this energy. 00:06:30.000 --> 00:06:34.000 And the principle of this is what happens. You have this chlorophyll 00:06:34.000 --> 00:06:39.000 and it absorbs a photon. And an electron gets excited so it 00:06:39.000 --> 00:06:44.000 basically moves to another orbital. It's farther away from the nucleus. 00:06:44.000 --> 00:06:49.000 It's easier now for that electron to get lost than it was before. 00:06:49.000 --> 00:06:54.000 Now, if nothing was happening that electron would eventually just fall 00:06:54.000 --> 00:06:59.000 down to its ground state and you'd lose all the energy as heat. 00:06:59.000 --> 00:07:05.000 So what happens in photosynthesis, though, is that the electron falls 00:07:05.000 --> 00:07:11.000 back down to the ground state again in a series of steps. 00:07:11.000 --> 00:07:17.000 And how this happens, electrons are basically getting 00:07:17.000 --> 00:07:23.000 passed from one carrier to another. And the same principle as we saw in 00:07:23.000 --> 00:07:29.000 respiration applies in that at each phase in here a proton is pumped. 00:07:29.000 --> 00:07:35.000 Now, the out and the in are reversed from what it says in respiration. 00:07:35.000 --> 00:07:41.000 You have notes on respiration, or should anyway. 00:07:41.000 --> 00:07:48.000 But the in and the out, as you'll see, it's sort of an 00:07:48.000 --> 00:07:54.000 arbitrary. You sort of take a frame of reference and then something's in 00:07:54.000 --> 00:07:59.000 and something's out. The point is that in both of them 00:07:59.000 --> 00:08:03.000 protons go from one side of the membrane to the other and you get 00:08:03.000 --> 00:08:07.000 more on one side, you pump them in one direction and 00:08:07.000 --> 00:08:11.000 they flow back in the other. And the in and the out is sort of 00:08:11.000 --> 00:08:15.000 an arbitrary way of describing what's happening, 00:08:15.000 --> 00:08:19.000 but in both cases the key thing is that you're pumping electrons out. 00:08:19.000 --> 00:08:23.000 And then these can be used to make ATP, as we talked about with ATP 00:08:23.000 --> 00:08:27.000 synthesis. In this case the electrons eventually end up back on 00:08:27.000 --> 00:08:30.000 the chlorophyll. And so that's why it's called cyclic 00:08:30.000 --> 00:08:34.000 phosphorylation. What you get out of this, 00:08:34.000 --> 00:08:37.000 as you can see, is ATP. So this was probably a really big deal in 00:08:37.000 --> 00:08:41.000 evolution because the current thinking is perhaps there was an RNA 00:08:41.000 --> 00:08:44.000 world that's still sort of being debated. At some point it's clear 00:08:44.000 --> 00:08:48.000 that somewhere around 3. billion years or so something that 00:08:48.000 --> 00:08:51.000 looks sort of like a present-day bacterium arose, 00:08:51.000 --> 00:08:55.000 probably eight molecules that had already been made in the sort of 00:08:55.000 --> 00:08:58.000 primordial soup, but when those started to run out 00:08:58.000 --> 00:09:02.000 then it needed other ways of making energy. 00:09:02.000 --> 00:09:07.000 It needed other ways of making carbon. Here's a way of getting 00:09:07.000 --> 00:09:12.000 energy, but what's available to make more organic molecules is only 00:09:12.000 --> 00:09:17.000 carbon dioxide. And if you remember that little 00:09:17.000 --> 00:09:22.000 thing I showed you of if we're going from a methyl to a hydroxyl to an 00:09:22.000 --> 00:09:29.000 aldehyde to an acid -- 00:09:29.000 --> 00:09:33.000 -- to CO2, that direction is oxidation and that direction is 00:09:33.000 --> 00:09:38.000 reduction. So if we go in that direction and we end up generating 00:09:38.000 --> 00:09:42.000 NADH because we're taking electrons and giving them to something else, 00:09:42.000 --> 00:09:47.000 if we want to go the other way if we're starting with C02 what we need 00:09:47.000 --> 00:09:52.000 to do is we need to have a supply of reducing power so we can take the 00:09:52.000 --> 00:09:56.000 C02 and get it down to all the less-oxidized states that are 00:09:56.000 --> 00:10:01.000 necessary for building all the molecules that we've 00:10:01.000 --> 00:10:06.000 been talking about. So making ATP was a great idea, 00:10:06.000 --> 00:10:10.000 but the cell still needed to have some form of reducing agent. 00:10:10.000 --> 00:10:15.000 And what they used was they used hydrogen sulfide. 00:10:15.000 --> 00:10:19.000 This is at least one of the major ways that it was done. 00:10:19.000 --> 00:10:24.000 And so there is a very slight twist here. This is NADP. 00:10:24.000 --> 00:10:28.000 It's the same molecule as NAD except there's an extra 00:10:28.000 --> 00:10:33.000 phosphorylation. And the one with the phosphate on it 00:10:33.000 --> 00:10:37.000 tends to be used in biosynthetic reactions, but otherwise it's 00:10:37.000 --> 00:10:41.000 exactly the same thing. It's an electron banking thing. 00:10:41.000 --> 00:10:45.000 And what this gave was NADPH plus sulfur plus a hydrogen. 00:10:45.000 --> 00:10:50.000 So sulfur is a waste product. Here's the reducing power. Here's 00:10:50.000 --> 00:10:54.000 the ATP. That's what those organisms need to be able to 00:10:54.000 --> 00:10:58.000 synthesize new organic material without having to have 00:10:58.000 --> 00:11:03.000 pre-made molecules. A really big deal in evolution. 00:11:03.000 --> 00:11:07.000 And the idea for making ATP is based on this use of establishing a 00:11:07.000 --> 00:11:12.000 proton gradient, the same principle we've seen again. 00:11:12.000 --> 00:11:17.000 Now, there's another possible source of reducing power, 00:11:17.000 --> 00:11:21.000 and that would be to use water as the source of the reducing power. 00:11:21.000 --> 00:11:26.000 But in order to do that you've got to put more energy into it. 00:11:26.000 --> 00:11:31.000 And this system wasn't able to handle it. 00:11:31.000 --> 00:11:43.000 But that happened soon enough with the development of what I called on 00:11:43.000 --> 00:11:55.000 the first day photosynthesis release II, which is technically known as 00:11:55.000 --> 00:12:04.000 noncyclic photophosphorylation. Again, it uses the energy of 00:12:04.000 --> 00:12:08.000 sunlight. But the twist this time, it not only makes ATP, it also makes 00:12:08.000 --> 00:12:13.000 NADPH, it makes reducing power at the same time. 00:12:13.000 --> 00:12:17.000 So you can see that is a really major advance. 00:12:17.000 --> 00:12:22.000 If you can use sunlight to make both of them now you're really 00:12:22.000 --> 00:12:26.000 efficient. So this is how this one works. It's related 00:12:26.000 --> 00:12:31.000 to the other one. And the first part is more or less 00:12:31.000 --> 00:12:36.000 the same idea. A photon is absorbed by a molecule 00:12:36.000 --> 00:12:42.000 of chlorophyll. It kicks the chlorophyll up to an 00:12:42.000 --> 00:12:47.000 activated state where the electrons are at a higher orbital far away. 00:12:47.000 --> 00:12:52.000 It wants to come back down. Energy is going to be released. 00:12:52.000 --> 00:12:58.000 So electrons gets passed, protons get pumped from one side of 00:12:58.000 --> 00:13:04.000 a membrane to another. Except this time, 00:13:04.000 --> 00:13:10.000 instead of coming back this lands in a different chlorophyll that has 00:13:10.000 --> 00:13:16.000 just recently lost a pair of electrons. But there's a new energy 00:13:16.000 --> 00:13:22.000 input here that kicks this chlorophyll up to an even higher 00:13:22.000 --> 00:13:28.000 energy state than this one. And as these electrons start to 00:13:28.000 --> 00:13:34.000 come down the energy hill there's enough energy here to take a 00:13:34.000 --> 00:13:40.000 molecule of NADP+ plus a hydrogen ion and give NADPH. 00:13:40.000 --> 00:13:46.000 There's one thing that this isn't going to work like a cycle or a 00:13:46.000 --> 00:13:53.000 machine yet. Anybody see what hasn't been taken care of yet? 00:13:53.000 --> 00:14:00.000 Say again. Send the electrons back to this chlorophyll, exactly. 00:14:00.000 --> 00:14:05.000 However, the way the energetics are structured now the cells were able 00:14:05.000 --> 00:14:10.000 to take reducing power from here and generate 2H+ plus a half of an 00:14:10.000 --> 00:14:16.000 oxygen molecule. And this would really be two waters 00:14:16.000 --> 00:14:21.000 giving four hydrogens and one oxygen molecule. So what you can see here 00:14:21.000 --> 00:14:27.000 now, there are a couple of really important things about this. 00:14:27.000 --> 00:14:33.000 It needs more energy. It makes ATP and NADPH which leaves 00:14:33.000 --> 00:14:41.000 the cell able to carry out biosynthesis. And the third thing, 00:14:41.000 --> 00:14:48.000 which is an incredible influence on our planet, it started to generate 00:14:48.000 --> 00:14:56.000 oxygen as a waste product. And it's really a mixed blessing. 00:14:56.000 --> 00:15:01.000 I mean oxygen is very reactive. It damages our DNA. 00:15:01.000 --> 00:15:05.000 It damages our proteins. We have an amazing number of 00:15:05.000 --> 00:15:08.000 defenses against oxygen. But, on the other hand, as it 00:15:08.000 --> 00:15:11.000 accumulated in the atmosphere and organisms slowly over evolutionary 00:15:11.000 --> 00:15:15.000 time learned to deal with it, it then set us up for the 00:15:15.000 --> 00:15:18.000 possibility of respiration which, as you can see, is 18 times more 00:15:18.000 --> 00:15:21.000 efficient than in that ancient way of using glycolysis to make energy 00:15:21.000 --> 00:15:25.000 out of sugars. So that's more or less the story. 00:15:25.000 --> 00:15:29.000 This part is called photosystem II. 00:15:29.000 --> 00:15:34.000 This assembly of stuff is photosystem I. 00:15:34.000 --> 00:15:39.000 And I just wanted to show you this next slide because chlorophyll isn't 00:15:39.000 --> 00:15:44.000 just floating around like this. As you might guess, it's bound into 00:15:44.000 --> 00:15:49.000 proteins and things. And someone has figured out the 00:15:49.000 --> 00:15:54.000 structure of photosystem I. It consists of 12 proteins, 00:15:54.000 --> 00:16:00.000 96 chlorophylls and about 30 other molecules. 00:16:00.000 --> 00:16:04.000 And what it really does is it functions as an antenna. 00:16:04.000 --> 00:16:08.000 Some of the other molecules can absorb it at wavelengths that are 00:16:08.000 --> 00:16:12.000 different from chlorophyll. And all the energy gets funneled 00:16:12.000 --> 00:16:16.000 into the chlorophyll and into this process. And you'll probably 00:16:16.000 --> 00:16:20.000 recognize by now that proteins here we're seeing alpha helices and beta 00:16:20.000 --> 00:16:24.000 sheets in here as part of this structure. So the first organisms 00:16:24.000 --> 00:16:28.000 that learned how to do this were organisms we now know 00:16:28.000 --> 00:16:32.000 as cyanobacteria. They're a kind of bacteria that has 00:16:32.000 --> 00:16:36.000 two membranes like E. coli and like the other ones that 00:16:36.000 --> 00:16:41.000 we've talked about. You're familiar with these. 00:16:41.000 --> 00:16:45.000 There's the green scum you see on ponds. Here's a close-up. 00:16:45.000 --> 00:16:50.000 Sometimes they grow as filaments, the cells in a chain. You notice 00:16:50.000 --> 00:16:54.000 they're green. They're making chlorophyll. 00:16:54.000 --> 00:16:59.000 And what happened in plants was that apparently something probably 00:16:59.000 --> 00:17:03.000 related to the present-day cyanobacteria got trapped inside 00:17:03.000 --> 00:17:08.000 some early progenitor of what we now know as plants and green algae. 00:17:08.000 --> 00:17:15.000 And this trapped bacterium became a chloroplast. And it had all the 00:17:15.000 --> 00:17:23.000 machinery necessary to carry out this noncyclic photophosphorylation. 00:17:23.000 --> 00:17:31.000 The structure of these things, there's an outer membrane. 00:17:31.000 --> 00:17:35.000 Just similar to what I told you for the mitochondria. 00:17:35.000 --> 00:17:40.000 There's an inner membrane. And what's special about the 00:17:40.000 --> 00:17:45.000 mitochondrion then, there's another membrane inside 00:17:45.000 --> 00:17:54.000 that's known as the thylocoid. 00:17:54.000 --> 00:18:00.000 And that's where all the chlorophyll is. And the reason the out and the 00:18:00.000 --> 00:18:07.000 in is a little bit confusing in here is this part, which is probably the 00:18:07.000 --> 00:18:14.000 cytoplasm of the old bacterium, is pumped from what's known as the 00:18:14.000 --> 00:18:21.000 stroma of a chloroplast which is equivalent to the cytoplasm of the 00:18:21.000 --> 00:18:27.000 original bacteria into the lumen. So the chlorophyll that's in this 00:18:27.000 --> 00:18:32.000 membrane absorbs the light, pumps protons into the lumen 00:18:32.000 --> 00:18:37.000 building up a proton gradient, and then they flow back out in the 00:18:37.000 --> 00:18:42.000 other direction and make ATP. Here's a picture of a chloroplast 00:18:42.000 --> 00:18:47.000 once again. It looks an awful lot like the bacterium still that got 00:18:47.000 --> 00:18:52.000 captured. All this stuff on the inside, those are the thylocoid 00:18:52.000 --> 00:18:57.000 membranes that carry out this specialized stuff. So 00:18:57.000 --> 00:19:01.000 there you have it. That's how cells, 00:19:01.000 --> 00:19:05.000 the major ways that life has figured out how to make energy. 00:19:05.000 --> 00:19:08.000 When Penny Chisholm starts to talk to you she'll talk to you about how 00:19:08.000 --> 00:19:12.000 organisms adapt to various niches, things that live in the bottom of 00:19:12.000 --> 00:19:15.000 the ocean, things that live in various places. 00:19:15.000 --> 00:19:19.000 They all have to make energy. Well, they all use some variation 00:19:19.000 --> 00:19:22.000 on these principles I've talked to you about. And she'll then show you 00:19:22.000 --> 00:19:26.000 how they're very cleaver at extracting energy out of all sorts 00:19:26.000 --> 00:19:30.000 of things by applying these principles in different ways. 00:19:30.000 --> 00:19:34.000 OK. So what we're going to start doing now is we're going to start 00:19:34.000 --> 00:19:39.000 talking about DNA. This is certainly a molecule that's 00:19:39.000 --> 00:19:43.000 fascinated me all my life. You should know from the first part 00:19:43.000 --> 00:19:48.000 that it's built up of units known as nucleotides that have a sugar. 00:19:48.000 --> 00:19:53.000 It's a ribose sugar that's missing one hydroxyl so it's a deoxyribose. 00:19:53.000 --> 00:19:57.000 The sugars are numbered 1, 2, 3, 4, 5. I showed you that. They'll be a 00:19:57.000 --> 00:20:02.000 phosphate. And then one of these nucleic acid 00:20:02.000 --> 00:20:06.000 bases, either a pyrimidine or a purine. And in DNA you find the 00:20:06.000 --> 00:20:11.000 pyrimidine bases are cytosine and thiamine. And in DNA the purine 00:20:11.000 --> 00:20:15.000 bases are adenine and guanine. And then these subunits are 00:20:15.000 --> 00:20:20.000 polymerized together. In essence, splitting out water to 00:20:20.000 --> 00:20:24.000 give you a polymer. And I didn't emphasize this too 00:20:24.000 --> 00:20:29.000 strong the first time I showed it to you. 00:20:29.000 --> 00:20:33.000 It's going to become a very big deal over the next few lectures as we 00:20:33.000 --> 00:20:37.000 begin to consider how nature had to figure out how to replicate DNA and 00:20:37.000 --> 00:20:42.000 all sorts of implications to go along with this, 00:20:42.000 --> 00:20:46.000 but there's a polarity to a strand of DNA. This is what's called the 5 00:20:46.000 --> 00:20:51.000 prime sugar. The primes indicate the numbers referring to the sugar, 00:20:51.000 --> 00:20:55.000 and the ones without primes are referring to numbers of atoms that 00:20:55.000 --> 00:21:00.000 make up part of the nucleic acid base. 00:21:00.000 --> 00:21:04.000 So if we're looking at a chain, this is a 5 prime carbon of the 00:21:04.000 --> 00:21:09.000 sugar, that's the 3 prime. And so what you can see, this bond 00:21:09.000 --> 00:21:14.000 which is really a phosphodiester bond, the phosphate group has formed 00:21:14.000 --> 00:21:19.000 an ester with this hydroxyl and with the hydroxyl that used to be here. 00:21:19.000 --> 00:21:24.000 So it's a phosphodiester bond and it's a 5 prime, 00:21:24.000 --> 00:21:29.000 3 prime bond. It joins the 5 prime carbon to the 3 prime 00:21:29.000 --> 00:21:33.000 carbon up here. So that means if you're looking at a 00:21:33.000 --> 00:21:37.000 chain of DNA, if you come down this way you're coming in the 5 to 3 00:21:37.000 --> 00:21:41.000 prime direction. If we come up the other way we're 00:21:41.000 --> 00:21:45.000 coming from the 3 prime end heading towards the 5 prime end. 00:21:45.000 --> 00:21:48.000 So you'll see me saying 5 prime, 3 prime. Now, as I told you, the 00:21:48.000 --> 00:21:52.000 principle force that holds the strands of the DNA together are 00:21:52.000 --> 00:21:56.000 hydrogen bonds, three of them between a G and a C 00:21:56.000 --> 00:22:00.000 and two of them between an A and a T. 00:22:00.000 --> 00:22:04.000 And then they are a pair of strands. And they're actually running in 00:22:04.000 --> 00:22:08.000 opposite polarities. This is something to contend with 00:22:08.000 --> 00:22:12.000 when we think about replication. 5 prime to 3 prime in one direction 00:22:12.000 --> 00:22:16.000 and 5 prime to 3 prime going in the opposite way here. 00:22:16.000 --> 00:22:21.000 And then, as you all know, it's called the double helix. 00:22:21.000 --> 00:22:25.000 So it's actually not flat like this in space. It's in a 3-dimensional 00:22:25.000 --> 00:22:29.000 twisted into a double helix and the base pairs are held together by 00:22:29.000 --> 00:22:33.000 hydrogen bonds between the bases on the opposite strands down the middle 00:22:33.000 --> 00:22:37.000 of the molecule. And I like this little movie I 00:22:37.000 --> 00:22:41.000 showed you because you can see it pretty well. The nitrogens are blue. 00:22:41.000 --> 00:22:44.000 It's easy to see the bases. And the hydrogen bonds are right in 00:22:44.000 --> 00:22:48.000 the middle. There's another force I didn't mention and it doesn't matter 00:22:48.000 --> 00:22:51.000 for this course, but when the bases sort of stack on 00:22:51.000 --> 00:22:55.000 top of each other there's actually a kind of extra stabilization that 00:22:55.000 --> 00:22:58.000 comes from that. It's a gorgeous molecule. 00:22:58.000 --> 00:23:02.000 You all know it encodes the genetic information. 00:23:02.000 --> 00:23:05.000 We're going to be talking about it a lot, but first thing, 00:23:05.000 --> 00:23:09.000 you know, I could just tell you it's the genetic information. 00:23:09.000 --> 00:23:13.000 But one of the really big discoveries in biology was that DNA 00:23:13.000 --> 00:23:16.000 is the genetic information. And a point I'm trying to help you 00:23:16.000 --> 00:23:20.000 learn here, you know, I'm trying to teach you more than 00:23:20.000 --> 00:23:24.000 just facts. And I hope some of you at least will catch that. 00:23:24.000 --> 00:23:28.000 I'm trying to show you how biology is done. 00:23:28.000 --> 00:23:31.000 As an experimental scientist you don't sit down usually and figure it 00:23:31.000 --> 00:23:34.000 out. Instead you start doing experiments and you get all kinds of 00:23:34.000 --> 00:23:38.000 unexpected discoveries. And, in general, as people work in 00:23:38.000 --> 00:23:41.000 these unexpected discoveries ultimately they come to these grand 00:23:41.000 --> 00:23:45.000 new insights that, you know, sometimes would have been 00:23:45.000 --> 00:23:48.000 very hard to forget. So the real question that people 00:23:48.000 --> 00:23:52.000 wondered for a long time, and we'll talk more about the 00:23:52.000 --> 00:23:55.000 history of genetics, but people knew we clearly had 00:23:55.000 --> 00:23:59.000 inheritable traits. You could see it in your kids. 00:23:59.000 --> 00:24:03.000 People had been breeding plants and all sorts of things. 00:24:03.000 --> 00:24:07.000 Breeding domestic animals. They sort of understood the 00:24:07.000 --> 00:24:11.000 principle of inheritance. When I tell you about Mendel we'll 00:24:11.000 --> 00:24:15.000 begin to see how his thinking led to the idea that the inheritance wasn't 00:24:15.000 --> 00:24:19.000 just sort of like a liquid where everything mixed together. 00:24:19.000 --> 00:24:23.000 It came in units or particles which we know of as genes. 00:24:23.000 --> 00:24:27.000 And so the idea that genes had been accepted certainly by the beginning 00:24:27.000 --> 00:24:31.000 of this century anyway, but nobody knew what they were made 00:24:31.000 --> 00:24:37.000 of. They were made of -- The major properties that they had 00:24:37.000 --> 00:24:44.000 was they clearly encoded information in some way. 00:24:44.000 --> 00:24:50.000 They must replicate because one cell 00:24:50.000 --> 00:24:54.000 could give two and on and on and on. So if you were going to pass it 00:24:54.000 --> 00:24:58.000 down in an inherited way they have to be replicated. 00:24:58.000 --> 00:25:01.000 And the third thing was that people knew somehow they could mutate or 00:25:01.000 --> 00:25:05.000 the information content that they encoded could be changed. 00:25:05.000 --> 00:25:09.000 Again, you could see that, that you'd get something, an altered 00:25:09.000 --> 00:25:13.000 characteristic, and then it would be propagated down 00:25:13.000 --> 00:25:16.000 through that line. That was the principle of breeding 00:25:16.000 --> 00:25:20.000 that people had done for ages. And so they understood that. There 00:25:20.000 --> 00:25:24.000 was one other key thing they knew. They knew that these genes were in 00:25:24.000 --> 00:25:28.000 the nucleus. And I'll tell you the full story of how even that insight 00:25:28.000 --> 00:25:32.000 was arrived at. But I'll just show you for the 00:25:32.000 --> 00:25:36.000 moment this little movie. This shows some chromosomes that 00:25:36.000 --> 00:25:40.000 are all bunched up and are just pulled apart at the time of the cell 00:25:40.000 --> 00:25:44.000 division. Those chromosomes, as we now know, are made of DNA. 00:25:44.000 --> 00:25:48.000 But in essence what people had seen through the microscope was these 00:25:48.000 --> 00:25:52.000 chromosomes or colored things that they could stain. 00:25:52.000 --> 00:25:56.000 They could sort of see something had doubled. And just before the 00:25:56.000 --> 00:26:01.000 cell divided the two sets separated and each cell got a new set. 00:26:01.000 --> 00:26:05.000 So that's about what people knew. They had those properties. They're 00:26:05.000 --> 00:26:10.000 in the nucleus. They knew about as much as you do. 00:26:10.000 --> 00:26:15.000 They knew the major classes of biomolecules in a cell. 00:26:15.000 --> 00:26:20.000 So what do you think you would need to do to show that DNA is the 00:26:20.000 --> 00:26:25.000 genetic material, encodes the genes? 00:26:25.000 --> 00:26:30.000 Find somebody near you. I'll give you a minute or so. 00:26:30.000 --> 00:26:32.000 I'd like to hear what kind of ideas you come up with. 00:26:32.000 --> 00:26:35.000 Then I'll tell you how it happened. But I want to hear. Why don't you 00:26:35.000 --> 00:26:37.000 think about it and just see if you can come up with a couple ideas for 00:26:37.000 --> 00:27:13.000 me, what you'd need to figure out. 00:27:13.000 --> 00:27:17.000 Well, let's just see what kind of ideas anybody got. 00:27:17.000 --> 00:27:21.000 If you wanted to make me believe that DNA is doing that, 00:27:21.000 --> 00:27:25.000 or I think it's a protein for the moment, that's what I think is most 00:27:25.000 --> 00:27:30.000 likely, but what you do think? Anybody got an idea? 00:27:30.000 --> 00:27:36.000 Mess up the DNA and see if we can mess up the cell. 00:27:36.000 --> 00:27:42.000 How are we going to do that? I can break a cell open and I guess 00:27:42.000 --> 00:27:48.000 I can purify DNA and I can analyze it. And it's got four bases in it 00:27:48.000 --> 00:27:54.000 and it's got sugars and phosphates. At that point nobody could sequence 00:27:54.000 --> 00:28:00.000 DNA. We didn't even know the structure. 00:28:00.000 --> 00:28:04.000 Yeah? Take it out of one cell and put it into another. 00:28:04.000 --> 00:28:08.000 And what would you expect to happen then? 00:28:08.000 --> 00:28:17.000 OK. That's a really nice idea. 00:28:17.000 --> 00:28:21.000 Somehow if you took the DNA and moved it from one cell to another 00:28:21.000 --> 00:28:26.000 that the characteristic of this cell would be somehow carried 00:28:26.000 --> 00:28:31.000 over. OK. That's in fact the way it happened 00:28:31.000 --> 00:28:35.000 but not as simply as that, as I'll tell you, but that's exactly 00:28:35.000 --> 00:28:39.000 the essence of it. One little problem. 00:28:39.000 --> 00:28:43.000 Maybe we'll see if anybody has a thought on this. 00:28:43.000 --> 00:28:47.000 If I purify DNA, I mean nothing's ever really pure, 00:28:47.000 --> 00:28:51.000 right? You get it out and there's always little bits of stuff. 00:28:51.000 --> 00:28:55.000 And someone can always argue, well, yeah, it's 99% DNA, but it's 00:28:55.000 --> 00:29:00.000 the other bits you cannot get rid of. Yeah? 00:29:00.000 --> 00:29:03.000 If you used radioactive material, how is that going to help us? 00:29:03.000 --> 00:29:13.000 It does contain nitrogen. 00:29:13.000 --> 00:29:25.000 Well, it gets a little complicated. 00:29:25.000 --> 00:29:31.000 Certainly nucleic acids have like phosphate in them, but so does RNA. 00:29:31.000 --> 00:29:36.000 That's going to be hard. Maybe if I had a mixture of things 00:29:36.000 --> 00:29:41.000 and I wanted to prove whether something was let's say DNA, 00:29:41.000 --> 00:29:46.000 a protein or something, you need some really specific way of saying I 00:29:46.000 --> 00:29:51.000 did something to the DNA and not to the protein or something like that. 00:29:51.000 --> 00:29:56.000 Have you heard anything in this course that is really specific? 00:29:56.000 --> 00:30:02.000 Enzymes. Do you think that'd give you an idea of how you might do it? 00:30:02.000 --> 00:30:06.000 If I've got a tube and it's mostly DNA and maybe a bit of protein and 00:30:06.000 --> 00:30:10.000 something, and let's say his idea is working, that we can take the DNA 00:30:10.000 --> 00:30:14.000 from this cell and put it over into the second cell and see the 00:30:14.000 --> 00:30:19.000 characteristic change, if I wanted to do something to show 00:30:19.000 --> 00:30:23.000 that it was the DNA in the tube that was responsible, 00:30:23.000 --> 00:30:27.000 could you use an enzyme? And what kind of enzyme would you 00:30:27.000 --> 00:30:32.000 want? Well, what characteristics would you like it to have? 00:30:32.000 --> 00:30:38.000 Nature's probably made it for you already. Something that synthesizes 00:30:38.000 --> 00:30:44.000 DNA? Something that breaks down DNA? Say I treated this tube with some 00:30:44.000 --> 00:30:50.000 kind of enzyme and then I wanted to see the outcome, 00:30:50.000 --> 00:30:56.000 what would we want, an enzyme that did what? 00:30:56.000 --> 00:31:00.000 Anybody else got an idea? You're asserting that it's the DNA 00:31:00.000 --> 00:31:04.000 in my prep, I like your idea, but I need to prove it so I need to 00:31:04.000 --> 00:31:07.000 do something to show that it's actually the DNA and not the other 00:31:07.000 --> 00:31:11.000 stuff. So if I had an enzyme that did what to DNA? 00:31:11.000 --> 00:31:14.000 If I broke it down, yeah. We could treat it. 00:31:14.000 --> 00:31:18.000 And if your idea is right, we treat the stuff with something 00:31:18.000 --> 00:31:21.000 that specifically breaks down DNA it won't get transferred. 00:31:21.000 --> 00:31:25.000 Does that make sense? OK. I mean that's a way you could go at 00:31:25.000 --> 00:31:28.000 a proof of this. And, in fact, that's what happened. 00:31:28.000 --> 00:31:32.000 But I'm going to quickly tell you how it actually happened. 00:31:32.000 --> 00:31:36.000 And again, you know, as I say, I'm trying to tell you a 00:31:36.000 --> 00:31:40.000 few things that are besides here are the facts that you need to know on 00:31:40.000 --> 00:31:44.000 exam. There's a bigger picture here and this is how research goes, 00:31:44.000 --> 00:31:48.000 and particularly in an experimental science such as biology. 00:31:48.000 --> 00:31:52.000 The important early work on this came from a guy who was known as 00:31:52.000 --> 00:31:56.000 Frederick Griffith. He was in London. He was a 00:31:56.000 --> 00:32:00.000 physician. He was working in the 1920s. 00:32:00.000 --> 00:32:11.000 And he was studying pneumonia. That's an infection of the lungs -- 00:32:11.000 --> 00:32:20.000 -- by bacteria. 00:32:20.000 --> 00:32:25.000 There's more than one kind of bacterium that will cause pneumonia, 00:32:25.000 --> 00:32:30.000 but one of the really important ones clinically was streptococcus -- 00:32:30.000 --> 00:32:38.000 -- pneumonia. So it was a bacterium. 00:32:38.000 --> 00:32:43.000 It was given that name. We all have bacterium on us. 00:32:43.000 --> 00:32:49.000 I think I told you we have about ten to the twelfth on our skin, 00:32:49.000 --> 00:32:54.000 for example. And if streptococcus is on your skin it's not a problem, 00:32:54.000 --> 00:32:59.000 but if it gets into your lungs it's a problem. And so to live with all 00:32:59.000 --> 00:33:05.000 these bacteria with us our bodies have defenses. 00:33:05.000 --> 00:33:08.000 So we have this immune system, we'll talk about more, and a bunch 00:33:08.000 --> 00:33:11.000 of defender cells. Things that you know as white blood 00:33:11.000 --> 00:33:14.000 cells are defenders. Let's just see here. 00:33:14.000 --> 00:33:18.000 I'm going to show you this little movie. This is one of your white 00:33:18.000 --> 00:33:21.000 blood cells, a special kind of white blood cell. That little thing it's 00:33:21.000 --> 00:33:24.000 chasing is a bacterium. These round things are red blood 00:33:24.000 --> 00:33:28.000 cells. I mean doesn't it look like a dog going after a mouse, 00:33:28.000 --> 00:33:32.000 or a cat going after something? It's chasing it. 00:33:32.000 --> 00:33:36.000 It can tell it's there. This is remarkable. And it's a 00:33:36.000 --> 00:33:41.000 little pixilated, but this is real. It's going to 00:33:41.000 --> 00:33:45.000 catch it right about there. And it eats it. I mean we have 00:33:45.000 --> 00:33:49.000 these cells inside us. That's why you don't die even 00:33:49.000 --> 00:33:54.000 though we live in a world that's surrounded by bacteria. 00:33:54.000 --> 00:33:58.000 OK, so we'll go on. So getting pneumonia in those days was 00:33:58.000 --> 00:34:03.000 a really bad thing. You get infected, 00:34:03.000 --> 00:34:07.000 you get this in your lungs, and then you have four to six days this. So that's the bacterium. 00:34:07.000 --> 00:34:12.000 of high fever, and then the patient would reach Well, it turns out that streptococcus is a bacteria like 00:34:12.000 --> 00:34:17.000 what's termed as a ìcrisisî. And one of two things would happen. 00:34:17.000 --> 00:34:21.000 They'd either live or they'd die. And that was it. 00:34:21.000 --> 00:34:26.000 I mean this was no fun if somebody you knew had it because you didn't 00:34:26.000 --> 00:34:27.000 know the outcome. And the outcome wasn't necessarily 00:34:27.000 --> 00:34:23.000 very good. Now you call up the doctor and they pump you full of 00:34:23.000 --> 00:34:19.000 antibiotics, but antibiotics hadn't been discovered yet. 00:34:19.000 --> 00:34:15.000 So this was pretty serious business, and people were trying to understand 00:34:15.000 --> 00:34:11.000 what was happening. But what was going on during these 00:34:11.000 --> 00:34:07.000 four to six days that then led to one of these two outcomes? 00:35:07.000 --> 00:35:11.000 And it has around it something known as a capsule. And what that capsule 00:35:11.000 --> 00:35:15.000 is polysaccharide. Remember back to the second lecture 00:35:15.000 --> 00:35:19.000 when I was confusing you all by showing you how sugars could hook 00:35:19.000 --> 00:35:23.000 together in all a manner of different ways? 00:35:23.000 --> 00:35:27.000 Well, that's what polysaccharides are. You just hook a bunch 00:35:27.000 --> 00:35:31.000 of sugars together. And for this course you don't have 00:35:31.000 --> 00:35:34.000 to remember the linkages in particular. You just have to 00:35:34.000 --> 00:35:37.000 understand that there are different kinds of linkages, 00:35:37.000 --> 00:35:40.000 and every time you hook at it in a different way you get a different 00:35:40.000 --> 00:35:43.000 kind of polysaccharide out of it. But anyway, the bacterium make this 00:35:43.000 --> 00:35:46.000 capsule of polysaccharide. And it's full of hydroxyl groups 00:35:46.000 --> 00:35:49.000 from all those sugars so it attracts a lot of water around it. 00:35:49.000 --> 00:35:52.000 And what it does is it causes a problem for those defender cells 00:35:52.000 --> 00:35:55.000 that we just saw. Those would be, for example, 00:35:55.000 --> 00:35:59.000 a macrophagic kind of white blood cell. 00:35:59.000 --> 00:36:02.000 And it cannot eat something that's got the capsule. 00:36:02.000 --> 00:36:06.000 Now, here's a picture of one of these capsules on one of these kinds 00:36:06.000 --> 00:36:10.000 of bacteria. You can sort of see it out here. It's polysaccharide. 00:36:10.000 --> 00:36:14.000 That's the main part of the bacterium. And here's another 00:36:14.000 --> 00:36:18.000 pixilated thing of one of these white blood cells eating a bacterium 00:36:18.000 --> 00:36:22.000 that doesn't have a capsule. But watch what happens if the 00:36:22.000 --> 00:36:26.000 bacterium has a capsule. It cannot get a hold of it. 00:36:26.000 --> 00:36:30.000 It just cannot quite grab hold of it. So what happened during those 00:36:30.000 --> 00:36:34.000 days, though, was this capsule which is a foreign entity to your body 00:36:34.000 --> 00:36:38.000 gets recognized in your immune system. 00:36:38.000 --> 00:36:42.000 And your immune system made antibodies that could recognize that. 00:36:42.000 --> 00:36:47.000 We'll talk about what these are, but all you need to know for the 00:36:47.000 --> 00:36:52.000 moment is that they're proteins and they can be tuned to recognize some 00:36:52.000 --> 00:36:57.000 chemical entity with a very, very high degree of specificity. 00:36:57.000 --> 00:37:02.000 So what the body was doing during this thing was trying to make 00:37:02.000 --> 00:37:07.000 antibodies that would help it recognize this capsule. 00:37:07.000 --> 00:37:10.000 And then it decorates the capsule with these things. 00:37:10.000 --> 00:37:14.000 And once it puts antibodies stuck all over the surface now it can get 00:37:14.000 --> 00:37:18.000 a hold of it. And, again, a fact you don't have to know. 00:37:18.000 --> 00:37:22.000 This whole process is called opsonization. The reason they use 00:37:22.000 --> 00:37:26.000 the word opsin because opsin is the Greek word for seasoning. 00:37:26.000 --> 00:37:30.000 And it was as if these white blood cells liked to have their bacteria 00:37:30.000 --> 00:37:34.000 seasoned correctly before they can eat them. 00:37:34.000 --> 00:37:37.000 And what's really going on is that they're decorating them with 00:37:37.000 --> 00:37:40.000 antibodies. So what was going on after a person got sick, 00:37:40.000 --> 00:37:43.000 it was a race between their immune system trying to make antibodies 00:37:43.000 --> 00:37:47.000 which would let their immune system suppress the infection and the 00:37:47.000 --> 00:37:50.000 bacterium which is replicating unchecked for the first few days. 00:37:50.000 --> 00:37:53.000 And that's why it was such a scary business, because you didn't know 00:37:53.000 --> 00:37:57.000 what the outcome was and things could tip it one way 00:37:57.000 --> 00:38:03.000 or the other. Well, this did suggest a kind of 00:38:03.000 --> 00:38:13.000 therapy. The kind of therapy would be to isolate a capsule 00:38:13.000 --> 00:38:25.000 to inject a horse. 00:38:25.000 --> 00:38:28.000 Get the antibodies from the horse. Why a horse? A horse is huge, 00:38:28.000 --> 00:38:32.000 right? It makes a lot of antibodies. 00:38:32.000 --> 00:38:39.000 A lot better than injecting a mouse if you want to get antibodies. 00:38:39.000 --> 00:38:46.000 So get antibodies and then inject the patient. It's a good idea in 00:38:46.000 --> 00:38:53.000 principle. So you're sort of short-circuiting this whole process. 00:38:53.000 --> 00:39:00.000 The problem was there were more than 20 kinds of capsules. 00:39:00.000 --> 00:39:07.000 And so what people had to do was they had to isolate 00:39:07.000 --> 00:39:17.000 the bacterium -- 00:39:17.000 --> 00:39:30.000 -- from the patient, determine the type of capsule. 00:39:30.000 --> 00:39:35.000 Let's say it's sort of from capsule 1 up to capsule type 20, 00:39:35.000 --> 00:39:40.000 which one it was, and then inject the correct antibody. 00:39:40.000 --> 00:39:46.000 So this was nerve-racking because it took a while for the bacteria to 00:39:46.000 --> 00:39:51.000 grow so it was a pretty tight time window. And if you saw the patient 00:39:51.000 --> 00:39:57.000 right away that's good, but if they were partway down the 00:39:57.000 --> 00:40:02.000 infection not so good. So the one other thing to do this, 00:40:02.000 --> 00:40:06.000 they didn't bother all the way to isolate the capsule. 00:40:06.000 --> 00:40:10.000 What they would usually do is use heat-killed bacteria and then you'd 00:40:10.000 --> 00:40:14.000 have the capsule and everything. The bacterium is dead, it cannot do 00:40:14.000 --> 00:40:19.000 anything, and they'd inject the horse with that. 00:40:19.000 --> 00:40:23.000 And that would get you the antibodies with the capsule. 00:40:23.000 --> 00:40:27.000 So what Griffith was doing was he was fiddling around 00:40:27.000 --> 00:40:32.000 with this system. And there was one other discovery 00:40:32.000 --> 00:40:36.000 that he made. Perhaps it wouldn't surprise you that since the bacteria 00:40:36.000 --> 00:40:40.000 surrounded by a molecule absorbs water that the capsules would look 00:40:40.000 --> 00:40:45.000 sort of glistening. They absorbed a lot of water. 00:40:45.000 --> 00:40:49.000 You can see how they look here. So what they discovered was if they 00:40:49.000 --> 00:40:54.000 have a capsule you get what are called smooth colonies. 00:40:54.000 --> 00:40:58.000 And the word colony in this thing just refers to it started out as one 00:40:58.000 --> 00:41:03.000 bacterium and it kept dividing and dividing and dividing. 00:41:03.000 --> 00:41:07.000 And maybe there are ten to the eighth or ten to the ninth bacteria 00:41:07.000 --> 00:41:11.000 in that little colony. But you can see it. They've all 00:41:11.000 --> 00:41:15.000 got capsules on the outside so it attracts a lot of water and it looks 00:41:15.000 --> 00:41:19.000 wet. And those are what you saw. But what they found is if you 00:41:19.000 --> 00:41:23.000 waited or grew the cultures up that you would see some things that 00:41:23.000 --> 00:41:27.000 looked dry or they called them rough. And these turned out to be bacteria 00:41:27.000 --> 00:41:33.000 that lacked a capsule. And so if you might start with a 00:41:33.000 --> 00:41:40.000 smooth strain S here and then isolate from it a rough strain it 00:41:40.000 --> 00:41:48.000 might designate it in that kind of way. So this is the sort of thing 00:41:48.000 --> 00:41:55.000 that Griffith was fooling around with. So he started with doing this 00:41:55.000 --> 00:42:02.000 kind of experiment. He took a smooth strain making a 00:42:02.000 --> 00:42:08.000 capsule type two, OK? So he was injecting a mouse 00:42:08.000 --> 00:42:14.000 with this. And what happened was the mouse was dead. 00:42:14.000 --> 00:42:20.000 This was a virulent form of the bacterium. So if he took the rough 00:42:20.000 --> 00:42:26.000 mutant, injected the mouse, the mouse is alive and you saw why. 00:42:26.000 --> 00:42:32.000 If it doesn't have a capsule, 00:42:32.000 --> 00:42:36.000 the mouse has defender cells and white blood cells could eat it. 00:42:36.000 --> 00:42:41.000 Then he had heat-killed S3. So this was a strain of streptococcus 00:42:41.000 --> 00:42:46.000 that had a different capsule, a type 3 capsule, but it was 00:42:46.000 --> 00:42:50.000 heat-killed. Why was he working with heat-killed stuff? 00:42:50.000 --> 00:42:55.000 Because that's what you injected the horses with to get it. 00:42:55.000 --> 00:43:00.000 So what do you think would happen here? 00:43:00.000 --> 00:43:06.000 Since the bacteria are dead, probably not a big surprise the 00:43:06.000 --> 00:43:13.000 mouse is alive. Now, I don't know whether he did 00:43:13.000 --> 00:43:19.000 this on purpose or he did it as a control, but what he did was he 00:43:19.000 --> 00:43:26.000 injected at the same time then R2 plus heat-killed S3. 00:43:26.000 --> 00:43:32.000 So he's got two things that don't do anything, he injects a mouse, 00:43:32.000 --> 00:43:38.000 and uh-oh, the mouse dies. That is a weird result. 00:43:38.000 --> 00:43:42.000 That is actually also, though, the first really key step to 00:43:42.000 --> 00:43:47.000 understanding that DNA is a genetic material. It doesn't look like it 00:43:47.000 --> 00:43:52.000 at this point probably, but it was. This is how we learned 00:43:52.000 --> 00:43:56.000 this really enormous fact from these experiments. He wasn't trying 00:43:56.000 --> 00:44:00.000 to figure it out. He was trying to work out something 00:44:00.000 --> 00:44:04.000 else, as you can see, but it was a bizarre finding. 00:44:04.000 --> 00:44:08.000 So what would you think? I've put in something that used to have a R2 00:44:08.000 --> 00:44:12.000 capsule. So did it get rejuvenated somehow by this heat-killed thing or, 00:44:12.000 --> 00:44:16.000 as you'd suggested, did some characteristic get 00:44:16.000 --> 00:44:20.000 transferred from here or whatever? So he isolated the bacteria out of 00:44:20.000 --> 00:44:24.000 this, and what he found now was he had a live bacterium 00:44:24.000 --> 00:44:29.000 that was making S3. So something had been transferred 00:44:29.000 --> 00:44:35.000 from this set of dead bacteria into bacteria that were alive, 00:44:35.000 --> 00:44:41.000 and the characteristic had been passed from the dead bacterium to 00:44:41.000 --> 00:44:47.000 the new bacterium, the other bacterium. 00:44:47.000 --> 00:44:53.000 So this is about what Griffith did, but this problem was picked up by a 00:44:53.000 --> 00:44:59.000 scientist at Rockefeller, Oswald Avery who worked as part of a 00:44:59.000 --> 00:45:04.000 team. And he took this finding and started 00:45:04.000 --> 00:45:10.000 to work on it and tried to figure out, because he saw in this result a 00:45:10.000 --> 00:45:16.000 way of finding out what was the genetic material because somehow 00:45:16.000 --> 00:45:21.000 what was in that heat-killed S3 was the stuff that would transfer 00:45:21.000 --> 00:45:27.000 genetic information into another bacterium. So he made one 00:45:27.000 --> 00:45:31.000 really big discovery. And that was you didn't need the 00:45:31.000 --> 00:45:35.000 mouse at all. All that was happening was the mouse, 00:45:35.000 --> 00:45:38.000 by dying, was in essence selecting for smooth bacteria. 00:45:38.000 --> 00:45:42.000 So he could simplify things by just taking a rough bacteria, 00:45:42.000 --> 00:45:45.000 taking the heat-killed extract, putting it in, and now he'd just 00:45:45.000 --> 00:45:49.000 look for smooth colonies. Didn't need any mice at all. 00:45:49.000 --> 00:45:52.000 So he was able to see the characteristic of the capsule being 00:45:52.000 --> 00:45:56.000 transferred from some kind of heat-killed mess of things into a 00:45:56.000 --> 00:46:00.000 rough bacterium and changing it into a live bacterium. 00:46:00.000 --> 00:46:04.000 So he started fractionating, and he did exactly the kind of this was called transformation. 00:46:04.000 --> 00:46:08.000 approach that you suggested. And he purified and he purified and matters in the thing was taking DNA and putting it in. 00:46:08.000 --> 00:46:12.000 he purified using as his assay this ability to pass on this smooth 00:46:12.000 --> 00:46:16.000 characteristic. And what he ended up with was 00:46:16.000 --> 00:46:20.000 virtually pure DNA but, as I said, you know, always never 00:46:20.000 --> 00:46:24.000 quite pure. And somebody can always argue, well, you've got a little bit 00:46:24.000 --> 00:46:28.000 of something else in there. So he did a really key experiment 00:46:28.000 --> 00:46:33.000 and he treated with DNAs, your experiment. 00:46:33.000 --> 00:46:00.000 And it lost the transforming activity. So this process of doing plasma and you stick it into E. coli so you can grow it up, that 00:45:50.000 --> 00:46:04.000 Initially it described that phenomenon. Now that we know what 00:46:18.000 --> 00:46:33.000 So if you do a UROP somewhere here, you clone a piece of DNA into a 00:46:47.000 --> 00:47:01.000 process of taking the naked DNA and putting it inside the bacteria, 00:47:01.000 --> 00:47:11.000 you'll call it transformation. Now, in fact, this result wasn't 00:47:11.000 --> 00:47:16.000 accepted right away. This was published in 1944. 00:47:16.000 --> 00:47:20.000 And the general realization that DNA was the genetic material really 00:47:20.000 --> 00:47:25.000 didn't come until the ë50s. Yet this result proved it, if you 00:47:25.000 --> 00:47:30.000 will, but part of the problem was the world wasn't yet ready to accept 00:47:30.000 --> 00:47:34.000 that DNA was a genetic material. And maybe you can see the problem. 00:47:34.000 --> 00:47:37.000 It looked like a monotonous molecule. It only had four things 00:47:37.000 --> 00:47:40.000 that were different in it. And if you isolated they were all 00:47:40.000 --> 00:47:43.000 often kind of there and about the same amount. People thought it was 00:47:43.000 --> 00:47:46.000 just an analyst GATC. It didn't sound like anything had 00:47:46.000 --> 00:47:49.000 encoded information. Proteins looked really attractive. 00:47:49.000 --> 00:47:52.000 Twenty different amino acids that all had different characteristics, 00:47:52.000 --> 00:47:55.000 so that was a great place for storing information. 00:47:55.000 --> 00:47:58.000 So the world wasn't quite ready to accept it, even though the 00:47:58.000 --> 00:48:02.000 experimental evidence was there. And so the result came later. 00:48:02.000 --> 00:48:07.000 Now, the last thing I just want to show you, because there's a kind of 00:48:07.000 --> 00:48:12.000 direct link from that Avery experiment to you guys because a 00:48:12.000 --> 00:48:17.000 year or two ago it was the 50th anniversary of the discovery of DNA. 00:48:17.000 --> 00:48:22.000 And Avery worked with a team of two other people called MacLeod and 00:48:22.000 --> 00:48:27.000 McCarty. This was at the 50th anniversary, the meeting down at 00:48:27.000 --> 00:48:32.000 Cold Spring Harbor celebrating it. McCarty was the only member of the 00:48:32.000 --> 00:48:36.000 team alive. There he was. I asked him to autograph my program. 00:48:36.000 --> 00:48:41.000 There was his signature. He just died a little while ago, 00:48:41.000 --> 00:48:45.000 and so there's no living connection to that anymore, 00:48:45.000 --> 00:48:50.000 but I have a picture to show you guys that takes you back from that 00:48:50.000 --> 00:48:54.000 experiment to his signature right there. OK? So I'll tell you some 00:48:54.000 --> 00:48:57.000 more stuff next lecture. Have a good weekend.