WEBVTT 00:00:00.470 --> 00:00:03.210 Considering that I have a cold right now, I can't imagine a 00:00:03.210 --> 00:00:08.109 more appropriate topic to make a video on than a virus. 00:00:08.109 --> 00:00:09.930 And I didn't want to make it that thick. 00:00:09.930 --> 00:00:11.380 A virus, or viruses. 00:00:14.760 --> 00:00:19.080 And in my opinion, viruses are, on some level, the most 00:00:19.080 --> 00:00:21.450 fascinating thing in all of biology. 00:00:21.450 --> 00:00:25.560 Because they really blur the boundary between what is an 00:00:25.560 --> 00:00:27.440 inanimate object and what is life? 00:00:30.080 --> 00:00:33.410 I mean if we look at ourselves, or life as one of 00:00:33.410 --> 00:00:35.210 those things that you know it when you see it. 00:00:35.210 --> 00:00:39.300 If you see something that, it's born, it grows, it's 00:00:39.300 --> 00:00:40.460 constantly changing. 00:00:40.460 --> 00:00:41.510 Maybe it moves around. 00:00:41.510 --> 00:00:42.260 Maybe it doesn't. 00:00:42.260 --> 00:00:44.400 But it's metabolizing things around itself. 00:00:44.400 --> 00:00:46.310 It reproduces and then it dies. 00:00:46.310 --> 00:00:48.300 You say, hey, that's probably life. 00:00:48.300 --> 00:00:50.960 And in this, we throw most things that we see-- or we 00:00:50.960 --> 00:00:52.815 throw in, us. 00:00:52.815 --> 00:00:55.360 We throw in bacteria. 00:00:55.360 --> 00:00:57.120 We throw in plants. 00:00:57.120 --> 00:01:00.830 I mean, I could-- I'm kind of butchering the taxonomy system 00:01:00.830 --> 00:01:03.275 here, but we tend to know life when we see it. 00:01:03.275 --> 00:01:07.480 But all viruses are, they're just a bunch of genetic 00:01:07.480 --> 00:01:09.740 information inside of a protein. 00:01:09.740 --> 00:01:11.230 Inside of a protein capsule. 00:01:11.230 --> 00:01:13.490 So let me draw. 00:01:13.490 --> 00:01:16.340 And the genetic information can come in any form. 00:01:16.340 --> 00:01:22.240 So it can be an RNA, it could be DNA, it could be 00:01:22.240 --> 00:01:24.670 single-stranded RNA, double-stranded RNA. 00:01:24.670 --> 00:01:27.260 Sometimes for single stranded they'll write these two little 00:01:27.260 --> 00:01:29.250 S's in front of it. 00:01:29.250 --> 00:01:30.950 Let's say they are talking about double stranded DNA, 00:01:30.950 --> 00:01:32.910 they'll put a ds in front of it. 00:01:32.910 --> 00:01:35.330 But the general idea-- and viruses can come in all of 00:01:35.330 --> 00:01:38.110 these forms-- is that they have some genetic information, 00:01:38.110 --> 00:01:40.530 some chain of nucleic acids. 00:01:40.530 --> 00:01:43.730 Either as single or double stranded RNA or single or 00:01:43.730 --> 00:01:44.560 double stranded DNA. 00:01:44.560 --> 00:01:47.970 And it's just contained inside some type of protein 00:01:47.970 --> 00:01:49.880 structure, which is called the capsid. 00:01:49.880 --> 00:01:53.240 And kind of the classic drawing is kind of an 00:01:53.240 --> 00:01:56.650 icosahedron type looking thing. 00:01:56.650 --> 00:01:58.200 Let me see if I can do justice to it. 00:01:58.200 --> 00:02:00.610 It looks something like this. 00:02:00.610 --> 00:02:02.800 And not all viruses have to look exactly like this. 00:02:02.800 --> 00:02:05.160 There's thousands of types of viruses. 00:02:05.160 --> 00:02:06.850 And we're really just scratching the surface and 00:02:06.850 --> 00:02:09.630 understanding even what viruses are out there and all 00:02:09.630 --> 00:02:14.800 of the different ways that they can essentially replicate 00:02:14.800 --> 00:02:15.220 themselves. 00:02:15.220 --> 00:02:16.620 We'll talk more about that in the future. 00:02:16.620 --> 00:02:19.110 And I would suspect that pretty much any possible way 00:02:19.110 --> 00:02:21.530 of replication probably does somehow exist 00:02:21.530 --> 00:02:22.750 in the virus world. 00:02:22.750 --> 00:02:25.260 But they really are just these proteins, these protein 00:02:25.260 --> 00:02:27.450 capsids, are just made up of a bunch of little 00:02:27.450 --> 00:02:29.070 proteins put together. 00:02:29.070 --> 00:02:31.250 And inside they have some genetic material, which might 00:02:31.250 --> 00:02:33.700 be DNA or it might be RNA. 00:02:33.700 --> 00:02:35.870 So let me draw their genetic material. 00:02:35.870 --> 00:02:38.420 The protein is not necessarily transparent, but if it was, 00:02:38.420 --> 00:02:42.960 you would see some genetic material inside of there. 00:02:42.960 --> 00:02:48.440 So the question is, is this thing life? 00:02:48.440 --> 00:02:49.580 It seems pretty inanimate. 00:02:49.580 --> 00:02:50.540 It doesn't grow. 00:02:50.540 --> 00:02:51.510 It doesn't change. 00:02:51.510 --> 00:02:53.200 It doesn't metabolize things. 00:02:53.200 --> 00:02:55.200 This thing, left to its own devices, is just 00:02:55.200 --> 00:02:55.850 going to sit there. 00:02:55.850 --> 00:02:59.600 It's just going to sit there the way a book on a table just 00:02:59.600 --> 00:03:00.690 sits there. 00:03:00.690 --> 00:03:02.280 It won't change anything. 00:03:02.280 --> 00:03:06.560 But what happens is, the debate arises. 00:03:06.560 --> 00:03:08.470 I mean you might say, hey Sal, when you define it that way, 00:03:08.470 --> 00:03:10.690 just looks like a bunch of molecules put together. 00:03:10.690 --> 00:03:11.740 That isn't life. 00:03:11.740 --> 00:03:14.350 But it starts to seem like life all of a sudden when it 00:03:14.350 --> 00:03:17.100 comes in contact with the things that we normally 00:03:17.100 --> 00:03:18.220 consider life. 00:03:18.220 --> 00:03:22.480 So what viruses do, the classic example is, a virus 00:03:22.480 --> 00:03:24.680 will attach itself to a cell. 00:03:24.680 --> 00:03:28.590 So let me draw this thing a little bit smaller. 00:03:28.590 --> 00:03:30.260 So let's say that this is my virus. 00:03:30.260 --> 00:03:32.562 I'll draw it as a little hexagon. 00:03:32.562 --> 00:03:34.980 And what it does is, it'll attach itself to a cell. 00:03:34.980 --> 00:03:35.795 And it could be any type of cell. 00:03:35.795 --> 00:03:39.155 It could be a bacteria cell, it could be a plant cell, it 00:03:39.155 --> 00:03:41.190 could be a human cell. 00:03:41.190 --> 00:03:43.820 Let me draw the cell here. 00:03:43.820 --> 00:03:48.540 Cells are usually far larger than the virus. 00:03:48.540 --> 00:03:51.610 In the case of cells that have soft membranes, the virus 00:03:51.610 --> 00:03:53.850 figures out some way to enter it. 00:03:53.850 --> 00:03:58.780 Sometimes it can essentially fuse-- I don't want to 00:03:58.780 --> 00:04:01.390 complicate the issue-- but sometimes viruses have their 00:04:01.390 --> 00:04:02.480 own little membranes. 00:04:02.480 --> 00:04:03.740 And we'll talk about in a second where 00:04:03.740 --> 00:04:04.760 it gets their membranes. 00:04:04.760 --> 00:04:08.270 So a virus might have its own membrane like that. 00:04:08.270 --> 00:04:10.520 That's around its capsid. 00:04:10.520 --> 00:04:13.470 And then these membranes will fuse. 00:04:13.470 --> 00:04:16.785 And then the virus will be able to enter into the cell. 00:04:16.785 --> 00:04:18.000 Now, that's one method. 00:04:18.000 --> 00:04:19.670 And another method, and they're seldom 00:04:19.670 --> 00:04:20.589 all the same way. 00:04:20.589 --> 00:04:24.020 But let's say another method would be, the virus 00:04:24.020 --> 00:04:26.910 convinces-- just based on some protein receptors on it, or 00:04:26.910 --> 00:04:29.810 protein receptors on the cells-- and obviously this has 00:04:29.810 --> 00:04:31.650 to be kind of a Trojan horse type of thing. 00:04:31.650 --> 00:04:33.600 The cell doesn't want viruses. 00:04:33.600 --> 00:04:36.390 So the virus has to somehow convince the cell that it's a 00:04:36.390 --> 00:04:38.050 non-foreign particle. 00:04:38.050 --> 00:04:41.770 We could do hundreds of videos on how viruses work and it's a 00:04:41.770 --> 00:04:43.430 continuing field of research. 00:04:43.430 --> 00:04:47.580 But sometimes you might have a virus that just gets consumed 00:04:47.580 --> 00:04:48.120 by the cell. 00:04:48.120 --> 00:04:49.930 Maybe the cell just thinks it's something that it needs 00:04:49.930 --> 00:04:50.960 to consume. 00:04:50.960 --> 00:04:53.130 So the cell wraps around it like this. 00:04:56.780 --> 00:04:58.930 And these sides will eventually merge. 00:04:58.930 --> 00:05:01.670 And then the cell and the virus will go into it. 00:05:01.670 --> 00:05:03.160 This is called endocytosis. 00:05:03.160 --> 00:05:04.020 I'll just talk about that. 00:05:04.020 --> 00:05:06.640 It just brings it into its cytoplasm. 00:05:06.640 --> 00:05:11.020 It doesn't happen just to viruses. 00:05:11.020 --> 00:05:12.890 But this is one mechanism that can enter. 00:05:12.890 --> 00:05:17.320 And then in cases where the cell in question-- for example 00:05:17.320 --> 00:05:20.280 in the situation with bacteria-- if the cell has a 00:05:20.280 --> 00:05:25.520 very hard shell-- let me do it in a good color. 00:05:25.520 --> 00:05:29.040 So let's say that this is a bacteria right here. 00:05:29.040 --> 00:05:30.510 And it has a hard shell. 00:05:30.510 --> 00:05:32.830 The viruses don't even enter the cell. 00:05:32.830 --> 00:05:36.440 They just hang out outside of the cell like this. 00:05:36.440 --> 00:05:37.740 Not drawing to scale. 00:05:37.740 --> 00:05:40.690 And they actually inject their genetic material. 00:05:40.690 --> 00:05:43.790 So there's obviously a huge-- there's a wide variety of ways 00:05:43.790 --> 00:05:45.680 of how the viruses get into cells. 00:05:45.680 --> 00:05:46.780 But that's beside the point. 00:05:46.780 --> 00:05:49.420 The interesting thing is that they do get into the cell. 00:05:49.420 --> 00:05:52.240 And once they do get into the cell, they release their 00:05:52.240 --> 00:05:54.570 genetic material into the cell. 00:05:54.570 --> 00:05:56.970 So their genetic material will float around. 00:05:56.970 --> 00:06:01.390 If their genetic material is already in the form of RNA-- 00:06:01.390 --> 00:06:05.700 and I could imagine almost every possibility of different 00:06:05.700 --> 00:06:08.160 ways for viruses to work probably do exist in nature. 00:06:08.160 --> 00:06:09.400 We just haven't found them. 00:06:09.400 --> 00:06:11.630 But the ones that we've already found really do kind 00:06:11.630 --> 00:06:13.880 of do it in every possible way. 00:06:13.880 --> 00:06:20.720 So if they have RNA, this RNA can immediately start being 00:06:20.720 --> 00:06:23.170 used to essentially-- let's say this is the 00:06:23.170 --> 00:06:25.540 nucleus of the cell. 00:06:25.540 --> 00:06:28.850 That's the nucleus of the cell and it normally has the DNA in 00:06:28.850 --> 00:06:29.480 it like that. 00:06:29.480 --> 00:06:30.720 Maybe I'll do the DNA in a different color. 00:06:30.720 --> 00:06:37.260 But DNA gets transcribed into RNA, normally. 00:06:37.260 --> 00:06:39.940 So normally, the cell, this a normal working cell, the RNA 00:06:39.940 --> 00:06:43.540 exits the nucleus, it goes to the ribosomes, and then you 00:06:43.540 --> 00:06:46.690 have the RNA in conjunction with the tRNA and it produces 00:06:46.690 --> 00:06:49.260 these proteins. 00:06:49.260 --> 00:06:51.030 The RNA codes for different proteins. 00:06:51.030 --> 00:06:53.670 And I talk about that in a different video. 00:06:53.670 --> 00:06:57.000 So these proteins get formed and eventually, they can form 00:06:57.000 --> 00:06:58.800 the different structures in a cell. 00:06:58.800 --> 00:07:03.190 But what a virus does is it hijacks this process here. 00:07:03.190 --> 00:07:04.490 Hijacks this mechanism. 00:07:04.490 --> 00:07:08.550 This RNA will essentially go and do what the cell's own RNA 00:07:08.550 --> 00:07:09.230 would have done. 00:07:09.230 --> 00:07:11.140 And it starts coding for its own proteins. 00:07:11.140 --> 00:07:12.250 Obviously it's not going to code for 00:07:12.250 --> 00:07:13.260 the same things there. 00:07:13.260 --> 00:07:15.790 And actually some of the first proteins it codes for often 00:07:15.790 --> 00:07:19.670 start killing the DNA and the RNA that might otherwise 00:07:19.670 --> 00:07:20.380 compete with it. 00:07:20.380 --> 00:07:22.390 So it codes its own proteins. 00:07:22.390 --> 00:07:26.860 And then those proteins start making more viral shells. 00:07:26.860 --> 00:07:31.520 So those proteins just start constructing more and more 00:07:31.520 --> 00:07:33.840 viral shells. 00:07:33.840 --> 00:07:36.000 At the same time, this RNA is replicating. 00:07:36.000 --> 00:07:39.730 It's using the cell's own mechanisms. Left to its own 00:07:39.730 --> 00:07:40.820 devices it would just sit there. 00:07:40.820 --> 00:07:43.800 But once it enters into a cell it can use all of the nice 00:07:43.800 --> 00:07:47.000 machinery that a cell has around to replicate itself. 00:07:47.000 --> 00:07:51.360 And it's kind of amazing, just the biochemistry of it. 00:07:51.360 --> 00:07:54.810 That these RNA molecules then find themselves 00:07:54.810 --> 00:07:57.470 back in these capsids. 00:07:57.470 --> 00:08:00.290 And then once there's enough of these and the cell has 00:08:00.290 --> 00:08:05.620 essentially all of its resources have been depleted, 00:08:05.620 --> 00:08:09.990 the viruses, these individual new viruses that have 00:08:09.990 --> 00:08:15.410 replicated themselves using all of the cell's mechanisms, 00:08:15.410 --> 00:08:17.370 will find some way to exit the cell. 00:08:17.370 --> 00:08:20.860 The most-- I don't want to say, typical, because we 00:08:20.860 --> 00:08:23.110 haven't even discovered all the different types of viruses 00:08:23.110 --> 00:08:26.750 there are-- but one that's, I guess, talked about the most, 00:08:26.750 --> 00:08:28.760 is when there's enough of these, they'll release 00:08:28.760 --> 00:08:30.880 proteins or they'll construct proteins. 00:08:30.880 --> 00:08:32.390 Because they don't make their own. 00:08:32.390 --> 00:08:35.860 That essentially cause the cell to either kill itself or 00:08:35.860 --> 00:08:37.140 its membrane to dissolve. 00:08:37.140 --> 00:08:39.260 So the membrane dissolves. 00:08:39.260 --> 00:08:41.480 And essentially the cell lyses. 00:08:41.480 --> 00:08:42.409 Let me write that down. 00:08:42.409 --> 00:08:43.840 The cell lyses. 00:08:43.840 --> 00:08:46.110 And lyses just means that the cell's membrane just 00:08:46.110 --> 00:08:46.900 disappears. 00:08:46.900 --> 00:08:50.480 And then all of these guys can emerge for themselves. 00:08:50.480 --> 00:08:53.470 Now I talked about before that have some of these guys, that 00:08:53.470 --> 00:08:54.750 they have their own membrane. 00:08:54.750 --> 00:08:56.710 So how did they get there, these 00:08:56.710 --> 00:08:58.400 kind of bilipid membranes? 00:08:58.400 --> 00:09:00.900 Well some of them, what they do is, once they replicate 00:09:00.900 --> 00:09:07.380 inside of a cell, they exit maybe not even killing-- they 00:09:07.380 --> 00:09:08.650 don't have to lyse. 00:09:08.650 --> 00:09:11.620 Everything I talk about, these are specific ways that a virus 00:09:11.620 --> 00:09:12.150 might work. 00:09:12.150 --> 00:09:15.630 But viruses really kind of explore-- well different types 00:09:15.630 --> 00:09:17.620 of viruses do almost every different combination you 00:09:17.620 --> 00:09:22.610 could imagine of replicating and coding for proteins and 00:09:22.610 --> 00:09:23.400 escaping from cells. 00:09:23.400 --> 00:09:24.720 Some of them just bud. 00:09:24.720 --> 00:09:26.560 And when they bud, they essentially, you can kind of 00:09:26.560 --> 00:09:28.070 imagine that they push against the cell 00:09:28.070 --> 00:09:29.670 wall, or the membrane. 00:09:29.670 --> 00:09:30.740 I shouldn't say cell wall. 00:09:30.740 --> 00:09:32.630 The cell's outer membrane. 00:09:32.630 --> 00:09:36.130 And then when they push against it, they take some of 00:09:36.130 --> 00:09:38.070 the membrane with them. 00:09:38.070 --> 00:09:41.260 Until eventually the cell will-- when this goes up 00:09:41.260 --> 00:09:43.810 enough, this'll pop together and it'll take some of the 00:09:43.810 --> 00:09:44.565 membrane with it. 00:09:44.565 --> 00:09:47.280 And you could imagine why that would be useful thing 00:09:47.280 --> 00:09:49.030 to have with you. 00:09:49.030 --> 00:09:51.260 Because now that you have this membrane, you kind of look 00:09:51.260 --> 00:09:52.520 like this cell. 00:09:52.520 --> 00:09:55.300 So when you want to go infect another cell like this, you're 00:09:55.300 --> 00:09:58.530 not going to necessarily look like a foreign particle. 00:09:58.530 --> 00:10:02.780 So it's a very useful way to look like something that 00:10:02.780 --> 00:10:03.470 you're not. 00:10:03.470 --> 00:10:06.940 And if you don't think that this is creepy-crawly enough, 00:10:06.940 --> 00:10:10.780 that you're hijacking the DNA of an organism, viruses can 00:10:10.780 --> 00:10:14.740 actually change the DNA an organism. 00:10:14.740 --> 00:10:18.830 And actually one of the most common examples is HIV virus. 00:10:18.830 --> 00:10:21.480 Let me write that down. 00:10:21.480 --> 00:10:27.480 HIV, which is a type of retrovirus, which is 00:10:27.480 --> 00:10:28.280 fascinating. 00:10:28.280 --> 00:10:31.930 Because what they do is, so they have RNA in them. 00:10:35.810 --> 00:10:38.030 And when they enter into a cell, let's say that they got 00:10:38.030 --> 00:10:39.430 into the cell. 00:10:39.430 --> 00:10:42.950 So it's inside of the cell like this. 00:10:42.950 --> 00:10:46.570 They actually bring along with them a protein. 00:10:46.570 --> 00:10:49.600 And every time you say, where do they get this protein? 00:10:49.600 --> 00:10:51.390 All of this stuff came from a different cell. 00:10:51.390 --> 00:10:54.490 They use some other cell's amino acids and ribosomes and 00:10:54.490 --> 00:10:56.800 nucleic acids and everything to build themselves. 00:10:56.800 --> 00:10:58.780 So any proteins that they have in them came 00:10:58.780 --> 00:11:00.080 from another cell. 00:11:00.080 --> 00:11:04.610 But they bring with them, this protein reverse transcriptase. 00:11:04.610 --> 00:11:07.850 And the reverse transcriptase takes their RNA and 00:11:07.850 --> 00:11:11.490 codes it into DNA. 00:11:11.490 --> 00:11:14.790 So its RNA to DNA. 00:11:14.790 --> 00:11:16.810 Which when it was first discovered was, kind of, 00:11:16.810 --> 00:11:19.950 people always thought that you always went from DNA to RNA, 00:11:19.950 --> 00:11:22.110 but this kind of broke that paradigm. 00:11:22.110 --> 00:11:23.850 But it codes from RNA to DNA. 00:11:23.850 --> 00:11:29.020 And if that's not bad enough, it'll incorporate that DNA 00:11:29.020 --> 00:11:31.350 into the DNA of the host cell. 00:11:31.350 --> 00:11:34.500 So that DNA will incorporate itself into the 00:11:34.500 --> 00:11:35.200 DNA of the host cell. 00:11:35.200 --> 00:11:37.690 Let's say the yellow is the DNA of the host cell. 00:11:37.690 --> 00:11:41.000 And this is its nucleus. 00:11:41.000 --> 00:11:44.070 So it actually messes with the genetic makeup 00:11:44.070 --> 00:11:46.030 of what it's infecting. 00:11:46.030 --> 00:11:51.570 And when I made the videos on bacteria I said, hey for every 00:11:51.570 --> 00:11:53.790 one human cell we have twenty bacteria cells. 00:11:53.790 --> 00:11:56.420 And they live with us and they're useful and they're 00:11:56.420 --> 00:12:00.100 part of us and they're 10% of our dry mass and all of that. 00:12:00.100 --> 00:12:02.170 But bacteria are kind of along for the ride. 00:12:02.170 --> 00:12:03.860 They don't change who we are. 00:12:03.860 --> 00:12:07.010 But these retroviruses, they're actually changing our 00:12:07.010 --> 00:12:07.940 genetic makeup. 00:12:07.940 --> 00:12:10.650 I mean, my genes, I take very personally. 00:12:10.650 --> 00:12:12.380 They define who I am. 00:12:12.380 --> 00:12:14.630 But these guys will actually go in and 00:12:14.630 --> 00:12:16.240 change my genetic makeup. 00:12:16.240 --> 00:12:19.300 And then once they're part of the DNA, then just the natural 00:12:19.300 --> 00:12:25.330 DNA to RNA to protein process will code 00:12:25.330 --> 00:12:27.180 their actual proteins. 00:12:27.180 --> 00:12:30.160 Or their-- what they need to-- so sometimes they'll lay 00:12:30.160 --> 00:12:31.420 dormant and do nothing. 00:12:31.420 --> 00:12:33.730 And sometimes-- let's say sometimes in some type of 00:12:33.730 --> 00:12:35.790 environmental trigger, they'll start coding 00:12:35.790 --> 00:12:37.110 for themselves again. 00:12:37.110 --> 00:12:38.620 And they'll start producing more. 00:12:38.620 --> 00:12:41.980 But they're producing it directly from the organism's 00:12:41.980 --> 00:12:43.110 cell's DNA. 00:12:43.110 --> 00:12:45.120 They become part of the organism. 00:12:45.120 --> 00:12:49.280 I mean I can't imagine a more intimate way to become part of 00:12:49.280 --> 00:12:51.530 an organism than to become part of its DNA. 00:12:51.530 --> 00:12:52.870 I can't imagine any other way to 00:12:52.870 --> 00:12:55.680 actually define an organism. 00:12:55.680 --> 00:13:00.910 And if this by itself is not eerie enough, and just so you 00:13:00.910 --> 00:13:06.770 know, this notion right here, when a virus becomes part of 00:13:06.770 --> 00:13:09.430 an organism's DNA, this is called a provirus. 00:13:13.180 --> 00:13:16.890 But if this isn't eerie enough, they estimate-- so if 00:13:16.890 --> 00:13:23.500 this infects a cell in my nose or in my arm, as this cell 00:13:23.500 --> 00:13:27.250 experiences mitosis, all of its offspring-- but its 00:13:27.250 --> 00:13:29.030 offspring are genetically identical-- are going to have 00:13:29.030 --> 00:13:30.600 this viral DNA. 00:13:30.600 --> 00:13:32.060 And that might be fine, but at least my 00:13:32.060 --> 00:13:33.120 children won't get it. 00:13:33.120 --> 00:13:35.980 You know, at least it won't become part of my species. 00:13:35.980 --> 00:13:38.710 But it doesn't have to just infect somatic cells, it could 00:13:38.710 --> 00:13:41.170 infect a germ cell. 00:13:41.170 --> 00:13:44.510 So it could go into a germ cell. 00:13:44.510 --> 00:13:46.850 And the germ cells, we've learned already, these are the 00:13:46.850 --> 00:13:49.380 ones that produce gametes. 00:13:49.380 --> 00:13:52.930 For men, that's sperm and for women it's eggs. 00:13:52.930 --> 00:13:55.180 But you could imagine, once you've infected a germ cell, 00:13:55.180 --> 00:13:59.010 once you become part of a germ cell's DNA, then I'm passing 00:13:59.010 --> 00:14:02.600 on that viral DNA to my son or my daughter. 00:14:02.600 --> 00:14:05.540 And they are going to pass it on to their children. 00:14:05.540 --> 00:14:10.260 And just that idea by itself is, at least to my mind. 00:14:10.260 --> 00:14:12.130 vaguely creepy. 00:14:12.130 --> 00:14:16.050 And people estimate that 5-8%-- and this kind of really 00:14:16.050 --> 00:14:19.480 blurs, it makes you think about what we as humans really 00:14:19.480 --> 00:14:26.800 are-- but the estimate is 5-8% of the human genome-- so when 00:14:26.800 --> 00:14:29.500 I talked about bacteria I just talked about things that were 00:14:29.500 --> 00:14:30.850 along for the ride. 00:14:30.850 --> 00:14:33.240 But the current estimate, and I looked up this a lot. 00:14:33.240 --> 00:14:35.210 I found 8% someplace, 5% someplace. 00:14:35.210 --> 00:14:35.990 It's all a guess. 00:14:35.990 --> 00:14:37.650 I mean people are doing it based on just looking at the 00:14:37.650 --> 00:14:40.690 DNA and how similar it is to DNA in other organisms. But 00:14:40.690 --> 00:14:47.390 the estimate is 5-8% of the human genome is from viruses, 00:14:47.390 --> 00:14:51.760 is from ancient retroviruses that incorporated themselves 00:14:51.760 --> 00:14:53.530 into the human germ line. 00:14:53.530 --> 00:14:55.725 So into the human DNA. 00:14:55.725 --> 00:14:57.860 So these are called endogenous retroviruses. 00:15:04.800 --> 00:15:07.150 Which is mind blowing to me, because it's not just saying 00:15:07.150 --> 00:15:09.290 these things are along for the ride or that they might help 00:15:09.290 --> 00:15:10.070 us or hurt us. 00:15:10.070 --> 00:15:14.000 It's saying that we are-- 5-8% of our DNA 00:15:14.000 --> 00:15:16.390 actually comes from viruses. 00:15:16.390 --> 00:15:17.850 And this is another thing that speaks to 00:15:17.850 --> 00:15:19.720 just genetic variation. 00:15:19.720 --> 00:15:24.210 Because viruses do something-- I mean this is called 00:15:24.210 --> 00:15:27.760 horizontal transfer of DNA. 00:15:27.760 --> 00:15:30.480 And you could imagine, as a virus goes from one species to 00:15:30.480 --> 00:15:37.220 the next, as it goes from Species A to B, if it mutates 00:15:37.220 --> 00:15:41.310 to be able to infiltrate these cells, it might take some-- 00:15:41.310 --> 00:15:43.810 it'll take the DNA that it already has, that 00:15:43.810 --> 00:15:45.490 makes it, it with it. 00:15:45.490 --> 00:15:48.180 But sometimes, when it starts coding for some of these other 00:15:48.180 --> 00:15:52.830 guys, so let's say that this is a provirus right here. 00:15:52.830 --> 00:15:55.860 Where the blue part is the original virus. 00:15:55.860 --> 00:16:00.960 The yellow is the organism's historic DNA. 00:16:00.960 --> 00:16:04.230 Sometimes when it codes, it takes up little sections of 00:16:04.230 --> 00:16:07.200 the other organism's DNA. 00:16:07.200 --> 00:16:11.810 So maybe most of it was the viral DNA, but it might have, 00:16:11.810 --> 00:16:14.070 when it transcribed and translated itself, it might 00:16:14.070 --> 00:16:16.710 have taken a little bit-- or at least when it translated or 00:16:16.710 --> 00:16:18.460 replicated itself-- it might take a little bit of the 00:16:18.460 --> 00:16:20.540 organism's previous DNA. 00:16:20.540 --> 00:16:23.690 So it's actually cutting parts of DNA from one organism and 00:16:23.690 --> 00:16:24.950 bringing it to another organism. 00:16:24.950 --> 00:16:27.490 Taking it from one member of a species to another member of 00:16:27.490 --> 00:16:27.810 the species. 00:16:27.810 --> 00:16:29.750 But it can definitely go cross-species. 00:16:29.750 --> 00:16:32.860 So you have this idea all of a sudden that DNA can jump 00:16:32.860 --> 00:16:34.090 between species. 00:16:34.090 --> 00:16:36.410 It really kind of-- I don't know, for me it makes me 00:16:36.410 --> 00:16:39.930 appreciate how interconnected-- as a species, 00:16:39.930 --> 00:16:41.950 we kind of imagine that we're by ourselves and can only 00:16:41.950 --> 00:16:45.110 reproduce with each other and have genetic variation within 00:16:45.110 --> 00:16:45.860 a population. 00:16:45.860 --> 00:16:50.190 But viruses introduce this notion of horizontal transfer 00:16:50.190 --> 00:16:53.090 via transduction. 00:16:53.090 --> 00:16:57.640 Horizontal transduction is just the idea of, look when I 00:16:57.640 --> 00:17:00.660 replicate this virus, I might take a little bit of the 00:17:00.660 --> 00:17:04.349 organism that I'm freeloading off of, I might take a little 00:17:04.349 --> 00:17:06.010 bit of their DNA with me. 00:17:06.010 --> 00:17:09.160 And infect that DNA into the next organism. 00:17:09.160 --> 00:17:11.329 So you actually have this DNA, this jumping, 00:17:11.329 --> 00:17:13.119 from organism to organism. 00:17:13.119 --> 00:17:17.300 So it kind of unifies all DNA-based life. 00:17:17.300 --> 00:17:20.609 Which is all the life that we know on the planet. 00:17:20.609 --> 00:17:24.900 And if all of this isn't creepy enough-- and actually 00:17:24.900 --> 00:17:28.540 maybe I'll save the creepiest part for the end. 00:17:28.540 --> 00:17:30.800 But there's a whole-- we could talk all about the different 00:17:30.800 --> 00:17:31.670 classes of viruses. 00:17:31.670 --> 00:17:33.810 But just so you're familiar with some of the terminology, 00:17:33.810 --> 00:17:37.895 when a virus attacks bacteria, which they often do. 00:17:37.895 --> 00:17:41.150 And we study these the most because this might be a good 00:17:41.150 --> 00:17:42.630 alternative to antibiotics. 00:17:42.630 --> 00:17:45.430 Because viruses that attack bacteria might-- sometimes the 00:17:45.430 --> 00:17:47.820 bacteria is far worse for the virus-- but these are called 00:17:47.820 --> 00:17:49.070 bacteriaphages. 00:17:52.610 --> 00:17:55.320 And I've already talked to you about how they have their DNA. 00:17:55.320 --> 00:17:57.890 But since bacteria have hard walls, they will just inject 00:17:57.890 --> 00:18:00.940 the DNA inside of the bacteria. 00:18:00.940 --> 00:18:06.630 And when you talk about DNA, this idea of a provirus. 00:18:06.630 --> 00:18:09.170 So when a virus lyses it like this, this is 00:18:09.170 --> 00:18:11.090 called the lytic cycle. 00:18:11.090 --> 00:18:13.760 This is just some terminology that's good to know if you're 00:18:13.760 --> 00:18:16.250 going to take a biology exam about this stuff. 00:18:16.250 --> 00:18:18.600 And when the virus incorporates it into the DNA 00:18:18.600 --> 00:18:22.350 and lays dormant, incorporates into the DNA of the host 00:18:22.350 --> 00:18:25.420 organism and lays dormant for awhile, this is called the 00:18:25.420 --> 00:18:28.030 lysogenic cycle. 00:18:28.030 --> 00:18:32.030 And normally, a provirus is essentially experiencing a 00:18:32.030 --> 00:18:35.910 lysogenic cycle in eurkaryotes, in organisms that 00:18:35.910 --> 00:18:38.250 have a nuclear membrane. 00:18:38.250 --> 00:18:40.890 Normally when people talk about the lysogenic cycle, 00:18:40.890 --> 00:18:44.750 they're talking about viral DNA laying dormant in the DNA 00:18:44.750 --> 00:18:45.600 of bacteria. 00:18:45.600 --> 00:18:48.600 Or bacteriophage DNA laying dormant 00:18:48.600 --> 00:18:51.050 in the DNA of bacteria. 00:18:51.050 --> 00:18:53.380 But just to kind of give you an idea of what this, quote 00:18:53.380 --> 00:18:59.480 unquote, looks like, right here. 00:18:59.480 --> 00:19:01.550 I got these two pictures from Wikipedia. 00:19:01.550 --> 00:19:02.800 One is from the CDC. 00:19:11.360 --> 00:19:14.200 These little green dots you see right here all over the 00:19:14.200 --> 00:19:17.540 surface, this big thing you see here, this is a white 00:19:17.540 --> 00:19:20.330 blood cell. 00:19:20.330 --> 00:19:21.760 Part of the human immune system. 00:19:21.760 --> 00:19:23.050 This is a white blood cell. 00:19:27.540 --> 00:19:31.060 And what you see emerging from the surface, essentially 00:19:31.060 --> 00:19:34.510 budding from the surface of this white blood cell-- and 00:19:34.510 --> 00:19:36.300 this gives you a sense of scale too-- 00:19:36.300 --> 00:19:39.700 these are HIV-1 viruses. 00:19:39.700 --> 00:19:46.970 And so you're familiar with the terminology, the HIV is a 00:19:46.970 --> 00:19:51.810 virus that infects white blood cells. 00:19:51.810 --> 00:19:54.890 AIDS is the syndrome you get once your immune system is 00:19:54.890 --> 00:19:55.900 weakened to the point. 00:19:55.900 --> 00:19:58.860 And then many people suffer infections that people with a 00:19:58.860 --> 00:20:01.450 strong immune system normally won't suffer from. 00:20:01.450 --> 00:20:03.050 But this is creepy. 00:20:03.050 --> 00:20:06.360 These things went inside this huge cell, they used the 00:20:06.360 --> 00:20:11.555 cell's own mechanism to reproduce its own DNA or its 00:20:11.555 --> 00:20:14.300 own RNA and these protein capsids. 00:20:14.300 --> 00:20:16.270 And then they bud from the cell and take a little bit of 00:20:16.270 --> 00:20:17.490 the membrane with it. 00:20:17.490 --> 00:20:20.990 And they can even leave some of their DNA behind in this 00:20:20.990 --> 00:20:22.340 cell's own DNA. 00:20:22.340 --> 00:20:25.280 So they really change what the cell is all about. 00:20:25.280 --> 00:20:26.890 This is another creepy picture. 00:20:26.890 --> 00:20:28.140 These are bacteriaphages. 00:20:34.500 --> 00:20:36.110 And these show you what I said before. 00:20:36.110 --> 00:20:38.450 This is a bacteria right here. 00:20:38.450 --> 00:20:41.360 This is its cell wall. 00:20:41.360 --> 00:20:42.100 And it's hard. 00:20:42.100 --> 00:20:45.020 So it's hard to just emerge into it. 00:20:45.020 --> 00:20:47.040 Or you can't just merge, fuse membranes with it. 00:20:47.040 --> 00:20:52.290 So they hang out on the outside of this bacteria. 00:20:52.290 --> 00:20:55.410 And they are essentially injecting their genetic 00:20:55.410 --> 00:20:58.280 material into the bacteria itself. 00:20:58.280 --> 00:20:59.890 And you could imagine, just looking at the 00:20:59.890 --> 00:21:01.000 size of these things. 00:21:01.000 --> 00:21:02.090 I mean, this is a cell. 00:21:02.090 --> 00:21:04.350 And it looks like a whole planet or something. 00:21:04.350 --> 00:21:05.650 Or this is a bacteria and these 00:21:05.650 --> 00:21:06.620 things are so much smaller. 00:21:06.620 --> 00:21:08.170 Roughly 1/100 of a bacteria. 00:21:08.170 --> 00:21:10.570 And these are much less than 1/100 of this cell we're 00:21:10.570 --> 00:21:11.110 talking about. 00:21:11.110 --> 00:21:15.510 And they're extremely hard to filter for. 00:21:15.510 --> 00:21:16.520 To kind of keep out. 00:21:16.520 --> 00:21:20.780 Because they are such, such small particles. 00:21:20.780 --> 00:21:23.290 If you think that these are exotic things that exist for 00:21:23.290 --> 00:21:31.360 things like HIV or Ebola , which they do cause, or SARS, 00:21:31.360 --> 00:21:32.340 you're right. 00:21:32.340 --> 00:21:33.730 But they're also common things. 00:21:33.730 --> 00:21:35.490 I mean, I said at the beginning of this video that I 00:21:35.490 --> 00:21:36.300 have a cold. 00:21:36.300 --> 00:21:40.040 And I have a cold because some viruses have infected the 00:21:40.040 --> 00:21:42.610 tissue in my nasal passage. 00:21:42.610 --> 00:21:46.190 And they're causing me to have a runny nose and whatnot. 00:21:46.190 --> 00:21:48.540 And viruses also cause the chicken pox. 00:21:48.540 --> 00:21:50.550 They cause the herpes simplex virus. 00:21:50.550 --> 00:21:51.540 Causes cold sores. 00:21:51.540 --> 00:21:53.430 So they're with us all around. 00:21:53.430 --> 00:21:56.000 I can almost guarantee you have some virus 00:21:56.000 --> 00:21:57.740 with you as you speak. 00:21:57.740 --> 00:21:58.630 They're all around you. 00:21:58.630 --> 00:22:04.320 But it's a very 00:22:04.320 --> 00:22:06.480 philosophically puzzling question. 00:22:06.480 --> 00:22:09.090 Because I started with, at the beginning, are these life? 00:22:09.090 --> 00:22:11.495 And at first when I just showed it to you, look they 00:22:11.495 --> 00:22:13.740 are just this protein with some nucleic 00:22:13.740 --> 00:22:15.280 acid molecule in it. 00:22:15.280 --> 00:22:16.340 And it's not doing anything. 00:22:16.340 --> 00:22:17.780 And that doesn't look like life to me. 00:22:17.780 --> 00:22:18.610 It's not moving around. 00:22:18.610 --> 00:22:19.660 It doesn't have a metabolism. 00:22:19.660 --> 00:22:20.390 It's not eating. 00:22:20.390 --> 00:22:21.560 It's not reproducing. 00:22:21.560 --> 00:22:23.120 But then all of a sudden, when you think about what it's 00:22:23.120 --> 00:22:27.130 doing to cells and how it uses cells to kind of reproduce. 00:22:27.130 --> 00:22:29.700 It kind of like-- in business terms it's asset light. 00:22:29.700 --> 00:22:31.920 It doesn't need all of the machinery because it can use 00:22:31.920 --> 00:22:35.850 other people's machinery to replicate itself. 00:22:35.850 --> 00:22:38.080 You almost kind of want to view it as a 00:22:38.080 --> 00:22:39.520 smarter form of life. 00:22:39.520 --> 00:22:42.480 Because it doesn't go through all of the trouble of what 00:22:42.480 --> 00:22:44.110 every other form of life has. 00:22:44.110 --> 00:22:47.570 It makes you question what life is, or even what we are. 00:22:47.570 --> 00:22:51.510 Are we these things that contain DNA or are we just 00:22:51.510 --> 00:22:54.170 transport mechanisms for the DNA? 00:22:54.170 --> 00:22:56.260 And these are kind of the more important things. 00:22:56.260 --> 00:22:59.710 And these viral infections are just battles between different 00:22:59.710 --> 00:23:02.340 forms of DNA and RNA and whatnot. 00:23:02.340 --> 00:23:04.330 Anyway I don't want to get too philosophical on you. 00:23:04.330 --> 00:23:08.840 But hopefully this gives you a good idea of what viruses are 00:23:08.840 --> 00:23:12.940 and why they really are, in my mind, the most fascinating 00:23:12.940 --> 00:23:15.870 pseudo organism in all of biology.