0:00:00.470,0:00:03.210 Considering that I have a cold[br]right now, I can't imagine a 0:00:03.210,0:00:08.109 more appropriate topic to make[br]a video on than a virus. 0:00:08.109,0:00:09.930 And I didn't want to[br]make it that thick. 0:00:09.930,0:00:11.380 A virus, or viruses. 0:00:14.760,0:00:19.080 And in my opinion, viruses are,[br]on some level, the most 0:00:19.080,0:00:21.450 fascinating thing in[br]all of biology. 0:00:21.450,0:00:25.560 Because they really blur the[br]boundary between what is an 0:00:25.560,0:00:27.440 inanimate object and[br]what is life? 0:00:30.080,0:00:33.410 I mean if we look at ourselves,[br]or life as one of 0:00:33.410,0:00:35.210 those things that you know[br]it when you see it. 0:00:35.210,0:00:39.300 If you see something that,[br]it's born, it grows, it's 0:00:39.300,0:00:40.460 constantly changing. 0:00:40.460,0:00:41.510 Maybe it moves around. 0:00:41.510,0:00:42.260 Maybe it doesn't. 0:00:42.260,0:00:44.400 But it's metabolizing things[br]around itself. 0:00:44.400,0:00:46.310 It reproduces and[br]then it dies. 0:00:46.310,0:00:48.300 You say, hey, that's[br]probably life. 0:00:48.300,0:00:50.960 And in this, we throw most[br]things that we see-- or we 0:00:50.960,0:00:52.815 throw in, us. 0:00:52.815,0:00:55.360 We throw in bacteria. 0:00:55.360,0:00:57.120 We throw in plants. 0:00:57.120,0:01:00.830 I mean, I could-- I'm kind of[br]butchering the taxonomy system 0:01:00.830,0:01:03.275 here, but we tend to know[br]life when we see it. 0:01:03.275,0:01:07.480 But all viruses are, they're[br]just a bunch of genetic 0:01:07.480,0:01:09.740 information inside[br]of a protein. 0:01:09.740,0:01:11.230 Inside of a protein capsule. 0:01:11.230,0:01:13.490 So let me draw. 0:01:13.490,0:01:16.340 And the genetic information[br]can come in any form. 0:01:16.340,0:01:22.240 So it can be an RNA, it could[br]be DNA, it could be 0:01:22.240,0:01:24.670 single-stranded RNA,[br]double-stranded RNA. 0:01:24.670,0:01:27.260 Sometimes for single stranded[br]they'll write these two little 0:01:27.260,0:01:29.250 S's in front of it. 0:01:29.250,0:01:30.950 Let's say they are talking about[br]double stranded DNA, 0:01:30.950,0:01:32.910 they'll put a ds[br]in front of it. 0:01:32.910,0:01:35.330 But the general idea-- and[br]viruses can come in all of 0:01:35.330,0:01:38.110 these forms-- is that they have[br]some genetic information, 0:01:38.110,0:01:40.530 some chain of nucleic acids. 0:01:40.530,0:01:43.730 Either as single or double[br]stranded RNA or single or 0:01:43.730,0:01:44.560 double stranded DNA. 0:01:44.560,0:01:47.970 And it's just contained inside[br]some type of protein 0:01:47.970,0:01:49.880 structure, which is[br]called the capsid. 0:01:49.880,0:01:53.240 And kind of the classic[br]drawing is kind of an 0:01:53.240,0:01:56.650 icosahedron type[br]looking thing. 0:01:56.650,0:01:58.200 Let me see if I can[br]do justice to it. 0:01:58.200,0:02:00.610 It looks something like this. 0:02:00.610,0:02:02.800 And not all viruses have to[br]look exactly like this. 0:02:02.800,0:02:05.160 There's thousands of[br]types of viruses. 0:02:05.160,0:02:06.850 And we're really just scratching[br]the surface and 0:02:06.850,0:02:09.630 understanding even what viruses[br]are out there and all 0:02:09.630,0:02:14.800 of the different ways that they[br]can essentially replicate 0:02:14.800,0:02:15.220 themselves. 0:02:15.220,0:02:16.620 We'll talk more about[br]that in the future. 0:02:16.620,0:02:19.110 And I would suspect that pretty[br]much any possible way 0:02:19.110,0:02:21.530 of replication probably[br]does somehow exist 0:02:21.530,0:02:22.750 in the virus world. 0:02:22.750,0:02:25.260 But they really are just these[br]proteins, these protein 0:02:25.260,0:02:27.450 capsids, are just made up[br]of a bunch of little 0:02:27.450,0:02:29.070 proteins put together. 0:02:29.070,0:02:31.250 And inside they have some[br]genetic material, which might 0:02:31.250,0:02:33.700 be DNA or it might be RNA. 0:02:33.700,0:02:35.870 So let me draw their[br]genetic material. 0:02:35.870,0:02:38.420 The protein is not necessarily[br]transparent, but if it was, 0:02:38.420,0:02:42.960 you would see some genetic[br]material inside of there. 0:02:42.960,0:02:48.440 So the question is, is[br]this thing life? 0:02:48.440,0:02:49.580 It seems pretty inanimate. 0:02:49.580,0:02:50.540 It doesn't grow. 0:02:50.540,0:02:51.510 It doesn't change. 0:02:51.510,0:02:53.200 It doesn't metabolize things. 0:02:53.200,0:02:55.200 This thing, left to its[br]own devices, is just 0:02:55.200,0:02:55.850 going to sit there. 0:02:55.850,0:02:59.600 It's just going to sit there the[br]way a book on a table just 0:02:59.600,0:03:00.690 sits there. 0:03:00.690,0:03:02.280 It won't change anything. 0:03:02.280,0:03:06.560 But what happens is,[br]the debate arises. 0:03:06.560,0:03:08.470 I mean you might say, hey Sal,[br]when you define it that way, 0:03:08.470,0:03:10.690 just looks like a bunch of[br]molecules put together. 0:03:10.690,0:03:11.740 That isn't life. 0:03:11.740,0:03:14.350 But it starts to seem like life[br]all of a sudden when it 0:03:14.350,0:03:17.100 comes in contact with the[br]things that we normally 0:03:17.100,0:03:18.220 consider life. 0:03:18.220,0:03:22.480 So what viruses do, the classic[br]example is, a virus 0:03:22.480,0:03:24.680 will attach itself to a cell. 0:03:24.680,0:03:28.590 So let me draw this thing[br]a little bit smaller. 0:03:28.590,0:03:30.260 So let's say that this[br]is my virus. 0:03:30.260,0:03:32.562 I'll draw it as a[br]little hexagon. 0:03:32.562,0:03:34.980 And what it does is, it'll[br]attach itself to a cell. 0:03:34.980,0:03:35.795 And it could be any[br]type of cell. 0:03:35.795,0:03:39.155 It could be a bacteria cell, it[br]could be a plant cell, it 0:03:39.155,0:03:41.190 could be a human cell. 0:03:41.190,0:03:43.820 Let me draw the cell here. 0:03:43.820,0:03:48.540 Cells are usually far larger[br]than the virus. 0:03:48.540,0:03:51.610 In the case of cells that have[br]soft membranes, the virus 0:03:51.610,0:03:53.850 figures out some way[br]to enter it. 0:03:53.850,0:03:58.780 Sometimes it can essentially[br]fuse-- I don't want to 0:03:58.780,0:04:01.390 complicate the issue-- but[br]sometimes viruses have their 0:04:01.390,0:04:02.480 own little membranes. 0:04:02.480,0:04:03.740 And we'll talk about[br]in a second where 0:04:03.740,0:04:04.760 it gets their membranes. 0:04:04.760,0:04:08.270 So a virus might have its[br]own membrane like that. 0:04:08.270,0:04:10.520 That's around its capsid. 0:04:10.520,0:04:13.470 And then these membranes[br]will fuse. 0:04:13.470,0:04:16.785 And then the virus will be able[br]to enter into the cell. 0:04:16.785,0:04:18.000 Now, that's one method. 0:04:18.000,0:04:19.670 And another method,[br]and they're seldom 0:04:19.670,0:04:20.589 all the same way. 0:04:20.589,0:04:24.020 But let's say another method[br]would be, the virus 0:04:24.020,0:04:26.910 convinces-- just based on some[br]protein receptors on it, or 0:04:26.910,0:04:29.810 protein receptors on the cells--[br]and obviously this has 0:04:29.810,0:04:31.650 to be kind of a Trojan[br]horse type of thing. 0:04:31.650,0:04:33.600 The cell doesn't want viruses. 0:04:33.600,0:04:36.390 So the virus has to somehow[br]convince the cell that it's a 0:04:36.390,0:04:38.050 non-foreign particle. 0:04:38.050,0:04:41.770 We could do hundreds of videos[br]on how viruses work and it's a 0:04:41.770,0:04:43.430 continuing field of research. 0:04:43.430,0:04:47.580 But sometimes you might have a[br]virus that just gets consumed 0:04:47.580,0:04:48.120 by the cell. 0:04:48.120,0:04:49.930 Maybe the cell just thinks it's[br]something that it needs 0:04:49.930,0:04:50.960 to consume. 0:04:50.960,0:04:53.130 So the cell wraps around[br]it like this. 0:04:56.780,0:04:58.930 And these sides will[br]eventually merge. 0:04:58.930,0:05:01.670 And then the cell and the[br]virus will go into it. 0:05:01.670,0:05:03.160 This is called endocytosis. 0:05:03.160,0:05:04.020 I'll just talk about that. 0:05:04.020,0:05:06.640 It just brings it into[br]its cytoplasm. 0:05:06.640,0:05:11.020 It doesn't happen[br]just to viruses. 0:05:11.020,0:05:12.890 But this is one mechanism[br]that can enter. 0:05:12.890,0:05:17.320 And then in cases where the cell[br]in question-- for example 0:05:17.320,0:05:20.280 in the situation with bacteria--[br]if the cell has a 0:05:20.280,0:05:25.520 very hard shell-- let me[br]do it in a good color. 0:05:25.520,0:05:29.040 So let's say that this is[br]a bacteria right here. 0:05:29.040,0:05:30.510 And it has a hard shell. 0:05:30.510,0:05:32.830 The viruses don't even[br]enter the cell. 0:05:32.830,0:05:36.440 They just hang out outside[br]of the cell like this. 0:05:36.440,0:05:37.740 Not drawing to scale. 0:05:37.740,0:05:40.690 And they actually inject[br]their genetic material. 0:05:40.690,0:05:43.790 So there's obviously a huge--[br]there's a wide variety of ways 0:05:43.790,0:05:45.680 of how the viruses[br]get into cells. 0:05:45.680,0:05:46.780 But that's beside the point. 0:05:46.780,0:05:49.420 The interesting thing is that[br]they do get into the cell. 0:05:49.420,0:05:52.240 And once they do get into the[br]cell, they release their 0:05:52.240,0:05:54.570 genetic material[br]into the cell. 0:05:54.570,0:05:56.970 So their genetic material[br]will float around. 0:05:56.970,0:06:01.390 If their genetic material is[br]already in the form of RNA-- 0:06:01.390,0:06:05.700 and I could imagine almost every[br]possibility of different 0:06:05.700,0:06:08.160 ways for viruses to work[br]probably do exist in nature. 0:06:08.160,0:06:09.400 We just haven't found them. 0:06:09.400,0:06:11.630 But the ones that we've already[br]found really do kind 0:06:11.630,0:06:13.880 of do it in every[br]possible way. 0:06:13.880,0:06:20.720 So if they have RNA, this RNA[br]can immediately start being 0:06:20.720,0:06:23.170 used to essentially-- let's[br]say this is the 0:06:23.170,0:06:25.540 nucleus of the cell. 0:06:25.540,0:06:28.850 That's the nucleus of the cell[br]and it normally has the DNA in 0:06:28.850,0:06:29.480 it like that. 0:06:29.480,0:06:30.720 Maybe I'll do the DNA in[br]a different color. 0:06:30.720,0:06:37.260 But DNA gets transcribed[br]into RNA, normally. 0:06:37.260,0:06:39.940 So normally, the cell, this a[br]normal working cell, the RNA 0:06:39.940,0:06:43.540 exits the nucleus, it goes to[br]the ribosomes, and then you 0:06:43.540,0:06:46.690 have the RNA in conjunction with[br]the tRNA and it produces 0:06:46.690,0:06:49.260 these proteins. 0:06:49.260,0:06:51.030 The RNA codes for different[br]proteins. 0:06:51.030,0:06:53.670 And I talk about that in[br]a different video. 0:06:53.670,0:06:57.000 So these proteins get formed and[br]eventually, they can form 0:06:57.000,0:06:58.800 the different structures[br]in a cell. 0:06:58.800,0:07:03.190 But what a virus does is it[br]hijacks this process here. 0:07:03.190,0:07:04.490 Hijacks this mechanism. 0:07:04.490,0:07:08.550 This RNA will essentially go and[br]do what the cell's own RNA 0:07:08.550,0:07:09.230 would have done. 0:07:09.230,0:07:11.140 And it starts coding for[br]its own proteins. 0:07:11.140,0:07:12.250 Obviously it's not[br]going to code for 0:07:12.250,0:07:13.260 the same things there. 0:07:13.260,0:07:15.790 And actually some of the first[br]proteins it codes for often 0:07:15.790,0:07:19.670 start killing the DNA and the[br]RNA that might otherwise 0:07:19.670,0:07:20.380 compete with it. 0:07:20.380,0:07:22.390 So it codes its own proteins. 0:07:22.390,0:07:26.860 And then those proteins start[br]making more viral shells. 0:07:26.860,0:07:31.520 So those proteins just start[br]constructing more and more 0:07:31.520,0:07:33.840 viral shells. 0:07:33.840,0:07:36.000 At the same time, this[br]RNA is replicating. 0:07:36.000,0:07:39.730 It's using the cell's own[br]mechanisms. Left to its own 0:07:39.730,0:07:40.820 devices it would[br]just sit there. 0:07:40.820,0:07:43.800 But once it enters into a cell[br]it can use all of the nice 0:07:43.800,0:07:47.000 machinery that a cell has around[br]to replicate itself. 0:07:47.000,0:07:51.360 And it's kind of amazing, just[br]the biochemistry of it. 0:07:51.360,0:07:54.810 That these RNA molecules[br]then find themselves 0:07:54.810,0:07:57.470 back in these capsids. 0:07:57.470,0:08:00.290 And then once there's enough[br]of these and the cell has 0:08:00.290,0:08:05.620 essentially all of its resources[br]have been depleted, 0:08:05.620,0:08:09.990 the viruses, these individual[br]new viruses that have 0:08:09.990,0:08:15.410 replicated themselves using all[br]of the cell's mechanisms, 0:08:15.410,0:08:17.370 will find some way[br]to exit the cell. 0:08:17.370,0:08:20.860 The most-- I don't want to[br]say, typical, because we 0:08:20.860,0:08:23.110 haven't even discovered all the[br]different types of viruses 0:08:23.110,0:08:26.750 there are-- but one that's, I[br]guess, talked about the most, 0:08:26.750,0:08:28.760 is when there's enough of[br]these, they'll release 0:08:28.760,0:08:30.880 proteins or they'll construct[br]proteins. 0:08:30.880,0:08:32.390 Because they don't[br]make their own. 0:08:32.390,0:08:35.860 That essentially cause the cell[br]to either kill itself or 0:08:35.860,0:08:37.140 its membrane to dissolve. 0:08:37.140,0:08:39.260 So the membrane dissolves. 0:08:39.260,0:08:41.480 And essentially the[br]cell lyses. 0:08:41.480,0:08:42.409 Let me write that down. 0:08:42.409,0:08:43.840 The cell lyses. 0:08:43.840,0:08:46.110 And lyses just means that[br]the cell's membrane just 0:08:46.110,0:08:46.900 disappears. 0:08:46.900,0:08:50.480 And then all of these guys can[br]emerge for themselves. 0:08:50.480,0:08:53.470 Now I talked about before that[br]have some of these guys, that 0:08:53.470,0:08:54.750 they have their own membrane. 0:08:54.750,0:08:56.710 So how did they get[br]there, these 0:08:56.710,0:08:58.400 kind of bilipid membranes? 0:08:58.400,0:09:00.900 Well some of them, what they[br]do is, once they replicate 0:09:00.900,0:09:07.380 inside of a cell, they exit[br]maybe not even killing-- they 0:09:07.380,0:09:08.650 don't have to lyse. 0:09:08.650,0:09:11.620 Everything I talk about, these[br]are specific ways that a virus 0:09:11.620,0:09:12.150 might work. 0:09:12.150,0:09:15.630 But viruses really kind of[br]explore-- well different types 0:09:15.630,0:09:17.620 of viruses do almost every[br]different combination you 0:09:17.620,0:09:22.610 could imagine of replicating[br]and coding for proteins and 0:09:22.610,0:09:23.400 escaping from cells. 0:09:23.400,0:09:24.720 Some of them just bud. 0:09:24.720,0:09:26.560 And when they bud, they[br]essentially, you can kind of 0:09:26.560,0:09:28.070 imagine that they push[br]against the cell 0:09:28.070,0:09:29.670 wall, or the membrane. 0:09:29.670,0:09:30.740 I shouldn't say cell wall. 0:09:30.740,0:09:32.630 The cell's outer membrane. 0:09:32.630,0:09:36.130 And then when they push against[br]it, they take some of 0:09:36.130,0:09:38.070 the membrane with them. 0:09:38.070,0:09:41.260 Until eventually the cell[br]will-- when this goes up 0:09:41.260,0:09:43.810 enough, this'll pop together[br]and it'll take some of the 0:09:43.810,0:09:44.565 membrane with it. 0:09:44.565,0:09:47.280 And you could imagine why that[br]would be useful thing 0:09:47.280,0:09:49.030 to have with you. 0:09:49.030,0:09:51.260 Because now that you have this[br]membrane, you kind of look 0:09:51.260,0:09:52.520 like this cell. 0:09:52.520,0:09:55.300 So when you want to go infect[br]another cell like this, you're 0:09:55.300,0:09:58.530 not going to necessarily look[br]like a foreign particle. 0:09:58.530,0:10:02.780 So it's a very useful way to[br]look like something that 0:10:02.780,0:10:03.470 you're not. 0:10:03.470,0:10:06.940 And if you don't think that this[br]is creepy-crawly enough, 0:10:06.940,0:10:10.780 that you're hijacking the DNA[br]of an organism, viruses can 0:10:10.780,0:10:14.740 actually change the[br]DNA an organism. 0:10:14.740,0:10:18.830 And actually one of the most[br]common examples is HIV virus. 0:10:18.830,0:10:21.480 Let me write that down. 0:10:21.480,0:10:27.480 HIV, which is a type of[br]retrovirus, which is 0:10:27.480,0:10:28.280 fascinating. 0:10:28.280,0:10:31.930 Because what they do is, so[br]they have RNA in them. 0:10:35.810,0:10:38.030 And when they enter into a cell,[br]let's say that they got 0:10:38.030,0:10:39.430 into the cell. 0:10:39.430,0:10:42.950 So it's inside of the[br]cell like this. 0:10:42.950,0:10:46.570 They actually bring along[br]with them a protein. 0:10:46.570,0:10:49.600 And every time you say, where[br]do they get this protein? 0:10:49.600,0:10:51.390 All of this stuff came from[br]a different cell. 0:10:51.390,0:10:54.490 They use some other cell's amino[br]acids and ribosomes and 0:10:54.490,0:10:56.800 nucleic acids and everything[br]to build themselves. 0:10:56.800,0:10:58.780 So any proteins that they[br]have in them came 0:10:58.780,0:11:00.080 from another cell. 0:11:00.080,0:11:04.610 But they bring with them, this[br]protein reverse transcriptase. 0:11:04.610,0:11:07.850 And the reverse transcriptase[br]takes their RNA and 0:11:07.850,0:11:11.490 codes it into DNA. 0:11:11.490,0:11:14.790 So its RNA to DNA. 0:11:14.790,0:11:16.810 Which when it was first[br]discovered was, kind of, 0:11:16.810,0:11:19.950 people always thought that you[br]always went from DNA to RNA, 0:11:19.950,0:11:22.110 but this kind of broke[br]that paradigm. 0:11:22.110,0:11:23.850 But it codes from RNA to DNA. 0:11:23.850,0:11:29.020 And if that's not bad enough,[br]it'll incorporate that DNA 0:11:29.020,0:11:31.350 into the DNA of the host cell. 0:11:31.350,0:11:34.500 So that DNA will incorporate[br]itself into the 0:11:34.500,0:11:35.200 DNA of the host cell. 0:11:35.200,0:11:37.690 Let's say the yellow is the[br]DNA of the host cell. 0:11:37.690,0:11:41.000 And this is its nucleus. 0:11:41.000,0:11:44.070 So it actually messes with[br]the genetic makeup 0:11:44.070,0:11:46.030 of what it's infecting. 0:11:46.030,0:11:51.570 And when I made the videos on[br]bacteria I said, hey for every 0:11:51.570,0:11:53.790 one human cell we have twenty[br]bacteria cells. 0:11:53.790,0:11:56.420 And they live with us and[br]they're useful and they're 0:11:56.420,0:12:00.100 part of us and they're 10% of[br]our dry mass and all of that. 0:12:00.100,0:12:02.170 But bacteria are kind of[br]along for the ride. 0:12:02.170,0:12:03.860 They don't change who we are. 0:12:03.860,0:12:07.010 But these retroviruses, they're[br]actually changing our 0:12:07.010,0:12:07.940 genetic makeup. 0:12:07.940,0:12:10.650 I mean, my genes, I take[br]very personally. 0:12:10.650,0:12:12.380 They define who I am. 0:12:12.380,0:12:14.630 But these guys will[br]actually go in and 0:12:14.630,0:12:16.240 change my genetic makeup. 0:12:16.240,0:12:19.300 And then once they're part of[br]the DNA, then just the natural 0:12:19.300,0:12:25.330 DNA to RNA to protein[br]process will code 0:12:25.330,0:12:27.180 their actual proteins. 0:12:27.180,0:12:30.160 Or their-- what they need to--[br]so sometimes they'll lay 0:12:30.160,0:12:31.420 dormant and do nothing. 0:12:31.420,0:12:33.730 And sometimes-- let's say[br]sometimes in some type of 0:12:33.730,0:12:35.790 environmental trigger,[br]they'll start coding 0:12:35.790,0:12:37.110 for themselves again. 0:12:37.110,0:12:38.620 And they'll start[br]producing more. 0:12:38.620,0:12:41.980 But they're producing it[br]directly from the organism's 0:12:41.980,0:12:43.110 cell's DNA. 0:12:43.110,0:12:45.120 They become part of[br]the organism. 0:12:45.120,0:12:49.280 I mean I can't imagine a more[br]intimate way to become part of 0:12:49.280,0:12:51.530 an organism than to become[br]part of its DNA. 0:12:51.530,0:12:52.870 I can't imagine any[br]other way to 0:12:52.870,0:12:55.680 actually define an organism. 0:12:55.680,0:13:00.910 And if this by itself is not[br]eerie enough, and just so you 0:13:00.910,0:13:06.770 know, this notion right here,[br]when a virus becomes part of 0:13:06.770,0:13:09.430 an organism's DNA, this[br]is called a provirus. 0:13:13.180,0:13:16.890 But if this isn't eerie enough,[br]they estimate-- so if 0:13:16.890,0:13:23.500 this infects a cell in my nose[br]or in my arm, as this cell 0:13:23.500,0:13:27.250 experiences mitosis, all of[br]its offspring-- but its 0:13:27.250,0:13:29.030 offspring are genetically[br]identical-- are going to have 0:13:29.030,0:13:30.600 this viral DNA. 0:13:30.600,0:13:32.060 And that might be fine,[br]but at least my 0:13:32.060,0:13:33.120 children won't get it. 0:13:33.120,0:13:35.980 You know, at least it won't[br]become part of my species. 0:13:35.980,0:13:38.710 But it doesn't have to just[br]infect somatic cells, it could 0:13:38.710,0:13:41.170 infect a germ cell. 0:13:41.170,0:13:44.510 So it could go into[br]a germ cell. 0:13:44.510,0:13:46.850 And the germ cells, we've[br]learned already, these are the 0:13:46.850,0:13:49.380 ones that produce gametes. 0:13:49.380,0:13:52.930 For men, that's sperm and[br]for women it's eggs. 0:13:52.930,0:13:55.180 But you could imagine, once[br]you've infected a germ cell, 0:13:55.180,0:13:59.010 once you become part of a germ[br]cell's DNA, then I'm passing 0:13:59.010,0:14:02.600 on that viral DNA to my[br]son or my daughter. 0:14:02.600,0:14:05.540 And they are going to pass[br]it on to their children. 0:14:05.540,0:14:10.260 And just that idea by itself[br]is, at least to my mind. 0:14:10.260,0:14:12.130 vaguely creepy. 0:14:12.130,0:14:16.050 And people estimate that 5-8%--[br]and this kind of really 0:14:16.050,0:14:19.480 blurs, it makes you think about[br]what we as humans really 0:14:19.480,0:14:26.800 are-- but the estimate is 5-8%[br]of the human genome-- so when 0:14:26.800,0:14:29.500 I talked about bacteria I just[br]talked about things that were 0:14:29.500,0:14:30.850 along for the ride. 0:14:30.850,0:14:33.240 But the current estimate, and[br]I looked up this a lot. 0:14:33.240,0:14:35.210 I found 8% someplace,[br]5% someplace. 0:14:35.210,0:14:35.990 It's all a guess. 0:14:35.990,0:14:37.650 I mean people are doing it based[br]on just looking at the 0:14:37.650,0:14:40.690 DNA and how similar it is to[br]DNA in other organisms. But 0:14:40.690,0:14:47.390 the estimate is 5-8% of the[br]human genome is from viruses, 0:14:47.390,0:14:51.760 is from ancient retroviruses[br]that incorporated themselves 0:14:51.760,0:14:53.530 into the human germ line. 0:14:53.530,0:14:55.725 So into the human DNA. 0:14:55.725,0:14:57.860 So these are called endogenous[br]retroviruses. 0:15:04.800,0:15:07.150 Which is mind blowing to me,[br]because it's not just saying 0:15:07.150,0:15:09.290 these things are along for the[br]ride or that they might help 0:15:09.290,0:15:10.070 us or hurt us. 0:15:10.070,0:15:14.000 It's saying that we are--[br]5-8% of our DNA 0:15:14.000,0:15:16.390 actually comes from viruses. 0:15:16.390,0:15:17.850 And this is another thing[br]that speaks to 0:15:17.850,0:15:19.720 just genetic variation. 0:15:19.720,0:15:24.210 Because viruses do something--[br]I mean this is called 0:15:24.210,0:15:27.760 horizontal transfer of DNA. 0:15:27.760,0:15:30.480 And you could imagine, as a[br]virus goes from one species to 0:15:30.480,0:15:37.220 the next, as it goes from[br]Species A to B, if it mutates 0:15:37.220,0:15:41.310 to be able to infiltrate these[br]cells, it might take some-- 0:15:41.310,0:15:43.810 it'll take the DNA that[br]it already has, that 0:15:43.810,0:15:45.490 makes it, it with it. 0:15:45.490,0:15:48.180 But sometimes, when it starts[br]coding for some of these other 0:15:48.180,0:15:52.830 guys, so let's say that this[br]is a provirus right here. 0:15:52.830,0:15:55.860 Where the blue part is[br]the original virus. 0:15:55.860,0:16:00.960 The yellow is the organism's[br]historic DNA. 0:16:00.960,0:16:04.230 Sometimes when it codes, it[br]takes up little sections of 0:16:04.230,0:16:07.200 the other organism's DNA. 0:16:07.200,0:16:11.810 So maybe most of it was the[br]viral DNA, but it might have, 0:16:11.810,0:16:14.070 when it transcribed and[br]translated itself, it might 0:16:14.070,0:16:16.710 have taken a little bit-- or at[br]least when it translated or 0:16:16.710,0:16:18.460 replicated itself-- it might[br]take a little bit of the 0:16:18.460,0:16:20.540 organism's previous DNA. 0:16:20.540,0:16:23.690 So it's actually cutting parts[br]of DNA from one organism and 0:16:23.690,0:16:24.950 bringing it to another[br]organism. 0:16:24.950,0:16:27.490 Taking it from one member of a[br]species to another member of 0:16:27.490,0:16:27.810 the species. 0:16:27.810,0:16:29.750 But it can definitely[br]go cross-species. 0:16:29.750,0:16:32.860 So you have this idea all of[br]a sudden that DNA can jump 0:16:32.860,0:16:34.090 between species. 0:16:34.090,0:16:36.410 It really kind of-- I don't[br]know, for me it makes me 0:16:36.410,0:16:39.930 appreciate how interconnected--[br]as a species, 0:16:39.930,0:16:41.950 we kind of imagine that we're[br]by ourselves and can only 0:16:41.950,0:16:45.110 reproduce with each other and[br]have genetic variation within 0:16:45.110,0:16:45.860 a population. 0:16:45.860,0:16:50.190 But viruses introduce this[br]notion of horizontal transfer 0:16:50.190,0:16:53.090 via transduction. 0:16:53.090,0:16:57.640 Horizontal transduction is just[br]the idea of, look when I 0:16:57.640,0:17:00.660 replicate this virus, I might[br]take a little bit of the 0:17:00.660,0:17:04.349 organism that I'm freeloading[br]off of, I might take a little 0:17:04.349,0:17:06.010 bit of their DNA with me. 0:17:06.010,0:17:09.160 And infect that DNA into[br]the next organism. 0:17:09.160,0:17:11.329 So you actually have this[br]DNA, this jumping, 0:17:11.329,0:17:13.119 from organism to organism. 0:17:13.119,0:17:17.300 So it kind of unifies[br]all DNA-based life. 0:17:17.300,0:17:20.609 Which is all the life that[br]we know on the planet. 0:17:20.609,0:17:24.900 And if all of this isn't creepy[br]enough-- and actually 0:17:24.900,0:17:28.540 maybe I'll save the creepiest[br]part for the end. 0:17:28.540,0:17:30.800 But there's a whole-- we could[br]talk all about the different 0:17:30.800,0:17:31.670 classes of viruses. 0:17:31.670,0:17:33.810 But just so you're familiar with[br]some of the terminology, 0:17:33.810,0:17:37.895 when a virus attacks bacteria,[br]which they often do. 0:17:37.895,0:17:41.150 And we study these the most[br]because this might be a good 0:17:41.150,0:17:42.630 alternative to antibiotics. 0:17:42.630,0:17:45.430 Because viruses that attack[br]bacteria might-- sometimes the 0:17:45.430,0:17:47.820 bacteria is far worse for the[br]virus-- but these are called 0:17:47.820,0:17:49.070 bacteriaphages. 0:17:52.610,0:17:55.320 And I've already talked to you[br]about how they have their DNA. 0:17:55.320,0:17:57.890 But since bacteria have hard[br]walls, they will just inject 0:17:57.890,0:18:00.940 the DNA inside of[br]the bacteria. 0:18:00.940,0:18:06.630 And when you talk about DNA,[br]this idea of a provirus. 0:18:06.630,0:18:09.170 So when a virus lyses it[br]like this, this is 0:18:09.170,0:18:11.090 called the lytic cycle. 0:18:11.090,0:18:13.760 This is just some terminology[br]that's good to know if you're 0:18:13.760,0:18:16.250 going to take a biology[br]exam about this stuff. 0:18:16.250,0:18:18.600 And when the virus incorporates[br]it into the DNA 0:18:18.600,0:18:22.350 and lays dormant, incorporates[br]into the DNA of the host 0:18:22.350,0:18:25.420 organism and lays dormant for[br]awhile, this is called the 0:18:25.420,0:18:28.030 lysogenic cycle. 0:18:28.030,0:18:32.030 And normally, a provirus is[br]essentially experiencing a 0:18:32.030,0:18:35.910 lysogenic cycle in eurkaryotes,[br]in organisms that 0:18:35.910,0:18:38.250 have a nuclear membrane. 0:18:38.250,0:18:40.890 Normally when people talk about[br]the lysogenic cycle, 0:18:40.890,0:18:44.750 they're talking about viral DNA[br]laying dormant in the DNA 0:18:44.750,0:18:45.600 of bacteria. 0:18:45.600,0:18:48.600 Or bacteriophage DNA[br]laying dormant 0:18:48.600,0:18:51.050 in the DNA of bacteria. 0:18:51.050,0:18:53.380 But just to kind of give you[br]an idea of what this, quote 0:18:53.380,0:18:59.480 unquote, looks like,[br]right here. 0:18:59.480,0:19:01.550 I got these two pictures[br]from Wikipedia. 0:19:01.550,0:19:02.800 One is from the CDC. 0:19:11.360,0:19:14.200 These little green dots you see[br]right here all over the 0:19:14.200,0:19:17.540 surface, this big thing you[br]see here, this is a white 0:19:17.540,0:19:20.330 blood cell. 0:19:20.330,0:19:21.760 Part of the human[br]immune system. 0:19:21.760,0:19:23.050 This is a white blood cell. 0:19:27.540,0:19:31.060 And what you see emerging from[br]the surface, essentially 0:19:31.060,0:19:34.510 budding from the surface of this[br]white blood cell-- and 0:19:34.510,0:19:36.300 this gives you a sense[br]of scale too-- 0:19:36.300,0:19:39.700 these are HIV-1 viruses. 0:19:39.700,0:19:46.970 And so you're familiar with the[br]terminology, the HIV is a 0:19:46.970,0:19:51.810 virus that infects white[br]blood cells. 0:19:51.810,0:19:54.890 AIDS is the syndrome you get[br]once your immune system is 0:19:54.890,0:19:55.900 weakened to the point. 0:19:55.900,0:19:58.860 And then many people suffer[br]infections that people with a 0:19:58.860,0:20:01.450 strong immune system normally[br]won't suffer from. 0:20:01.450,0:20:03.050 But this is creepy. 0:20:03.050,0:20:06.360 These things went inside this[br]huge cell, they used the 0:20:06.360,0:20:11.555 cell's own mechanism to[br]reproduce its own DNA or its 0:20:11.555,0:20:14.300 own RNA and these[br]protein capsids. 0:20:14.300,0:20:16.270 And then they bud from the cell[br]and take a little bit of 0:20:16.270,0:20:17.490 the membrane with it. 0:20:17.490,0:20:20.990 And they can even leave some[br]of their DNA behind in this 0:20:20.990,0:20:22.340 cell's own DNA. 0:20:22.340,0:20:25.280 So they really change what[br]the cell is all about. 0:20:25.280,0:20:26.890 This is another creepy[br]picture. 0:20:26.890,0:20:28.140 These are bacteriaphages. 0:20:34.500,0:20:36.110 And these show you what[br]I said before. 0:20:36.110,0:20:38.450 This is a bacteria right here. 0:20:38.450,0:20:41.360 This is its cell wall. 0:20:41.360,0:20:42.100 And it's hard. 0:20:42.100,0:20:45.020 So it's hard to just[br]emerge into it. 0:20:45.020,0:20:47.040 Or you can't just merge,[br]fuse membranes with it. 0:20:47.040,0:20:52.290 So they hang out on the outside[br]of this bacteria. 0:20:52.290,0:20:55.410 And they are essentially[br]injecting their genetic 0:20:55.410,0:20:58.280 material into the[br]bacteria itself. 0:20:58.280,0:20:59.890 And you could imagine,[br]just looking at the 0:20:59.890,0:21:01.000 size of these things. 0:21:01.000,0:21:02.090 I mean, this is a cell. 0:21:02.090,0:21:04.350 And it looks like a whole[br]planet or something. 0:21:04.350,0:21:05.650 Or this is a bacteria and these 0:21:05.650,0:21:06.620 things are so much smaller. 0:21:06.620,0:21:08.170 Roughly 1/100 of a bacteria. 0:21:08.170,0:21:10.570 And these are much less than[br]1/100 of this cell we're 0:21:10.570,0:21:11.110 talking about. 0:21:11.110,0:21:15.510 And they're extremely[br]hard to filter for. 0:21:15.510,0:21:16.520 To kind of keep out. 0:21:16.520,0:21:20.780 Because they are such,[br]such small particles. 0:21:20.780,0:21:23.290 If you think that these are[br]exotic things that exist for 0:21:23.290,0:21:31.360 things like HIV or Ebola , which[br]they do cause, or SARS, 0:21:31.360,0:21:32.340 you're right. 0:21:32.340,0:21:33.730 But they're also[br]common things. 0:21:33.730,0:21:35.490 I mean, I said at the beginning[br]of this video that I 0:21:35.490,0:21:36.300 have a cold. 0:21:36.300,0:21:40.040 And I have a cold because some[br]viruses have infected the 0:21:40.040,0:21:42.610 tissue in my nasal passage. 0:21:42.610,0:21:46.190 And they're causing me to have[br]a runny nose and whatnot. 0:21:46.190,0:21:48.540 And viruses also cause[br]the chicken pox. 0:21:48.540,0:21:50.550 They cause the herpes[br]simplex virus. 0:21:50.550,0:21:51.540 Causes cold sores. 0:21:51.540,0:21:53.430 So they're with us all around. 0:21:53.430,0:21:56.000 I can almost guarantee[br]you have some virus 0:21:56.000,0:21:57.740 with you as you speak. 0:21:57.740,0:21:58.630 They're all around you. 0:21:58.630,0:22:04.320 But it's a very 0:22:04.320,0:22:06.480 philosophically puzzling question. 0:22:06.480,0:22:09.090 Because I started with, at the[br]beginning, are these life? 0:22:09.090,0:22:11.495 And at first when I just showed[br]it to you, look they 0:22:11.495,0:22:13.740 are just this protein[br]with some nucleic 0:22:13.740,0:22:15.280 acid molecule in it. 0:22:15.280,0:22:16.340 And it's not doing anything. 0:22:16.340,0:22:17.780 And that doesn't look[br]like life to me. 0:22:17.780,0:22:18.610 It's not moving around. 0:22:18.610,0:22:19.660 It doesn't have a metabolism. 0:22:19.660,0:22:20.390 It's not eating. 0:22:20.390,0:22:21.560 It's not reproducing. 0:22:21.560,0:22:23.120 But then all of a sudden, when[br]you think about what it's 0:22:23.120,0:22:27.130 doing to cells and how it uses[br]cells to kind of reproduce. 0:22:27.130,0:22:29.700 It kind of like-- in business[br]terms it's asset light. 0:22:29.700,0:22:31.920 It doesn't need all of the[br]machinery because it can use 0:22:31.920,0:22:35.850 other people's machinery[br]to replicate itself. 0:22:35.850,0:22:38.080 You almost kind of want[br]to view it as a 0:22:38.080,0:22:39.520 smarter form of life. 0:22:39.520,0:22:42.480 Because it doesn't go through[br]all of the trouble of what 0:22:42.480,0:22:44.110 every other form of life has. 0:22:44.110,0:22:47.570 It makes you question what life[br]is, or even what we are. 0:22:47.570,0:22:51.510 Are we these things that contain[br]DNA or are we just 0:22:51.510,0:22:54.170 transport mechanisms[br]for the DNA? 0:22:54.170,0:22:56.260 And these are kind of the[br]more important things. 0:22:56.260,0:22:59.710 And these viral infections are[br]just battles between different 0:22:59.710,0:23:02.340 forms of DNA and RNA[br]and whatnot. 0:23:02.340,0:23:04.330 Anyway I don't want to get[br]too philosophical on you. 0:23:04.330,0:23:08.840 But hopefully this gives you a[br]good idea of what viruses are 0:23:08.840,0:23:12.940 and why they really are, in my[br]mind, the most fascinating 0:23:12.940,0:23:15.870 pseudo organism in[br]all of biology.