1 00:00:00,000 --> 00:00:00,470 2 00:00:00,470 --> 00:00:03,210 Considering that I have a cold right now, I can't imagine a 3 00:00:03,210 --> 00:00:08,109 more appropriate topic to make a video on than a virus. 4 00:00:08,109 --> 00:00:09,930 And I didn't want to make it that thick. 5 00:00:09,930 --> 00:00:11,380 A virus, or viruses. 6 00:00:11,380 --> 00:00:14,760 7 00:00:14,760 --> 00:00:19,080 And in my opinion, viruses are, on some level, the most 8 00:00:19,080 --> 00:00:21,450 fascinating thing in all of biology. 9 00:00:21,450 --> 00:00:25,560 Because they really blur the boundary between what is an 10 00:00:25,560 --> 00:00:27,440 inanimate object and what is life? 11 00:00:27,440 --> 00:00:30,080 12 00:00:30,080 --> 00:00:33,410 I mean if we look at ourselves, or life as one of 13 00:00:33,410 --> 00:00:35,210 those things that you know it when you see it. 14 00:00:35,210 --> 00:00:39,300 If you see something that, it's born, it grows, it's 15 00:00:39,300 --> 00:00:40,460 constantly changing. 16 00:00:40,460 --> 00:00:41,510 Maybe it moves around. 17 00:00:41,510 --> 00:00:42,260 Maybe it doesn't. 18 00:00:42,260 --> 00:00:44,400 But it's metabolizing things around itself. 19 00:00:44,400 --> 00:00:46,310 It reproduces and then it dies. 20 00:00:46,310 --> 00:00:48,300 You say, hey, that's probably life. 21 00:00:48,300 --> 00:00:50,960 And in this, we throw most things that we see-- or we 22 00:00:50,960 --> 00:00:52,815 throw in, us. 23 00:00:52,815 --> 00:00:55,360 We throw in bacteria. 24 00:00:55,360 --> 00:00:57,120 We throw in plants. 25 00:00:57,120 --> 00:01:00,830 I mean, I could-- I'm kind of butchering the taxonomy system 26 00:01:00,830 --> 00:01:03,275 here, but we tend to know life when we see it. 27 00:01:03,275 --> 00:01:07,480 But all viruses are, they're just a bunch of genetic 28 00:01:07,480 --> 00:01:09,740 information inside of a protein. 29 00:01:09,740 --> 00:01:11,230 Inside of a protein capsule. 30 00:01:11,230 --> 00:01:13,490 So let me draw. 31 00:01:13,490 --> 00:01:16,340 And the genetic information can come in any form. 32 00:01:16,340 --> 00:01:22,240 So it can be an RNA, it could be DNA, it could be 33 00:01:22,240 --> 00:01:24,670 single-stranded RNA, double-stranded RNA. 34 00:01:24,670 --> 00:01:27,260 Sometimes for single stranded they'll write these two little 35 00:01:27,260 --> 00:01:29,250 S's in front of it. 36 00:01:29,250 --> 00:01:30,950 Let's say they are talking about double stranded DNA, 37 00:01:30,950 --> 00:01:32,910 they'll put a ds in front of it. 38 00:01:32,910 --> 00:01:35,330 But the general idea-- and viruses can come in all of 39 00:01:35,330 --> 00:01:38,110 these forms-- is that they have some genetic information, 40 00:01:38,110 --> 00:01:40,530 some chain of nucleic acids. 41 00:01:40,530 --> 00:01:43,730 Either as single or double stranded RNA or single or 42 00:01:43,730 --> 00:01:44,560 double stranded DNA. 43 00:01:44,560 --> 00:01:47,970 And it's just contained inside some type of protein 44 00:01:47,970 --> 00:01:49,880 structure, which is called the capsid. 45 00:01:49,880 --> 00:01:53,240 And kind of the classic drawing is kind of an 46 00:01:53,240 --> 00:01:56,650 icosahedron type looking thing. 47 00:01:56,650 --> 00:01:58,200 Let me see if I can do justice to it. 48 00:01:58,200 --> 00:02:00,610 It looks something like this. 49 00:02:00,610 --> 00:02:02,800 And not all viruses have to look exactly like this. 50 00:02:02,800 --> 00:02:05,160 There's thousands of types of viruses. 51 00:02:05,160 --> 00:02:06,850 And we're really just scratching the surface and 52 00:02:06,850 --> 00:02:09,630 understanding even what viruses are out there and all 53 00:02:09,630 --> 00:02:14,800 of the different ways that they can essentially replicate 54 00:02:14,800 --> 00:02:15,220 themselves. 55 00:02:15,220 --> 00:02:16,620 We'll talk more about that in the future. 56 00:02:16,620 --> 00:02:19,110 And I would suspect that pretty much any possible way 57 00:02:19,110 --> 00:02:21,530 of replication probably does somehow exist 58 00:02:21,530 --> 00:02:22,750 in the virus world. 59 00:02:22,750 --> 00:02:25,260 But they really are just these proteins, these protein 60 00:02:25,260 --> 00:02:27,450 capsids, are just made up of a bunch of little 61 00:02:27,450 --> 00:02:29,070 proteins put together. 62 00:02:29,070 --> 00:02:31,250 And inside they have some genetic material, which might 63 00:02:31,250 --> 00:02:33,700 be DNA or it might be RNA. 64 00:02:33,700 --> 00:02:35,870 So let me draw their genetic material. 65 00:02:35,870 --> 00:02:38,420 The protein is not necessarily transparent, but if it was, 66 00:02:38,420 --> 00:02:42,960 you would see some genetic material inside of there. 67 00:02:42,960 --> 00:02:48,440 So the question is, is this thing life? 68 00:02:48,440 --> 00:02:49,580 It seems pretty inanimate. 69 00:02:49,580 --> 00:02:50,540 It doesn't grow. 70 00:02:50,540 --> 00:02:51,510 It doesn't change. 71 00:02:51,510 --> 00:02:53,200 It doesn't metabolize things. 72 00:02:53,200 --> 00:02:55,200 This thing, left to its own devices, is just 73 00:02:55,200 --> 00:02:55,850 going to sit there. 74 00:02:55,850 --> 00:02:59,600 It's just going to sit there the way a book on a table just 75 00:02:59,600 --> 00:03:00,690 sits there. 76 00:03:00,690 --> 00:03:02,280 It won't change anything. 77 00:03:02,280 --> 00:03:06,560 But what happens is, the debate arises. 78 00:03:06,560 --> 00:03:08,470 I mean you might say, hey Sal, when you define it that way, 79 00:03:08,470 --> 00:03:10,690 just looks like a bunch of molecules put together. 80 00:03:10,690 --> 00:03:11,740 That isn't life. 81 00:03:11,740 --> 00:03:14,350 But it starts to seem like life all of a sudden when it 82 00:03:14,350 --> 00:03:17,100 comes in contact with the things that we normally 83 00:03:17,100 --> 00:03:18,220 consider life. 84 00:03:18,220 --> 00:03:22,480 So what viruses do, the classic example is, a virus 85 00:03:22,480 --> 00:03:24,680 will attach itself to a cell. 86 00:03:24,680 --> 00:03:28,590 So let me draw this thing a little bit smaller. 87 00:03:28,590 --> 00:03:30,260 So let's say that this is my virus. 88 00:03:30,260 --> 00:03:32,562 I'll draw it as a little hexagon. 89 00:03:32,562 --> 00:03:34,980 And what it does is, it'll attach itself to a cell. 90 00:03:34,980 --> 00:03:35,795 And it could be any type of cell. 91 00:03:35,795 --> 00:03:39,155 It could be a bacteria cell, it could be a plant cell, it 92 00:03:39,155 --> 00:03:41,190 could be a human cell. 93 00:03:41,190 --> 00:03:43,820 Let me draw the cell here. 94 00:03:43,820 --> 00:03:48,540 Cells are usually far larger than the virus. 95 00:03:48,540 --> 00:03:51,610 In the case of cells that have soft membranes, the virus 96 00:03:51,610 --> 00:03:53,850 figures out some way to enter it. 97 00:03:53,850 --> 00:03:58,780 Sometimes it can essentially fuse-- I don't want to 98 00:03:58,780 --> 00:04:01,390 complicate the issue-- but sometimes viruses have their 99 00:04:01,390 --> 00:04:02,480 own little membranes. 100 00:04:02,480 --> 00:04:03,740 And we'll talk about in a second where 101 00:04:03,740 --> 00:04:04,760 it gets their membranes. 102 00:04:04,760 --> 00:04:08,270 So a virus might have its own membrane like that. 103 00:04:08,270 --> 00:04:10,520 That's around its capsid. 104 00:04:10,520 --> 00:04:13,470 And then these membranes will fuse. 105 00:04:13,470 --> 00:04:16,785 And then the virus will be able to enter into the cell. 106 00:04:16,785 --> 00:04:18,000 Now, that's one method. 107 00:04:18,000 --> 00:04:19,670 And another method, and they're seldom 108 00:04:19,670 --> 00:04:20,589 all the same way. 109 00:04:20,589 --> 00:04:24,020 But let's say another method would be, the virus 110 00:04:24,020 --> 00:04:26,910 convinces-- just based on some protein receptors on it, or 111 00:04:26,910 --> 00:04:29,810 protein receptors on the cells-- and obviously this has 112 00:04:29,810 --> 00:04:31,650 to be kind of a Trojan horse type of thing. 113 00:04:31,650 --> 00:04:33,600 The cell doesn't want viruses. 114 00:04:33,600 --> 00:04:36,390 So the virus has to somehow convince the cell that it's a 115 00:04:36,390 --> 00:04:38,050 non-foreign particle. 116 00:04:38,050 --> 00:04:41,770 We could do hundreds of videos on how viruses work and it's a 117 00:04:41,770 --> 00:04:43,430 continuing field of research. 118 00:04:43,430 --> 00:04:47,580 But sometimes you might have a virus that just gets consumed 119 00:04:47,580 --> 00:04:48,120 by the cell. 120 00:04:48,120 --> 00:04:49,930 Maybe the cell just thinks it's something that it needs 121 00:04:49,930 --> 00:04:50,960 to consume. 122 00:04:50,960 --> 00:04:53,130 So the cell wraps around it like this. 123 00:04:53,130 --> 00:04:56,780 124 00:04:56,780 --> 00:04:58,930 And these sides will eventually merge. 125 00:04:58,930 --> 00:05:01,670 And then the cell and the virus will go into it. 126 00:05:01,670 --> 00:05:03,160 This is called endocytosis. 127 00:05:03,160 --> 00:05:04,020 I'll just talk about that. 128 00:05:04,020 --> 00:05:06,640 It just brings it into its cytoplasm. 129 00:05:06,640 --> 00:05:11,020 It doesn't happen just to viruses. 130 00:05:11,020 --> 00:05:12,890 But this is one mechanism that can enter. 131 00:05:12,890 --> 00:05:17,320 And then in cases where the cell in question-- for example 132 00:05:17,320 --> 00:05:20,280 in the situation with bacteria-- if the cell has a 133 00:05:20,280 --> 00:05:25,520 very hard shell-- let me do it in a good color. 134 00:05:25,520 --> 00:05:29,040 So let's say that this is a bacteria right here. 135 00:05:29,040 --> 00:05:30,510 And it has a hard shell. 136 00:05:30,510 --> 00:05:32,830 The viruses don't even enter the cell. 137 00:05:32,830 --> 00:05:36,440 They just hang out outside of the cell like this. 138 00:05:36,440 --> 00:05:37,740 Not drawing to scale. 139 00:05:37,740 --> 00:05:40,690 And they actually inject their genetic material. 140 00:05:40,690 --> 00:05:43,790 So there's obviously a huge-- there's a wide variety of ways 141 00:05:43,790 --> 00:05:45,680 of how the viruses get into cells. 142 00:05:45,680 --> 00:05:46,780 But that's beside the point. 143 00:05:46,780 --> 00:05:49,420 The interesting thing is that they do get into the cell. 144 00:05:49,420 --> 00:05:52,240 And once they do get into the cell, they release their 145 00:05:52,240 --> 00:05:54,570 genetic material into the cell. 146 00:05:54,570 --> 00:05:56,970 So their genetic material will float around. 147 00:05:56,970 --> 00:06:01,390 If their genetic material is already in the form of RNA-- 148 00:06:01,390 --> 00:06:05,700 and I could imagine almost every possibility of different 149 00:06:05,700 --> 00:06:08,160 ways for viruses to work probably do exist in nature. 150 00:06:08,160 --> 00:06:09,400 We just haven't found them. 151 00:06:09,400 --> 00:06:11,630 But the ones that we've already found really do kind 152 00:06:11,630 --> 00:06:13,880 of do it in every possible way. 153 00:06:13,880 --> 00:06:20,720 So if they have RNA, this RNA can immediately start being 154 00:06:20,720 --> 00:06:23,170 used to essentially-- let's say this is the 155 00:06:23,170 --> 00:06:25,540 nucleus of the cell. 156 00:06:25,540 --> 00:06:28,850 That's the nucleus of the cell and it normally has the DNA in 157 00:06:28,850 --> 00:06:29,480 it like that. 158 00:06:29,480 --> 00:06:30,720 Maybe I'll do the DNA in a different color. 159 00:06:30,720 --> 00:06:37,260 But DNA gets transcribed into RNA, normally. 160 00:06:37,260 --> 00:06:39,940 So normally, the cell, this a normal working cell, the RNA 161 00:06:39,940 --> 00:06:43,540 exits the nucleus, it goes to the ribosomes, and then you 162 00:06:43,540 --> 00:06:46,690 have the RNA in conjunction with the tRNA and it produces 163 00:06:46,690 --> 00:06:49,260 these proteins. 164 00:06:49,260 --> 00:06:51,030 The RNA codes for different proteins. 165 00:06:51,030 --> 00:06:53,670 And I talk about that in a different video. 166 00:06:53,670 --> 00:06:57,000 So these proteins get formed and eventually, they can form 167 00:06:57,000 --> 00:06:58,800 the different structures in a cell. 168 00:06:58,800 --> 00:07:03,190 But what a virus does is it hijacks this process here. 169 00:07:03,190 --> 00:07:04,490 Hijacks this mechanism. 170 00:07:04,490 --> 00:07:08,550 This RNA will essentially go and do what the cell's own RNA 171 00:07:08,550 --> 00:07:09,230 would have done. 172 00:07:09,230 --> 00:07:11,140 And it starts coding for its own proteins. 173 00:07:11,140 --> 00:07:12,250 Obviously it's not going to code for 174 00:07:12,250 --> 00:07:13,260 the same things there. 175 00:07:13,260 --> 00:07:15,790 And actually some of the first proteins it codes for often 176 00:07:15,790 --> 00:07:19,670 start killing the DNA and the RNA that might otherwise 177 00:07:19,670 --> 00:07:20,380 compete with it. 178 00:07:20,380 --> 00:07:22,390 So it codes its own proteins. 179 00:07:22,390 --> 00:07:26,860 And then those proteins start making more viral shells. 180 00:07:26,860 --> 00:07:31,520 So those proteins just start constructing more and more 181 00:07:31,520 --> 00:07:33,840 viral shells. 182 00:07:33,840 --> 00:07:36,000 At the same time, this RNA is replicating. 183 00:07:36,000 --> 00:07:39,730 It's using the cell's own mechanisms. Left to its own 184 00:07:39,730 --> 00:07:40,820 devices it would just sit there. 185 00:07:40,820 --> 00:07:43,800 But once it enters into a cell it can use all of the nice 186 00:07:43,800 --> 00:07:47,000 machinery that a cell has around to replicate itself. 187 00:07:47,000 --> 00:07:51,360 And it's kind of amazing, just the biochemistry of it. 188 00:07:51,360 --> 00:07:54,810 That these RNA molecules then find themselves 189 00:07:54,810 --> 00:07:57,470 back in these capsids. 190 00:07:57,470 --> 00:08:00,290 And then once there's enough of these and the cell has 191 00:08:00,290 --> 00:08:05,620 essentially all of its resources have been depleted, 192 00:08:05,620 --> 00:08:09,990 the viruses, these individual new viruses that have 193 00:08:09,990 --> 00:08:15,410 replicated themselves using all of the cell's mechanisms, 194 00:08:15,410 --> 00:08:17,370 will find some way to exit the cell. 195 00:08:17,370 --> 00:08:20,860 The most-- I don't want to say, typical, because we 196 00:08:20,860 --> 00:08:23,110 haven't even discovered all the different types of viruses 197 00:08:23,110 --> 00:08:26,750 there are-- but one that's, I guess, talked about the most, 198 00:08:26,750 --> 00:08:28,760 is when there's enough of these, they'll release 199 00:08:28,760 --> 00:08:30,880 proteins or they'll construct proteins. 200 00:08:30,880 --> 00:08:32,390 Because they don't make their own. 201 00:08:32,390 --> 00:08:35,860 That essentially cause the cell to either kill itself or 202 00:08:35,860 --> 00:08:37,140 its membrane to dissolve. 203 00:08:37,140 --> 00:08:39,260 So the membrane dissolves. 204 00:08:39,260 --> 00:08:41,480 And essentially the cell lyses. 205 00:08:41,480 --> 00:08:42,409 Let me write that down. 206 00:08:42,409 --> 00:08:43,840 The cell lyses. 207 00:08:43,840 --> 00:08:46,110 And lyses just means that the cell's membrane just 208 00:08:46,110 --> 00:08:46,900 disappears. 209 00:08:46,900 --> 00:08:50,480 And then all of these guys can emerge for themselves. 210 00:08:50,480 --> 00:08:53,470 Now I talked about before that have some of these guys, that 211 00:08:53,470 --> 00:08:54,750 they have their own membrane. 212 00:08:54,750 --> 00:08:56,710 So how did they get there, these 213 00:08:56,710 --> 00:08:58,400 kind of bilipid membranes? 214 00:08:58,400 --> 00:09:00,900 Well some of them, what they do is, once they replicate 215 00:09:00,900 --> 00:09:07,380 inside of a cell, they exit maybe not even killing-- they 216 00:09:07,380 --> 00:09:08,650 don't have to lyse. 217 00:09:08,650 --> 00:09:11,620 Everything I talk about, these are specific ways that a virus 218 00:09:11,620 --> 00:09:12,150 might work. 219 00:09:12,150 --> 00:09:15,630 But viruses really kind of explore-- well different types 220 00:09:15,630 --> 00:09:17,620 of viruses do almost every different combination you 221 00:09:17,620 --> 00:09:22,610 could imagine of replicating and coding for proteins and 222 00:09:22,610 --> 00:09:23,400 escaping from cells. 223 00:09:23,400 --> 00:09:24,720 Some of them just bud. 224 00:09:24,720 --> 00:09:26,560 And when they bud, they essentially, you can kind of 225 00:09:26,560 --> 00:09:28,070 imagine that they push against the cell 226 00:09:28,070 --> 00:09:29,670 wall, or the membrane. 227 00:09:29,670 --> 00:09:30,740 I shouldn't say cell wall. 228 00:09:30,740 --> 00:09:32,630 The cell's outer membrane. 229 00:09:32,630 --> 00:09:36,130 And then when they push against it, they take some of 230 00:09:36,130 --> 00:09:38,070 the membrane with them. 231 00:09:38,070 --> 00:09:41,260 Until eventually the cell will-- when this goes up 232 00:09:41,260 --> 00:09:43,810 enough, this'll pop together and it'll take some of the 233 00:09:43,810 --> 00:09:44,565 membrane with it. 234 00:09:44,565 --> 00:09:47,280 And you could imagine why that would be useful thing 235 00:09:47,280 --> 00:09:49,030 to have with you. 236 00:09:49,030 --> 00:09:51,260 Because now that you have this membrane, you kind of look 237 00:09:51,260 --> 00:09:52,520 like this cell. 238 00:09:52,520 --> 00:09:55,300 So when you want to go infect another cell like this, you're 239 00:09:55,300 --> 00:09:58,530 not going to necessarily look like a foreign particle. 240 00:09:58,530 --> 00:10:02,780 So it's a very useful way to look like something that 241 00:10:02,780 --> 00:10:03,470 you're not. 242 00:10:03,470 --> 00:10:06,940 And if you don't think that this is creepy-crawly enough, 243 00:10:06,940 --> 00:10:10,780 that you're hijacking the DNA of an organism, viruses can 244 00:10:10,780 --> 00:10:14,740 actually change the DNA an organism. 245 00:10:14,740 --> 00:10:18,830 And actually one of the most common examples is HIV virus. 246 00:10:18,830 --> 00:10:21,480 Let me write that down. 247 00:10:21,480 --> 00:10:27,480 HIV, which is a type of retrovirus, which is 248 00:10:27,480 --> 00:10:28,280 fascinating. 249 00:10:28,280 --> 00:10:31,930 Because what they do is, so they have RNA in them. 250 00:10:31,930 --> 00:10:35,810 251 00:10:35,810 --> 00:10:38,030 And when they enter into a cell, let's say that they got 252 00:10:38,030 --> 00:10:39,430 into the cell. 253 00:10:39,430 --> 00:10:42,950 So it's inside of the cell like this. 254 00:10:42,950 --> 00:10:46,570 They actually bring along with them a protein. 255 00:10:46,570 --> 00:10:49,600 And every time you say, where do they get this protein? 256 00:10:49,600 --> 00:10:51,390 All of this stuff came from a different cell. 257 00:10:51,390 --> 00:10:54,490 They use some other cell's amino acids and ribosomes and 258 00:10:54,490 --> 00:10:56,800 nucleic acids and everything to build themselves. 259 00:10:56,800 --> 00:10:58,780 So any proteins that they have in them came 260 00:10:58,780 --> 00:11:00,080 from another cell. 261 00:11:00,080 --> 00:11:04,610 But they bring with them, this protein reverse transcriptase. 262 00:11:04,610 --> 00:11:07,850 And the reverse transcriptase takes their RNA and 263 00:11:07,850 --> 00:11:11,490 codes it into DNA. 264 00:11:11,490 --> 00:11:14,790 So its RNA to DNA. 265 00:11:14,790 --> 00:11:16,810 Which when it was first discovered was, kind of, 266 00:11:16,810 --> 00:11:19,950 people always thought that you always went from DNA to RNA, 267 00:11:19,950 --> 00:11:22,110 but this kind of broke that paradigm. 268 00:11:22,110 --> 00:11:23,850 But it codes from RNA to DNA. 269 00:11:23,850 --> 00:11:29,020 And if that's not bad enough, it'll incorporate that DNA 270 00:11:29,020 --> 00:11:31,350 into the DNA of the host cell. 271 00:11:31,350 --> 00:11:34,500 So that DNA will incorporate itself into the 272 00:11:34,500 --> 00:11:35,200 DNA of the host cell. 273 00:11:35,200 --> 00:11:37,690 Let's say the yellow is the DNA of the host cell. 274 00:11:37,690 --> 00:11:41,000 And this is its nucleus. 275 00:11:41,000 --> 00:11:44,070 So it actually messes with the genetic makeup 276 00:11:44,070 --> 00:11:46,030 of what it's infecting. 277 00:11:46,030 --> 00:11:51,570 And when I made the videos on bacteria I said, hey for every 278 00:11:51,570 --> 00:11:53,790 one human cell we have twenty bacteria cells. 279 00:11:53,790 --> 00:11:56,420 And they live with us and they're useful and they're 280 00:11:56,420 --> 00:12:00,100 part of us and they're 10% of our dry mass and all of that. 281 00:12:00,100 --> 00:12:02,170 But bacteria are kind of along for the ride. 282 00:12:02,170 --> 00:12:03,860 They don't change who we are. 283 00:12:03,860 --> 00:12:07,010 But these retroviruses, they're actually changing our 284 00:12:07,010 --> 00:12:07,940 genetic makeup. 285 00:12:07,940 --> 00:12:10,650 I mean, my genes, I take very personally. 286 00:12:10,650 --> 00:12:12,380 They define who I am. 287 00:12:12,380 --> 00:12:14,630 But these guys will actually go in and 288 00:12:14,630 --> 00:12:16,240 change my genetic makeup. 289 00:12:16,240 --> 00:12:19,300 And then once they're part of the DNA, then just the natural 290 00:12:19,300 --> 00:12:25,330 DNA to RNA to protein process will code 291 00:12:25,330 --> 00:12:27,180 their actual proteins. 292 00:12:27,180 --> 00:12:30,160 Or their-- what they need to-- so sometimes they'll lay 293 00:12:30,160 --> 00:12:31,420 dormant and do nothing. 294 00:12:31,420 --> 00:12:33,730 And sometimes-- let's say sometimes in some type of 295 00:12:33,730 --> 00:12:35,790 environmental trigger, they'll start coding 296 00:12:35,790 --> 00:12:37,110 for themselves again. 297 00:12:37,110 --> 00:12:38,620 And they'll start producing more. 298 00:12:38,620 --> 00:12:41,980 But they're producing it directly from the organism's 299 00:12:41,980 --> 00:12:43,110 cell's DNA. 300 00:12:43,110 --> 00:12:45,120 They become part of the organism. 301 00:12:45,120 --> 00:12:49,280 I mean I can't imagine a more intimate way to become part of 302 00:12:49,280 --> 00:12:51,530 an organism than to become part of its DNA. 303 00:12:51,530 --> 00:12:52,870 I can't imagine any other way to 304 00:12:52,870 --> 00:12:55,680 actually define an organism. 305 00:12:55,680 --> 00:13:00,910 And if this by itself is not eerie enough, and just so you 306 00:13:00,910 --> 00:13:06,770 know, this notion right here, when a virus becomes part of 307 00:13:06,770 --> 00:13:09,430 an organism's DNA, this is called a provirus. 308 00:13:09,430 --> 00:13:13,180 309 00:13:13,180 --> 00:13:16,890 But if this isn't eerie enough, they estimate-- so if 310 00:13:16,890 --> 00:13:23,500 this infects a cell in my nose or in my arm, as this cell 311 00:13:23,500 --> 00:13:27,250 experiences mitosis, all of its offspring-- but its 312 00:13:27,250 --> 00:13:29,030 offspring are genetically identical-- are going to have 313 00:13:29,030 --> 00:13:30,600 this viral DNA. 314 00:13:30,600 --> 00:13:32,060 And that might be fine, but at least my 315 00:13:32,060 --> 00:13:33,120 children won't get it. 316 00:13:33,120 --> 00:13:35,980 You know, at least it won't become part of my species. 317 00:13:35,980 --> 00:13:38,710 But it doesn't have to just infect somatic cells, it could 318 00:13:38,710 --> 00:13:41,170 infect a germ cell. 319 00:13:41,170 --> 00:13:44,510 So it could go into a germ cell. 320 00:13:44,510 --> 00:13:46,850 And the germ cells, we've learned already, these are the 321 00:13:46,850 --> 00:13:49,380 ones that produce gametes. 322 00:13:49,380 --> 00:13:52,930 For men, that's sperm and for women it's eggs. 323 00:13:52,930 --> 00:13:55,180 But you could imagine, once you've infected a germ cell, 324 00:13:55,180 --> 00:13:59,010 once you become part of a germ cell's DNA, then I'm passing 325 00:13:59,010 --> 00:14:02,600 on that viral DNA to my son or my daughter. 326 00:14:02,600 --> 00:14:05,540 And they are going to pass it on to their children. 327 00:14:05,540 --> 00:14:10,260 And just that idea by itself is, at least to my mind. 328 00:14:10,260 --> 00:14:12,130 vaguely creepy. 329 00:14:12,130 --> 00:14:16,050 And people estimate that 5-8%-- and this kind of really 330 00:14:16,050 --> 00:14:19,480 blurs, it makes you think about what we as humans really 331 00:14:19,480 --> 00:14:26,800 are-- but the estimate is 5-8% of the human genome-- so when 332 00:14:26,800 --> 00:14:29,500 I talked about bacteria I just talked about things that were 333 00:14:29,500 --> 00:14:30,850 along for the ride. 334 00:14:30,850 --> 00:14:33,240 But the current estimate, and I looked up this a lot. 335 00:14:33,240 --> 00:14:35,210 I found 8% someplace, 5% someplace. 336 00:14:35,210 --> 00:14:35,990 It's all a guess. 337 00:14:35,990 --> 00:14:37,650 I mean people are doing it based on just looking at the 338 00:14:37,650 --> 00:14:40,690 DNA and how similar it is to DNA in other organisms. But 339 00:14:40,690 --> 00:14:47,390 the estimate is 5-8% of the human genome is from viruses, 340 00:14:47,390 --> 00:14:51,760 is from ancient retroviruses that incorporated themselves 341 00:14:51,760 --> 00:14:53,530 into the human germ line. 342 00:14:53,530 --> 00:14:55,725 So into the human DNA. 343 00:14:55,725 --> 00:14:57,860 So these are called endogenous retroviruses. 344 00:14:57,860 --> 00:15:04,800 345 00:15:04,800 --> 00:15:07,150 Which is mind blowing to me, because it's not just saying 346 00:15:07,150 --> 00:15:09,290 these things are along for the ride or that they might help 347 00:15:09,290 --> 00:15:10,070 us or hurt us. 348 00:15:10,070 --> 00:15:14,000 It's saying that we are-- 5-8% of our DNA 349 00:15:14,000 --> 00:15:16,390 actually comes from viruses. 350 00:15:16,390 --> 00:15:17,850 And this is another thing that speaks to 351 00:15:17,850 --> 00:15:19,720 just genetic variation. 352 00:15:19,720 --> 00:15:24,210 Because viruses do something-- I mean this is called 353 00:15:24,210 --> 00:15:27,760 horizontal transfer of DNA. 354 00:15:27,760 --> 00:15:30,480 And you could imagine, as a virus goes from one species to 355 00:15:30,480 --> 00:15:37,220 the next, as it goes from Species A to B, if it mutates 356 00:15:37,220 --> 00:15:41,310 to be able to infiltrate these cells, it might take some-- 357 00:15:41,310 --> 00:15:43,810 it'll take the DNA that it already has, that 358 00:15:43,810 --> 00:15:45,490 makes it, it with it. 359 00:15:45,490 --> 00:15:48,180 But sometimes, when it starts coding for some of these other 360 00:15:48,180 --> 00:15:52,830 guys, so let's say that this is a provirus right here. 361 00:15:52,830 --> 00:15:55,860 Where the blue part is the original virus. 362 00:15:55,860 --> 00:16:00,960 The yellow is the organism's historic DNA. 363 00:16:00,960 --> 00:16:04,230 Sometimes when it codes, it takes up little sections of 364 00:16:04,230 --> 00:16:07,200 the other organism's DNA. 365 00:16:07,200 --> 00:16:11,810 So maybe most of it was the viral DNA, but it might have, 366 00:16:11,810 --> 00:16:14,070 when it transcribed and translated itself, it might 367 00:16:14,070 --> 00:16:16,710 have taken a little bit-- or at least when it translated or 368 00:16:16,710 --> 00:16:18,460 replicated itself-- it might take a little bit of the 369 00:16:18,460 --> 00:16:20,540 organism's previous DNA. 370 00:16:20,540 --> 00:16:23,690 So it's actually cutting parts of DNA from one organism and 371 00:16:23,690 --> 00:16:24,950 bringing it to another organism. 372 00:16:24,950 --> 00:16:27,490 Taking it from one member of a species to another member of 373 00:16:27,490 --> 00:16:27,810 the species. 374 00:16:27,810 --> 00:16:29,750 But it can definitely go cross-species. 375 00:16:29,750 --> 00:16:32,860 So you have this idea all of a sudden that DNA can jump 376 00:16:32,860 --> 00:16:34,090 between species. 377 00:16:34,090 --> 00:16:36,410 It really kind of-- I don't know, for me it makes me 378 00:16:36,410 --> 00:16:39,930 appreciate how interconnected-- as a species, 379 00:16:39,930 --> 00:16:41,950 we kind of imagine that we're by ourselves and can only 380 00:16:41,950 --> 00:16:45,110 reproduce with each other and have genetic variation within 381 00:16:45,110 --> 00:16:45,860 a population. 382 00:16:45,860 --> 00:16:50,190 But viruses introduce this notion of horizontal transfer 383 00:16:50,190 --> 00:16:53,090 via transduction. 384 00:16:53,090 --> 00:16:57,640 Horizontal transduction is just the idea of, look when I 385 00:16:57,640 --> 00:17:00,660 replicate this virus, I might take a little bit of the 386 00:17:00,660 --> 00:17:04,349 organism that I'm freeloading off of, I might take a little 387 00:17:04,349 --> 00:17:06,010 bit of their DNA with me. 388 00:17:06,010 --> 00:17:09,160 And infect that DNA into the next organism. 389 00:17:09,160 --> 00:17:11,329 So you actually have this DNA, this jumping, 390 00:17:11,329 --> 00:17:13,119 from organism to organism. 391 00:17:13,119 --> 00:17:17,300 So it kind of unifies all DNA-based life. 392 00:17:17,300 --> 00:17:20,609 Which is all the life that we know on the planet. 393 00:17:20,609 --> 00:17:24,900 And if all of this isn't creepy enough-- and actually 394 00:17:24,900 --> 00:17:28,540 maybe I'll save the creepiest part for the end. 395 00:17:28,540 --> 00:17:30,800 But there's a whole-- we could talk all about the different 396 00:17:30,800 --> 00:17:31,670 classes of viruses. 397 00:17:31,670 --> 00:17:33,810 But just so you're familiar with some of the terminology, 398 00:17:33,810 --> 00:17:37,895 when a virus attacks bacteria, which they often do. 399 00:17:37,895 --> 00:17:41,150 And we study these the most because this might be a good 400 00:17:41,150 --> 00:17:42,630 alternative to antibiotics. 401 00:17:42,630 --> 00:17:45,430 Because viruses that attack bacteria might-- sometimes the 402 00:17:45,430 --> 00:17:47,820 bacteria is far worse for the virus-- but these are called 403 00:17:47,820 --> 00:17:49,070 bacteriaphages. 404 00:17:49,070 --> 00:17:52,610 405 00:17:52,610 --> 00:17:55,320 And I've already talked to you about how they have their DNA. 406 00:17:55,320 --> 00:17:57,890 But since bacteria have hard walls, they will just inject 407 00:17:57,890 --> 00:18:00,940 the DNA inside of the bacteria. 408 00:18:00,940 --> 00:18:06,630 And when you talk about DNA, this idea of a provirus. 409 00:18:06,630 --> 00:18:09,170 So when a virus lyses it like this, this is 410 00:18:09,170 --> 00:18:11,090 called the lytic cycle. 411 00:18:11,090 --> 00:18:13,760 This is just some terminology that's good to know if you're 412 00:18:13,760 --> 00:18:16,250 going to take a biology exam about this stuff. 413 00:18:16,250 --> 00:18:18,600 And when the virus incorporates it into the DNA 414 00:18:18,600 --> 00:18:22,350 and lays dormant, incorporates into the DNA of the host 415 00:18:22,350 --> 00:18:25,420 organism and lays dormant for awhile, this is called the 416 00:18:25,420 --> 00:18:28,030 lysogenic cycle. 417 00:18:28,030 --> 00:18:32,030 And normally, a provirus is essentially experiencing a 418 00:18:32,030 --> 00:18:35,910 lysogenic cycle in eurkaryotes, in organisms that 419 00:18:35,910 --> 00:18:38,250 have a nuclear membrane. 420 00:18:38,250 --> 00:18:40,890 Normally when people talk about the lysogenic cycle, 421 00:18:40,890 --> 00:18:44,750 they're talking about viral DNA laying dormant in the DNA 422 00:18:44,750 --> 00:18:45,600 of bacteria. 423 00:18:45,600 --> 00:18:48,600 Or bacteriophage DNA laying dormant 424 00:18:48,600 --> 00:18:51,050 in the DNA of bacteria. 425 00:18:51,050 --> 00:18:53,380 But just to kind of give you an idea of what this, quote 426 00:18:53,380 --> 00:18:59,480 unquote, looks like, right here. 427 00:18:59,480 --> 00:19:01,550 I got these two pictures from Wikipedia. 428 00:19:01,550 --> 00:19:02,800 One is from the CDC. 429 00:19:02,800 --> 00:19:11,360 430 00:19:11,360 --> 00:19:14,200 These little green dots you see right here all over the 431 00:19:14,200 --> 00:19:17,540 surface, this big thing you see here, this is a white 432 00:19:17,540 --> 00:19:20,330 blood cell. 433 00:19:20,330 --> 00:19:21,760 Part of the human immune system. 434 00:19:21,760 --> 00:19:23,050 This is a white blood cell. 435 00:19:23,050 --> 00:19:27,540 436 00:19:27,540 --> 00:19:31,060 And what you see emerging from the surface, essentially 437 00:19:31,060 --> 00:19:34,510 budding from the surface of this white blood cell-- and 438 00:19:34,510 --> 00:19:36,300 this gives you a sense of scale too-- 439 00:19:36,300 --> 00:19:39,700 these are HIV-1 viruses. 440 00:19:39,700 --> 00:19:46,970 And so you're familiar with the terminology, the HIV is a 441 00:19:46,970 --> 00:19:51,810 virus that infects white blood cells. 442 00:19:51,810 --> 00:19:54,890 AIDS is the syndrome you get once your immune system is 443 00:19:54,890 --> 00:19:55,900 weakened to the point. 444 00:19:55,900 --> 00:19:58,860 And then many people suffer infections that people with a 445 00:19:58,860 --> 00:20:01,450 strong immune system normally won't suffer from. 446 00:20:01,450 --> 00:20:03,050 But this is creepy. 447 00:20:03,050 --> 00:20:06,360 These things went inside this huge cell, they used the 448 00:20:06,360 --> 00:20:11,555 cell's own mechanism to reproduce its own DNA or its 449 00:20:11,555 --> 00:20:14,300 own RNA and these protein capsids. 450 00:20:14,300 --> 00:20:16,270 And then they bud from the cell and take a little bit of 451 00:20:16,270 --> 00:20:17,490 the membrane with it. 452 00:20:17,490 --> 00:20:20,990 And they can even leave some of their DNA behind in this 453 00:20:20,990 --> 00:20:22,340 cell's own DNA. 454 00:20:22,340 --> 00:20:25,280 So they really change what the cell is all about. 455 00:20:25,280 --> 00:20:26,890 This is another creepy picture. 456 00:20:26,890 --> 00:20:28,140 These are bacteriaphages. 457 00:20:28,140 --> 00:20:34,500 458 00:20:34,500 --> 00:20:36,110 And these show you what I said before. 459 00:20:36,110 --> 00:20:38,450 This is a bacteria right here. 460 00:20:38,450 --> 00:20:41,360 This is its cell wall. 461 00:20:41,360 --> 00:20:42,100 And it's hard. 462 00:20:42,100 --> 00:20:45,020 So it's hard to just emerge into it. 463 00:20:45,020 --> 00:20:47,040 Or you can't just merge, fuse membranes with it. 464 00:20:47,040 --> 00:20:52,290 So they hang out on the outside of this bacteria. 465 00:20:52,290 --> 00:20:55,410 And they are essentially injecting their genetic 466 00:20:55,410 --> 00:20:58,280 material into the bacteria itself. 467 00:20:58,280 --> 00:20:59,890 And you could imagine, just looking at the 468 00:20:59,890 --> 00:21:01,000 size of these things. 469 00:21:01,000 --> 00:21:02,090 I mean, this is a cell. 470 00:21:02,090 --> 00:21:04,350 And it looks like a whole planet or something. 471 00:21:04,350 --> 00:21:05,650 Or this is a bacteria and these 472 00:21:05,650 --> 00:21:06,620 things are so much smaller. 473 00:21:06,620 --> 00:21:08,170 Roughly 1/100 of a bacteria. 474 00:21:08,170 --> 00:21:10,570 And these are much less than 1/100 of this cell we're 475 00:21:10,570 --> 00:21:11,110 talking about. 476 00:21:11,110 --> 00:21:15,510 And they're extremely hard to filter for. 477 00:21:15,510 --> 00:21:16,520 To kind of keep out. 478 00:21:16,520 --> 00:21:20,780 Because they are such, such small particles. 479 00:21:20,780 --> 00:21:23,290 If you think that these are exotic things that exist for 480 00:21:23,290 --> 00:21:31,360 things like HIV or Ebola , which they do cause, or SARS, 481 00:21:31,360 --> 00:21:32,340 you're right. 482 00:21:32,340 --> 00:21:33,730 But they're also common things. 483 00:21:33,730 --> 00:21:35,490 I mean, I said at the beginning of this video that I 484 00:21:35,490 --> 00:21:36,300 have a cold. 485 00:21:36,300 --> 00:21:40,040 And I have a cold because some viruses have infected the 486 00:21:40,040 --> 00:21:42,610 tissue in my nasal passage. 487 00:21:42,610 --> 00:21:46,190 And they're causing me to have a runny nose and whatnot. 488 00:21:46,190 --> 00:21:48,540 And viruses also cause the chicken pox. 489 00:21:48,540 --> 00:21:50,550 They cause the herpes simplex virus. 490 00:21:50,550 --> 00:21:51,540 Causes cold sores. 491 00:21:51,540 --> 00:21:53,430 So they're with us all around. 492 00:21:53,430 --> 00:21:56,000 I can almost guarantee you have some virus 493 00:21:56,000 --> 00:21:57,740 with you as you speak. 494 00:21:57,740 --> 00:21:58,630 They're all around you. 495 00:21:58,630 --> 00:22:04,320 But it's a very 496 00:22:04,320 --> 00:22:06,480 philosophically puzzling question. 497 00:22:06,480 --> 00:22:09,090 Because I started with, at the beginning, are these life? 498 00:22:09,090 --> 00:22:11,495 And at first when I just showed it to you, look they 499 00:22:11,495 --> 00:22:13,740 are just this protein with some nucleic 500 00:22:13,740 --> 00:22:15,280 acid molecule in it. 501 00:22:15,280 --> 00:22:16,340 And it's not doing anything. 502 00:22:16,340 --> 00:22:17,780 And that doesn't look like life to me. 503 00:22:17,780 --> 00:22:18,610 It's not moving around. 504 00:22:18,610 --> 00:22:19,660 It doesn't have a metabolism. 505 00:22:19,660 --> 00:22:20,390 It's not eating. 506 00:22:20,390 --> 00:22:21,560 It's not reproducing. 507 00:22:21,560 --> 00:22:23,120 But then all of a sudden, when you think about what it's 508 00:22:23,120 --> 00:22:27,130 doing to cells and how it uses cells to kind of reproduce. 509 00:22:27,130 --> 00:22:29,700 It kind of like-- in business terms it's asset light. 510 00:22:29,700 --> 00:22:31,920 It doesn't need all of the machinery because it can use 511 00:22:31,920 --> 00:22:35,850 other people's machinery to replicate itself. 512 00:22:35,850 --> 00:22:38,080 You almost kind of want to view it as a 513 00:22:38,080 --> 00:22:39,520 smarter form of life. 514 00:22:39,520 --> 00:22:42,480 Because it doesn't go through all of the trouble of what 515 00:22:42,480 --> 00:22:44,110 every other form of life has. 516 00:22:44,110 --> 00:22:47,570 It makes you question what life is, or even what we are. 517 00:22:47,570 --> 00:22:51,510 Are we these things that contain DNA or are we just 518 00:22:51,510 --> 00:22:54,170 transport mechanisms for the DNA? 519 00:22:54,170 --> 00:22:56,260 And these are kind of the more important things. 520 00:22:56,260 --> 00:22:59,710 And these viral infections are just battles between different 521 00:22:59,710 --> 00:23:02,340 forms of DNA and RNA and whatnot. 522 00:23:02,340 --> 00:23:04,330 Anyway I don't want to get too philosophical on you. 523 00:23:04,330 --> 00:23:08,840 But hopefully this gives you a good idea of what viruses are 524 00:23:08,840 --> 00:23:12,940 and why they really are, in my mind, the most fascinating 525 00:23:12,940 --> 00:23:15,870 pseudo organism in all of biology. 526 00:23:15,870 --> 00:23:16,278