Viruses
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LearningTranscript
00:00What is wrong with you?
00:16Dear Rita and Moby, are viruses alive?
00:19From Aiden.
00:20Oh, that's what your problem is.
00:28Computer viruses aren't alive, but the ones that make us sick are.
00:40Well, not really.
00:43I mean, kinda?
00:45The thing is, viruses share some of the qualities of living things, but they also lack some
00:51really important ones.
00:53If you ask a bunch of biologists this question, you won't get an answer.
00:58You'll get an argument.
01:02Viruses are teeny tiny particles that invade living things.
01:06Once inside, they multiply like crazy, creating an infection, which can sicken the host, the
01:12organism they infect.
01:14At some point during the infection, the host becomes contagious, able to spread the virus
01:20to new victims.
01:23Viruses can't move on their own, though.
01:25They need help getting around.
01:27Some are carried by animals, like mosquitoes.
01:30Others spread through contact with bodily fluids, like blood or saliva.
01:34Or by getting launched into the air by a sneeze or a cough.
01:38Whenever you get a cold, you're playing host to a virus.
01:42Flues are caused by viruses, too.
01:44So are some deadlier diseases like AIDS and polio.
01:49But many viruses are harmless to us.
01:52They just hang around inside our bodies and we never even know it.
01:55It all depends on the type of virus.
02:03In a way, a virus is like a very simple version of a cell.
02:07At its center is a strand of genetic code.
02:10That's the instructions for making copies of itself.
02:13It carries these molecules within a protective shell called a capsid.
02:18Around that, some viruses have another layer called an envelope.
02:21And the outer layer is studded with these spiky things for breaking into cells.
02:27That's about it.
02:28They're just a package of instructions with no tools to carry them out.
02:32Which is why viruses need to infect cells.
02:36So they can use the special machinery inside to multiply.
02:40They can do that because every virus's genetic code is made of either DNA or RNA,
02:46which are the same molecules that cells use to carry information and send messages.
02:52Things like build this structure or divide in two.
02:55But when a virus invades a cell, its genetic code sends out a new message.
03:00Build more of this virus.
03:02The cell listens because the virus is speaking its language.
03:06Yup, building viruses can prevent the cell from doing its job.
03:12Plus, those freshly made viruses may bust out of the cell and destroy it.
03:17That's part of how infections can make us sick.
03:20It takes a while for our immune systems to learn how to identify the invaders.
03:25But once it does, it fights off the infection by destroying every one of them.
03:30Vaccines, medicines that prevent viral infections, jumpstart this process.
03:36They teach your immune system how to identify a virus without making you sick.
03:41Once you've been vaccinated or infected, your immune system will remember what the virus looks like.
03:47Specifically, those spikes viruses use to break into cells.
03:52They fit into slots on the host cell's surface, kind of like a lock and key.
03:58Each virus only has the key to the cells of certain organisms.
04:02It's host species.
04:04That's why when you're sick with a cold, you don't have to worry about spreading it to your dog.
04:09But that doesn't mean your dog's totally off the hook.
04:12Because as far as we know, there are specific viruses for every living thing on the planet.
04:17All plants, animals, fungi, algae, even single-celled organisms like bacteria get infected by viruses.
04:28Ahem.
04:30Right, so occasionally, a virus can gain access to a new host species.
04:37Cells crank out thousands of viruses, and things don't always go perfectly.
04:42When the cell copies the virus's genetic code, it sometimes makes mistakes.
04:47Most of these mutations don't affect the virus.
04:51Some will harm it, but in rare cases, a mutation gives the virus a new ability.
04:57If it changes the shape of that key molecule, the virus might gain the ability to infect a new kind of cell.
05:05That's how a virus can suddenly start infecting a new kind of host.
05:09Like the one that causes COVID-19.
05:12It was a bat virus before it mutated and made the jump to people.
05:17Once a virus gets a helpful mutation, it'll be more likely to achieve its mission of copying itself.
05:23It'll pass on that new mutation and all the advantages that come with it.
05:28This process of passing genetic changes on to the next generation is known as evolution.
05:34And viruses evolve faster than any organism on Earth.
05:39Yup, that's the secret to their world domination.
05:43Our planet is absolutely covered in viruses.
05:47They're just so tiny that no one noticed their everywhere-ness until recently.
05:53We're talking like 10 times smaller than the average bacterium.
05:57So small, light waves can't bounce off them, making them basically invisible.
06:04But stack up every virus on the planet,
06:08they'd stretch out of Earth's atmosphere,
06:12past the moon,
06:14out of the solar system,
06:16out of the galaxy,
06:18millions and millions of light years long.
06:24Well, they can evolve thanks to their genetic code.
06:28And they can reproduce.
06:30All arguments that viruses are a form of life.
06:34But they can't reproduce on their own.
06:36They're not made of cells.
06:38They don't grow or regulate their bodies.
06:40They don't even use energy, or respond to their environment,
06:44or do anything until they infect a cell.
06:46Which doesn't sound very alive to me.
06:49They're more like pieces of life's machinery that somehow got loose in the world.
06:55The problem is, we humans like to put everything in neat little categories.
07:00Like, this is a planet, and this isn't.
07:04This food's healthy, and this one's not.
07:08This critter's alive, and this thing's not.
07:12But nature usually isn't so neat.
07:18Rude?