Viruses

Factual Questions
21

(I don’t really want to continue the hijack about viruses being alive but …

A lot of living things need something else to reproduce, grow, etc. I have no idea why viruses are treated any differently than other life forms. Even humans would be unable to live without all the bacteria living in our gut and elsewhere.)

So, taking viruses as alive as anything else, back to the OP.

Immortal? In the normal life cycle upon entering a cell a virus isn’t going to last much longer. The host cell is going to die and the virus is likely to speed up things. Rupturing of the cell wall usually results which allows the new copies to disperse.

If it never enters a host cell, it’s a lot like a dormant seed. Now, plant seeds can last a very long time under the right conditions. A virus is less fickle. So, easily thousands of years if things are just right. But immortal as in “Till the Sun expands and vaporizes the surface of the Earth”, I don’t think so. DNA/RNA even on virus scale will break down eventually, no matter how carefully it is naturally preserved.

Now, if you sequence it, carve the genome is a long lasting rock, bury it deep on the Moon, etc. Then you can resurrect it a billion years from now. But that’s still not the same as living forever.

22

yes, thanks!

23

Again, it’s a semantic issue of what constitutes “a living organism”. We generally reserve the term “alive” to an “organism”. So, is a virus an organism?

Well, no, it doesn’t quite meet the definition (or rather, it doesn’t have many of the characteristics). It does not ingest: it infects and appropriates host cell machinery, using what the host ingested. There are a number of similar criteria that viruses don’t meet.

But they’re definitely biological, and part of what we call “life”. They certainly have “active” and “inactive” phases. We can definitely think of “killing” it, as in “destroying” it, although this means a very different thing depending on whether it’s actively infecting, dormant infecting, or between hosts.

We use a lot of criteria to “define” what we call “life” that really might not apply to completely different (alien) lifeforms that were structured differently. But we have a hard time understanding even in theory how “life” could work without some kind of a boundary between inside the organism and outside it (e.g., cell membrane). This is one of the many hurdles that confounds the study of the origins of life. Was there some natural barrier that helped the first life define itself, or is it possible for life to begin to evolve without the barrier? no doubt the answer is a tricky combination of the two, and probably involving precursors that we wouldn’t quite call “life” but that meet some of the criteria.

24

Yes and no.

Yes, it’s a bit of a category error, but only due to the most commonly used definition of the term “living thing” or “being alive”.

That said, there’s definitely a reasonable way to interpret your question, with minor semantic adjustment. And the answer there is “No, a virus is not immortal. Or, it is, depending on what you think is the virus”

If you think of the virus as a whole, in its between-hosts form, well, it dies to reproduce. It loses its container. It’s component parts get distributed to different portions of the host cell. It ceases to exist as an individual.

But of course, it’s still infecting the host, and if I was the host, I’d definitely want to ‘kill’ that virus! So, … what’s “the virus”? Is it the specific crucial portion of DNA or RNA that it carries that causes the cell to create NEW copies of itself?

Note the difference here between a bacterial cell and a virus. A bacterial cell reproduces by fission. Is it immortal, since it lives on in its two daughter cells? The virus is less “immortal” than this, since it destroys itself in the process of making copies of itself. Frankly, the concept of identity falls apart here.

But the strain of virus continues to exist. Is that immortal? Again, depending on how you identify it. Are dinosaurs immortal, because we now have birds? Most folks would say they’re extinct. (But not xkcd!)

Based on the most common meanings of identity and immortality, the virus, even if we grant it as alive, doesn’t quite rate immortality.

On the other hand, an individual virus can last for incredibly long periods, even in rather harsh environments, in its encapsulated (between-hosts) form. Is a seed “alive” before it germinates? If it never germinates, but could?

25

Very good succinct points, learjeff, my mechanistic/empiricist viewpoint might describe a solar powered PC/3d printer coupled to a CAD/CAM machine as being life…
Returning to Bacteria what about Stromatalites?
Sorry need to return to BBC 3 who are running a Pink Floyd night, joys of living in London’
P

26

Stromatolites are just regular old bacteria that grew in mats that aggregated sediment and then those mats got fossilized. There are still stromatolites today, notably in Shark Bay in Australia, although they’re much more rare because there are so many organisms that can eat them than there were back in the Proterozoic.

27

Occasionally it’s nice to be astonished by Biodiversity, actually I’m constantly astonished by Life, thank you all.
Returns to BBC 3 and the Floyd.
Peter

28

ONLY some virus intentionally kill the host cell but the invidual virus is not killing itself. In fact the idea is that when the cell dies each virus from inside can go on to infect other cells.
Simple life forms can be preserved in eg freezing, or in amber perhaps. I wonder if a virus preserved in insects in amber may still be viable… Thats not actually immortal … it just means longer than normal. More complex life forms may be put in stasis too … not quite there yet for humans …

But what does this word immortal mean ? it implies that things that kill them don’t actually kill them. ( The old Dracula/Vampire can only be killed by a silver stake through the heart idea of immortal).

Immortal didn’t exist, so it is not a category error … well it is, because you moved fantasy to the real world. Immortal belongs to the category of fantasy fiction.

29

Or, as it turns out, to jellyfish.

Oh, all right, it’s not technically immortal, since most of them just get eaten. But it is deathless, in the sense that it cannot cease to live from old age. Theoretically.

30

I don’t think any virus does anything intentionally.

The original infecting virus is (in most cases, anyway) disrupted after it enters the cell, so it is reasonable to say that it dies (if it was ever alive). What is then subsequently released are many copies of the original, which can go on to infect further cells. Some of those copies may, perhaps contain some material from the original particle, but they are not the same individual virus.

I think the category error that the OP was afraid he might have made was in classifying viruses as alive in the first place. If something is not a living organism it makes no sense to ask if it could be immortal. As Learjeff hs rather nicely and carefully explained, there is, in fact, no very straightforward answer as to whether a virus is alive or not. However, as I already pointed out, even if we decide to say that a virus is alive, in no sense is it immortal. Virus particles can be disrupted and destroyed quite easily. (One might say, the only sort of immortality available to a virus is the same same sort that is also available to all types of living things, including us humans: i.e., through its offspring and their descendants over the generations. But, as Woody Allen almost said, “I don’t want to achieve immortality through my children; I want to achieve immortality by not dying.”)

31

Does a virus have sense organs? How does it detect when it’s near a viable cell to reproduce?

Does a virus move around under it’s own power? Where does the energy to do this come from?

I never considered these questions until this thread.

32

Cool, thanks! I had no idea.

I only know a little and only about a very few types of virus, so I’ll probably be overgeneralizing, but here goes.

A virus is basically one or more snippets of RNA and DNA enclosed in some kind of outer shell (“capsid”) made of proteins. The purpose of the capsid is to keep the stuff together and get it inside the host cell despite the cell’s defenses.

The RNA and DNA code for proteins that:

[ul]
[li] are parts of the capsid[/li][li] help assemble the virus[/li][li] affect normal cell behavior, overcoming cell defenses or providing the ‘exit’ strategy, which is often to have the cell kill itself (apoptosis)[/li][/ul] I bet that in some cases the RNA in the virus might also help with assembly.

Capsid complexity varies, but the most complex are a bit like fancy personalized mousetraps. They “fit” some feature on the outside of the host cell, and when they bump into it and the parts fit together, it triggers the mousetrap spring to inject the contents into the cell. (Or a gazillion other clever mechanisms, no doubt.)

The mechanism to detect the “fit” and react is a sort of sense “organ”, or at least, it might be similar to the detection mechanism of actual sense organs, stretching the definition a bit. But in general, viruses aren’t particularly active when outside the host. No doubt there are exceptions, as is the case with almost any statement about biology!

The “microbiology” section of the Wikipedia article on viruses gives a pretty good idea about the different types of structures, and how they reproduce. It doesn’t say much about the virus outside an infected host, and I suspect the reason is that there’s not much to say unless you get really technical and specific to particular viruses.

AFAIK, viruses don’t expend energy and don’t move around under their own power.

33

So what they’re saying is that if the old virus DNA that was inserted millennia ago is inactivated, fertilized eggs can’t implant and create a pregnancy, for at least three different mammals that we know of. Right? Cool.

But most of those things: 1) move under their own power or have some sort of process going on inside, 2) eat, 3) excrete, 4) can’t be crystallized and then uncrystallized without affecting their state.

I may have missed other crystallizable life forms. And as Learjeff explained, they don’t sense their environment nearly as much as they automatically lock onto and enter a cell if the chemistry of the cell membrane fits the chemistry of their capsule. It’s not so much an action that they take as a reaction that they’re a part of. So far as I’ve heard. Which would be a fifth thing that most life forms do that they don’t.

They’re cyanobacteria aka blue-green algae. Those are reeeeeally old life forms.

I think it’s pretty standard for the DNA of viruses to instruct the cell they infect to deconstruct its cell membrane, which kills it. Viruses that don’t do this are in danger of becoming a permanent part of the cell, rather than still being a virus.

34

Isaac Asimov once pointed out that this isn’t a very useful objection to viruses, since all life forms can be crystallized. Soldiers marching in rigid formation are an example of crystallized humanity.

And if you really want to blur the lines, there are examples of viruses that infect other viruses.

It’s like I keep on saying: Biology is much messier than the nice neat boxes we try to force it into.

35

I’m not a virologist or embryologist, but my understanding is that ancient retroviral envelope genes may have allowed the development of the placenta to evolve. Viruses have been around a lot longer than mammals.

[Retro]viral genomic RNA is reverse transcribed into DNA and integrated into the host genomic DNA. I believe it is estimated that 8-10% of our DNA is retroviral in origin. Retroviruses like HIV have gag, pol, and env genes along with others. The env genes allow fusion of cell membranes (from Wikipedia):

Wikipedia

So it is thought that fusion proteins encoded by ancient retroviral env genes now help form the syncytiotrophoblast by merging cells with a single nucleus into syncytia. A syncytium is a multinucleated cell.

At least that is how I understand it.
An aside.

From that link:

I once heard a talk by Koonin and he was the worst speaker I have ever had to listen to. Said “Oom” probably half a dozen times in each and every sentence and spent the first half hour standing between the projector and screen. The middle sections of his slides were projected on his shirt. After he realized this, he said: “Well, I don’t want to be immaterial”. Smart guy though, but the seminar was painful.