Thread: Why do virusses exist?

This may be a strange question, but why do virusses actually exist? Should I see them as a sort of animal, that wants to survive? I thought this was the case for bacteria, but not for virusses. Or maybe I should rephrase the question: where did virusses originally evolve from?

Think of viruses as a small collection of genes that want to replicate themselves to make more viruses.
Bacteriophage (the viruses that infect bacteria) are actually really interesting and a lot is known about phage genetics. When studying their life cycles it becomes fairly clear that all they do is either infect the cell and use it as a tiny "phage factory" to make hundreds of copies of iltself ... or infect the cell, insert into the DNA and wait until a better time to turn the bacteria into a "phage factory".

Pretty much all a virus actually is i either DNA or RNA with a little protein shell.

Originally Posted by sigmafactor

Think of viruses as a small collection of genes that want to replicate themselves to make more viruses.
Bacteriophage (the viruses that infect bacteria) are actually really interesting and a lot is known about phage genetics. When studying their life cycles it becomes fairly clear that all they do is either infect the cell and use it as a tiny "phage factory" to make hundreds of copies of iltself ... or infect the cell, insert into the DNA and wait until a better time to turn the bacteria into a "phage factory".

Pretty much all a virus actually is i either DNA or RNA with a little protein shell.

yeah viruses are just as desperate to survive and multiplate as anything else

I think we could start thinking about ourselves as viruses. And looking at Earth like it was a yummy human. Well, maybe we already have.

...I've always thought of phages as the pirates of the microscopic world...

dunno why. It origionally had to do with some long, drawn out, and ridiculous analogy involving the comandeering of bacteria, I think...

-Ajain

Argument continues over whether viruses are truly alive. According to the United States Code, they are considered to be micro-organisms in the sense of biological weaponry and malicious use. Scientists however are more divided. They have no trouble classifying a horse as living, but things become complicated as they look at the more simple viruses, viroids and prions. Viruses resemble life in that they possess nucleic acid and can respond to their environment in a limited fashion. They can also reproduce by creating multiple copies of themselves through simple self-assembly.

However, unlike all established types of lifeform, they do not possess a cell structure, regarded as the basic unit of life. Viruses are also absent from the fossil record, making phylogenic relationships difficult to infer. Additionally, although they reproduce, they do not metabolise on their own and therefore require a host cell to replicate and synthesise new products. However, confounding this previous statement is the fact that bacterial species such as Rickettsia and Chlamydia, while living organisms, are also unable to reproduce outside of a host cell.

An argument can be made that all accepted forms of life divide at the cell level via cell division to reproduce, whereas all viruses assemble spontaneously within cells. The comparison is drawn between viral self-assembly and the autonomous growth of non-living crystals. Virus self-assembly within host cells also has implications for the study of the origin of life, as it lends credence to the hypothesis that life could have started as self-assembling organic molecules.

Other questions involve the classification of viruses within the evolutionary tree and its implications – if viruses are considered alive, then the criteria specifying life will have been permanently changed, leading scientists to question what the basic prerequisite of life is. If they are considered living then the prospect of creating artificial life is enhanced, or at least the standards required to call something artificially alive are reduced. If viruses were said to be alive, the question could follow of whether other even smaller infectious particles, such as viroids and prions, would next be considered forms of life.

Discussing the question of whether or not viruses are 'alive' is strictly semantic.

Think of it this way. The word 'alive' was borrowed from layspeak and lacks the precision required for true scientific discussion.

The question of whether viruses live or not depend upon how you want to split hairs.

As to why...
Why not?


As to "where did virusses originally evolve from?"

Who knows? There are theories that they escaped from living cells.
I personally favor this view.
As soon as a chunk of genome evolves which can package itself and seek a new host... voila. Virus is born.

There are jumping genes within the genome called 'transposons'. These genes are known to move about within the genome. Inhabiting it like a host. These might have been first steps along the route to the creation of the virus.

Or maybe they're remnants of earlier virus infection?

Virus infections might play a huge role in evolution. Retroviruses remain in your genome (of the cells they infect) until cell death. If they infect germ line cells....

Vioruses do exist cause some genes along time ago escaped the cells and began replicating on their own

virus do not have exobiological live. They just can live (multiplicate) in others organisms.
Same go for the prions and alike.

Same go for the prions and alike.

I find this to be a very odd statement.
Prions are just misfolded proteins. You'd have to stretch the definition of 'alive' quite far to even think about bringing the subject of prions into the discussion....

Originally Posted by invert_nexus

Same go for the prions and alike.

I find this to be a very odd statement.
Prions are just misfolded proteins. You'd have to stretch the definition of 'alive' quite far to even think about bringing the subject of prions into the discussion....

Yep but they have the ability to replicate in a certain way. In my classication there is real life : bacteria, cells and alike. There is also a lesser form of life that I call the endobiological live : organisms that can only live within other organisms (read cell, bacteria, protozoarius ...)

The second form of life canno't exist without the first one, and appeared later

Yep but they have the ability to replicate in a certain way.

Not... really.
Let's say a cell is infected with a prion. This prion doesn't cause the cell to start manufacturing the protein which misfold into the prion. It merely causes the proteins, if they are created by that cell, to misfold in a like manner to the prion.

The question of why is a damned interesting one and should inform us of cellular mechanics in many ways. But, it's not what I would term replication.

The second form of life canno't exist without the first one, and appeared later

I agree that viruses probably came later. Breakouts from normal life forms.

However, there is a distinct possiblity that they arose hand in hand. It's quite possible that the genetic command structures came after the metabolic machinery. Before the cell was integrated as a whole, it's possible that genetic material merely moved around hijacking this or that metabolic machinery in order to replicate itself.

Origins of life are quite unclear at the moment.


By the way, some viruses do contain some metabolic machinery. For instance, the retrovirus contains a reverse trancriptase.

Not... really.
Let's say a cell is infected with a prion. This prion doesn't cause the cell to start manufacturing the protein which misfold into the prion. It merely causes the proteins, if they are created by that cell, to misfold in a like manner to the prion.

The question of why is a damned interesting one and should inform us of cellular mechanics in many ways. But, it's not what I would term replication.

Exactly, that's why I said in a certain way. It's not relly duplication, but I did not find a proper name for this process of mutation who leads to a copy.

The second form of life canno't exist without the first one, and appeared later

I agree that viruses probably came later. Breakouts from normal life forms.

However, there is a distinct possiblity that they arose hand in hand. It's quite possible that the genetic command structures came after the metabolic machinery. Before the cell was integrated as a whole, it's possible that genetic material merely moved around hijacking this or that metabolic machinery in order to replicate itself.

Origins of life are quite unclear at the moment.


By the way, some viruses do contain some metabolic machinery. For instance, the retrovirus contains a reverse trancriptase.

You are right, my studies in microbiologia are starting to get old : almost twenty years ...

[quote="invert_nexus"]

By the way, some viruses do contain some metabolic machinery. For instance, the retrovirus contains a reverse trancriptase.

I don't think this is what the poster meant by metabolism. Metabolism is what cells do to store/release energy.

Reverse transcriptase is simply a molecular tool that facilitates the survival/replication of the viral RNA.

Originally Posted by Pendragon

This may be a strange question, but why do virusses actually exist? Should I see them as a sort of animal, that wants to survive? I thought this was the case for bacteria, but not for virusses. Or maybe I should rephrase the question: where did virusses originally evolve from?

Since I once heard somebody say "All questions can be answered with a yes or no", I'll answer your questions (in order)as follows;

Yes,

and to your second question, possibly.

Seriously the question "Why does x or y or z exist" is irrelevant, since it was not built by man, looking for the reason for existence when reason is a quality of man, not the universe. Other than man-made things, everthing exists, because all it's constituent parts fell into place. And now my head hurts!

Wow some really interesting answers! Thanks, I learned a lot :wink:

Originally Posted by billco

Seriously the question "Why does x or y or z exist" is irrelevant, since it was not built by man, looking for the reason for existence when reason is a quality of man, not the universe. Other than man-made things, everthing exists, because all it's constituent parts fell into place. And now my head hurts!

True, but I rephrased it into a relevant question. No need to hurt your head about that :P

Hmm.
After going back through this thread after being made aware of Fausto's obfuscatory ways and seeing a rather clearly worded post... I googled his post and guess what I found?

http://en.wikipedia.org/wiki/Virus

Now. Wikipedia is open source, but it's not really ethical to not link to the source of a complete cut and paste.

Lame.

Originally Posted by Pendragon

Wow some really interesting answers! Thanks, I learned a lot :wink:

Originally Posted by billco

Seriously the question "Why does x or y or z exist" is irrelevant, since it was not built by man, looking for the reason for existence when reason is a quality of man, not the universe. Other than man-made things, everthing exists, because all it's constituent parts fell into place. And now my head hurts!

True, but I rephrased it into a relevant question. No need to hurt your head about that :P

Strange that, I singularly failed to spot or answer the third question, had I seen it I probably wouldn't have posted, I have no idea of the answer.