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Capsid based life
Topic Started: Nov 19 2009, 10:10 PM (894 Views)
Paul_de_Vries
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I personally see viruses as a kind of life even though many many many people disagree. This is because I find the definition of life extremely arbitrary and biased towards more familiar forms of life that were known to us earlier; if viruses had been studied before bacteria (I know I know...its just a thought experiment), then a definition of life would have been made to include viruses. Maybe (according to the prevailing definition) viruses were even alive once, but degenerated into non-life long ago as they specialized in parasitism of cellular life.

Anyway what I wanted to ask your opinion about is this: viruses aren't celular... instead they have a protein coat called a capsid. There is actually a virus which is bigger than some prokaryotes (both in actual size, and genome size).

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

So... what about a form of life which developed into the capsid equivalent of multicelular organisms. Is it plausible? In any way? We tend to consider viruses inferior to cellular life...but maybe thats the wrong way to look at it. They have no need to become more advanced, they are great at their way of life. Maybe if they wouldnt have gone down this path, they could have become just as advanced as cellular life is on earth.
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Holben
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Rumbo a la Victoria

Unless they expanded into space.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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sam999
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Parasky
Nov 21 2009, 01:11 PM
Holbenilord
Nov 21 2009, 05:46 AM
But with a thick protein coat, it would be hard for nutrients to get into cells.
My point exactly. It just seems too inefficient from an evolutionary point of view. The only way it would be able to survive and not be out-competed by other, more efficient organisms is if it reproduced at an ungodly rate, at which point overpopulation would spell disaster for the ecosystem and doom for the species.
If evrything breeds fast and most young die that works too.
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Holben
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They'd use up the biomass of the planet in super-time.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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Paul_de_Vries
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Quote:
 
But with a thick protein coat, it would be hard for nutrients to get into cells.


Really? Because right now the way a large percentage of nutrients get into our cells is by protein channels. I don't think a protein membrane (capsid) is more inefficient at all (or atleast not in any obvious way). I think the main problem lies in that the lipid membrane is easier to evolve, and hence would have already fortified the niches they occupy before that capsid evolved, giving them little chance. In my opinion thats why capsid based life is restricted to the virus role here on earth.

You have to remember that there are many different types of membranes present in cellular life in addition to the plasma membrane. I'm not saying the plasma membrane is a "frozen accident" because obviously its good at what it does, but rejecting anything that isnt plasma membrane based just because they are so succesful here on earth is too restricting. The conditions on earth favoured the dominance of the plasma membrane, but the conditions on another planet might favor something entirely different.

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Holben
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Well on another planet lichens could be dominant. In a parallel universe, earth is ruled by capsid based life.
Time flows like a river. Which is to say, downhill. We can tell this because everything is going downhill rapidly. It would seem prudent to be somewhere else when we reach the sea.

"It is the old wound my king. It has never healed."
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