Friday, 7 February 2014

Are viruses alive?

Are viruses alive?

It is amazing how often I hear biologists say that a virus is not a living thing, but only a complex particle.  It is true that the simplest of viruses are nothing more than some DNA (or RNA) wrapped in protective layer of protein.

I think viruses deserve a better label than "complex particle".  

To begin to answer this question, we can start by looking at our list of the characteristics of life.  Viruses do share many of the characteristics of life:  viruses are ordered, they reproduce (however, they do need a host cell to do it), and they adapt from generation to generation (that's why we have new flu shot every year).  

Okay, that's not bad, but....  viruses do not process energy, show any sign of homeostasis, they don't really grow or respond to their environment.  Indeed, a virus is much like a very complicated chemical.  The chemical formula for the polio virus has even been worked out: C332652H492388N98245O131196P7501S2340 (source: Vincent Racaniello).  

It is true that unless a virus is inside a cell, it doesn't really do anything. 

They do not have all the characteristics of life, but how should we think about them?

However, it is not all that simple.  If viruses are not alive then:
In fact, when a virus enters a cell, it is certainly very active, and dare I say "alive".  It sheds its coat and takes over the entire operation of the cell (with the ultimate goal of making more viruses).  (There I go, talking about a virus having a "goal" - is it alive?).

We do know that viruses are parasites of life and that there is certainly a debate here that is worth exploring.  Many biologists will at least admit that viruses are indeed "lifeforms" that are a crucial part of the biosphere.  Most will admit that viruses exist in that murky milieu between life and everything else.

I will be writing a great deal about viruses in future posts.  If you want to read more about the question of viruses being alive, there is a good article here at Scientific American.

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