The NYT had a great piece last Tuesday about viruses and Swine Flu. Here's part of it:
"The current outbreak shows how complex and mysterious the evolution of viruses is. Some viruses use DNA, like we do, to encode their genes. Others, like the influenza virus, use single-strand RNA. But viruses all have one thing in common, said Roland Wolkowicz, a molecular virologist at San Diego State University: they all reproduce by disintegrating and then reforming.
A human flu virus, for example, latches onto a cell in the lining of the nose or throat. It manipulates a receptor on the cell so that the cell engulfs it, whereupon the virus’s genes are released from its protein shell. The host cell begins making genes and proteins that spontaneously assemble into new viruses. 'No other entity out there is able to do that,” Dr. Wolkowicz said. “To me, this is what defines a virus.'
The sheer number of viruses on Earth is beyond our ability to imagine. “In a small drop of water there are a billion viruses,” Dr. Wolkowicz said. Virologists have estimated that there are a million trillion trillion viruses in the world’s oceans. A tank of 100 to 200 liters of sea water may hold 100,000 genetically distinct viruses.
Viruses are diverse because they can mutate very fast and can mix genes. They sometimes pick up genes from their hosts, and they can swap genes with other viruses. Some viruses, including flu viruses, carry out a kind of mixing known as reassortment. If two different flu viruses infect the same cell, the new copies of their genes get jumbled up as new viruses are assembled."
Read the whole story:
http://www.nytimes.com/2009/05/05/health/05virus.html?_r=1&scp=1&sq=virus&st=cse
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