When it comes to viruses, the definition of ‘living’ and ‘non-living’ becomes a complicated issue. Some would argue that merely having a protein coat and genetic material does not qualify a living thing. However, when we look at virus' structural variety and incredible ability to replicate in a wide range of hosts, it is undeniable that they are indeed responding to their environment and evolving alongside other life forms.
Viruses have viral receptor proteins on their surface, which recognize specific host cells. They then insert their genetic material into the cell, and either create additional copies of their genome on their own (in the case of RNA viruses), or rely on the host cell’s machinery (DNA viruses) for the same purpose. Of course, the host cell has its own ways of recognizing these foreign invaders. A method called RNA interference cuts off the production of viral mRNA, hindering the reproductive cycle. In humans, killer T-cells recognize viral fragments on the surface of an infected cell and mark it for apoptosis. Interestingly, the HIV virus undergoes rapid mutations that change the amino acid sequence on its viral coat, enabling it to escape both vaccines and the killer T-cell response.
Researchers at Imperial College London have recently captured a new video of the vaccinia virus spreading throughout cells over the course of 16 hours. The virus appears to spread at a faster rate than its replication cycle allows; it apparently has evolved a mechanism which allows it to recognize which host cells have and have not yet been infected, thereby saving time and effort. This new information could change the way we approach viral propagation, and hopefully, it will lead to more advanced medical strategies in treating viral diseases.
Reference: Video of virus in action shows viruses can spread faster than thought possible
Image: Electron micrograph of a vaccinia virus. Can be found here.
Linda Le is a contributing writer on biomedical research to TuftScope for Spring 2010.
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