Viruses are small intracellular parasites that invade the cells of virtually all known organisms. They reproduce by utilizing the cell's machinery to replicate viral proteins and genomic material, generally damaging or killing the host cell in the process; subsequentelly, a large number of newly generated viruses go on to infect other cells. Viruses are responsible for a wide variety of human diseases, ranging from the common (influenza and colds) to the exotic (AIDS, West Nile virus and Zika). Some viruses which are not dangerous to humans can also be exploited in technological applications, in addition, viruses find use in genetic engineering applications and increasingly in the design of new nanomaterials. At the very least, all viruses contain two components: the capsid (a protein shell), and a genome, consisting of either DNA or RNA. Some viruses also include accessory proteins to aid in infection, and in some cases a lipid bilayer to further protect their contents from the environment. The viral life cycle itself is deceivingly simple: viruses enter the cell, typically (but not always) through the interaction of their capsid with a receptor on the cell surface; the virus must then somehow disassemble its capsid to release its genetic material and any necessary helper proteins. The viral genome is then replicated and the proteins it codes for are synthesized to produce the raw material for the production of new viral particles; these new viruses then assemble and bud from the cell either through the membrane or upon cell death.
Spotlight: Simulating an Entire Life Form (Mar 2006)
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Viruses, the cause of many diseases, are the smallest natural organisms known. They are extremely primitive and parasitic such that biologists refer to them as "particles", rather than organisms. Viruses contain in a protein shell, the capsid, their own building plan, the genome, in the form of DNA or RNA. Viruses hijack a biological cell and make it produce from one virus many new ones. Viruses have evolved elaborate mechanisms to infect host cells, to to produce and assemble their own components, and to leave the host cell when it bursts from viral overcrowding. Because of their simplicity and small size, computational biologists selected a virus for their first attempt to reverse-engineer in a computer program, NAMD, an entire life form, choosing one of the tiniest viruses for this purpose, the satellite tobacco mosaic virus. As described in a recent report, the researchers simulated the virus in a small drop of salt water, altogether involving over a million atoms. This provided an unprecedented view into the dynamics of the virus for a very brief time, revealing nevertheless the key physical properties of the viral particle as well as providing crucial information on its assembly. It may take still a long time to simulate a dog wagging its tail in the computer, but a big first step has been taken to simulate living organisms. Naturally, this step will assist modern medicine (more on our satellite tobacco mosaic virus web page).