getyourowncoat

A virus is a sub-microscopic contagious agent that is unable to grow or reproduce outside a mass cell. Each viral atom, or virion, consists of genetic material, DNA or RNA, within a protective protein coat called a capsid. The capsid shape varies from simple helical and icosahedral (polyhedral or near-spherical) forms, to more complex structures with tails or an envelope. Viruses infect cellular life forms and are grouped into animal, plant and bacterial types, according to the type of host infected.

It has been argued whether viruses are living organisms. Some consider them non-living as they do not meet the criterion of the definition of life. For example, unlike most organisms, viruses do not have cells. However, viruses have genes and progress by natural selection. Others have described them as organisms at the edge of life. Viral infections in human and animal hosts usually result in an impervious response and disease. Often, a virus is completely eliminated by the impervious system. Antibiotics have no effect on viruses, but antiviral drugs have been developed to treat life-threatening infections. Vaccines that produce lifelong resistance can prevent virus infections.

# posted by JANET ROSE @ 7:15 AM 0 comments