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Virus (life science) - MSN Encarta (2021 words) |
 | Viruses are between 20 and 100 times smaller than bacteria and hence are too small to be seen by light microscopy. |
| Viruses are not considered free-living, since they cannot reproduce outside of a living cell; they have evolved to transmit their genetic information from one cell to another for the purpose of replication. |
| Viruses that infect through the respiratory tract are usually transmitted by airborne droplets of mucus or saliva from infected individuals who cough or sneeze. |
| virus. The Columbia Encyclopedia, Sixth Edition. 2001-05 (922 words) |
| Many viruses have striking geometrically regular shapes, with helical structure as in tobacco mosaic virus, polyhedral (often icosahedral) symmetry as in herpes virus, or more complex mixtures of arrangements as in large viruses, such as the pox viruses and the larger bacterial viruses, or bacteriophages. |
| In viruses with a membrane envelope the nucleocapsid (capsid plus nucleic acid) enters the cell cytoplasm by a process in which the viral envelope merges with a host cell membrane, often the membrane delimiting an endocytic structure (see endocytosis) in which the virus has been engulfed. |
| Viruses are not usually classified into conventional taxonomic groups but are usually grouped according to such properties as size, the type of nucleic acid they contain, the structure of the capsid and the number of protein subunits in it, host species, and immunological characteristics. |
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