Monday, October 28, 2019

Characteristics of Viruses

Viruses are small obligate intracellular parasites, which contain a single type of nucleic acid (DNA or RNA) and a protein coat, sometimes enclosed by an envelope composed of lipids, proteins and carbohydrates. They are not cells or composed of cells.

The protein coat, or capsid, of an individual virion (fully assembled virus or virus particle) is composed of multiple copies of one or more types of proteins. These proteins assemble, forming structural units called capsomeres.

Biologists consider viruses to be non-living because:
*Are not cells
*Do not grow or respond to their surroundings
*Cannot make food, take in food, or produce wastes
*Viruses do not respond to stimuli.

They multiply by using the host cells synthesizing machinery to cause the synthesis of specialized elements that can transfer the viral nucleic acid to other cells.

Viruses are inert outside the host cell. Small viruses, e.g., polio and tobacco mosaic virus, can even be crystallized. Viruses are unable to generate energy. As obligate intracellular parasites, during replication, they fully depend on the complicated biochemical machinery of eukaryotic or prokaryotic cells. The main purpose of a virus is to deliver its genome into the host cell to allow its expression (transcription and translation) by the host cell.
Characteristics of Viruses
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