Virii Essay, Research Paper

Viruses

are not truly alive. They

are much smaller and less complex than cells. Most

viruses multiply exclusively inside living host cells. Viruses

cause disease by the sum of the effects of damage to the host cells they

invade and the effects of toxins which are produced in the process. They

are DNA or RNA in a protein coat (capsid). They

have no nucleus, cytoplasm, or membranes. They

do not carry out cellular functions. Viruses

contain very few enzymes and so, as intracellular parasites, they uses the

host?s enzymes for their own metabolism. Viruses

are unable to move and so rely on passive dispersal, or a vector, to move

them between host cells. Viruses

reproduce by binding to specific cells, penetrating the cell membrane and

then using the protein making machinery (transcription and translation) of

the cell to build fresh viruses. DNA

viruses, e.g. smallpox, do not mutate and can be transcribed directly. RNA

viruses, e.g. AIDS, mutate regularly – have to be reverse-transcribed back

to DNA.