virus is a microscopic infectious agent that is unable to grow or reproduce out side a host cell. Virus infects all cellular life and now more than 5001 types of virus has been described.
STRUCTURE OF VIRUS
Virus consists of two parts the upper portion is head portion and the lower portion is body portion. All viruses have genes made from either DNA OR RNA long molecules that carry genetic information. All have a protein coat that protects these genes. Viruses are about 100 times smaller than bacteria.
LIVING VIRUS
Virus contains only RNA & DNA but never both.
They reproduce at a very high rate but only in living host cells.
Viruses are intracellular parasites.