Viruses:
OVERVIEW
Obligate intracellular agent which ,depend on host in their replication ,composed of nucleic acid core (DNA or RNA) surrounded by a protein coat.
The viruses are:
1- The smallest infectious agents ranging from about 20-300nm in diameter. 2- They are all potentially infectious. 3- The viruses are presence of a single nucleic acid, absence of enzymes for energy, metabolism and absence of ribosomes. 4- They are obligate parasites; also they can be reproduce, living, growth inside living cells by using cellular synthesis machinery. 5- Most of viruses infect specific host cells that are due to specific attachment sites on the host cells called receptors.
