Viruses contain only one type of nucleic acid - either DNA or RNA Viruses can only replicate within living cells.
Some viruses also have a lipoprotein envelope.
CD4 receptor for HIV, ICAM-1 receptor for rhinoviruses, sialic acid residues as receptors for influenza Penetration of the cell may occur by endocytosis of intact virions or fusion of viral envelope with host cell membrane. Following viral DNA replication late viral genes are transcribed the products of which form the structural components of the virion. Errors for RNA viruses occur at a much higher rate eg. Cytopathic effects of virus infection Cell lysis eg. Inclusion bodies eg.