Diagram of a Retrovirus
Illustration of the structure of a retrovirus.
Retroviruses are infectious particles consisting of an RNA
genome packaged in a protein capsid, surrounded by a lipid
envelope. This lipid envelope contains polypeptide chains including
receptor binding proteins which link to the membrane receptors of
the host cell, initiating the process of infection.
Retroviruses contain RNA as the hereditary material in place of the more
common DNA. In addition to RNA, retrovirus particles also contain the enzyme
reverse transcriptase (or RTase), which causes synthesis of a complementary
DNA molecule (cDNA) using virus RNA as a template.
When a retrovirus infects a cell, it injects its RNA into the cytoplasm
of that cell along with the reverse transcriptase enzyme. The cDNA produced
from the RNA template contains the virally derived genetic instructions
and allows infection of the host cell to proceed.
The virus that causes AIDS (acquired immune deficiency syndrome)
is a retrovirus. It is called HIV for human immunodeficiency