REPRODUCTION OF VIRUSES

Reproduction of Viruses

 The structure of viruses allows them to succeed in their main mission—reproduction.

 Lytic Cycle

 Once attached to a host cell, a virus injects its nucleic acid into the cell. The nucleic acid takes over the normal operation of the host cell and produces multiple copies of the virus’s protein coat and nucleic acid. Once produced, the protein coats and the nucleic acids are assembled into new viruses. As the host cell fills with newly assembled viruses, it bursts, just like a balloon with too much air. The host cell then dies, and the released viruses begin searching for the next host cell. This type of viral reproduction is called a lytic (LIT ihk) cycle. The steps of a lytic cycle for a bacteriophage are illustrated in Figure.

 Lysogenic Cycle

 Some viruses, such as herpes and HIV, enter the host cell but remain hidden for years. Even though the viral nucleic acid becomes part of the host cell’s chromosome, it does not seem to affect the functions of the cell. At some point, however, the viral nucleic acid becomes active. It separates itself from the host cell’s genetic material, takes over the functions of the cell to produce new viruses, and destroys the host cell as the new viruses are released. This type of viral reproduction is called a lysogenic (li suh JE nihk) cycle. The steps of a lysogenic cycle are also shown in Figure.