Educator

Viral Structure and Genetics

• Viruses consist of nucleic acid enclosed in a protein capsid. Some viruses are covered by an envelope derived from the host cell membrane.
• Viruses cannot reproduce independently. To reproduce, they must infect a host cell and use the host cell's machinery to produce viral nucleic acids and proteins.
• Phage may reproduce either via the lytic cycle or the lysogenic cycle.
• During the lytic cycle, the virus attaches to the host cell and then injects its genetic material. A viral enzyme degrades the host DNA and the host cell's machinery is used to synthesize viral nucleic acids and proteins. The phage self-assemble and the bacterial cell is lysed to release the newly produced phage.
• During the lysogenic cycle, phage DNA integrates into the bacterial genome and is replicated along with the bacterial DNA. An environmental cue, such as UV light, can trigger the phage to be excised from host DNA and enter the lytic cycle.
• Positive sense RNA viruses contain RNA that can be translated directly into a protein. Negative sense RNA viruses contain RNA that serves as a template for the synthesis of mRNA.
• Retroviruses synthesize complementary DNA (cDNA) from an RNA template using the enzyme reverse transcriptase. HIV is a retrovirus.