Virus Notes

Characteristics Tiny, non-living particle-not an organism One half to one-hundredth the size of the smallest bacterium Made of a protein coat and nucleic acid (DNA or RNA) Do not carry out respiration or grow or move Cannot reproduce without a host cell

Virus Structure

Viral Reproduction: Lytic Cycle Attachment: virus attaches to host Entry: injects nucleic acid into host Replication: host DNA is destroyed, new viral nucleic acid and proteins are made Assembly: new viruses are assembled Lysis and Release: host cell breaks open, dies, and releases new viruses into the organism to infect other cells

Lytic Cycle Diagram

Lysogenic Cycle Attachment: virus finds host Entry: injects nucleic acid Provirus formation: Viral nucleic acid becomes part of the host cell chromosome(s). Cell Division: Provirus is inactive & does not kill the host cell, but is replicated with the host chromosome(s) as the cell divides. Ex. Herpes, hepatitis B, chicken pox

Lysogenic Cycle Diagram

When “outbreaks” occur, lysogenic viruses go into the lytic cycle, make new viruses, and kill the host!!

An Exception….. Sometimes a provirus can make a few new viruses and release them by a kind of budding instead of killing the host cell. This occurs with influenza and HIV.

Retroviruses *Not all RNA viruses are retroviruses When retroviruses inject their RNA into host cells, they also inject the enzyme reverse transcriptase, which copies viral RNA into DNA before new viral parts are produced. Often, mistakes are made during the conversion, causing the virus to mutate. This is why new strains of flu come out every year! *Not all RNA viruses are retroviruses

Treatment of Viruses Viruses are usually treated by allowing the body’s immune system to take care of the infection Vaccines prevent diseases by helping the body’s immune system work faster and more effectively. Antiviral medications can help prevent viral infections or help the body recover faster if a viral infection is present. Vaccines and antiviral medications are used for treating specific diseases Antibiotics do not help viral infections!!!!