Viruses

Viruses Virus comes from the Latin word virus meaning poison What is a virus? A particle made of nucleic acid, protein, and sometimes lipids. Viruses are not members of the Six-Kingdom System of Classification Infect all taxonomic levels! They are highly specific

Viruses can reproduce only by infecting living cells. Enter cells and use the cell’s “machinery” to produce more viruses. Smaller than prokaryotic cells(can only be seen with an electron microscope) DNA or RNA core surrounded by a protein coat (capsid) Vary in size and shape

Groups of Viruses DNA Viruses Viroids Prions RNA Viruses Direct production of RNA Examples Herpes Pox RNA Viruses retrovirus Influenza Rhabdovirus (rabies) HIV Viroids Disease causing agent, RNA with NO capsid Examples Plant disease Prions Abnormal protein clumps, kills host Mad Cow Disease

Viral Infection Lytic Infection Virus enters cell, makes copies of itself, and causes cell to burst Lysogenic Infection Virus integrates its DNA into DNA of host cell, remains dormant and replicates when cell divides Viral DNA that attches to cell’s DNA is called prophage or provirus Enters lytic cycle when DNA removes itself from host DNA

Retroviruses RNA viruses Produce DNA from their RNA The DNA attaches to the host cell DNA and can be dormant for long periods HIV is an example

Are viruses alive? Viruses have many characteristics of living things Not cellular Only active in living cells Occupy a “gray” area between the living and non-living world