Viruses

-a virus is a Non-cellular particle made of genetic material and proteins that invade living cells

Characteristics Microscopic Genetic makeup – DNA or RNA (never both) No nucleus (not a prokaryote) Not a cell Can only reproduce inside living cells Parasite – depends on other organisms for life, thus causing them harm( host range) host specific Viruses are not alive

Virus Structure -all viruses contain a Capsid- outer protein coat containing nucleic acid -some viruses contain an envelope surrounding the capsid. **

Capsid

Virus Types Animal, Plant, Bacteria

Bacteria Phage Replication -Lytic cycle (Virulent phage) – The virus uses host DNA to build more virus structures in side the cell. Then the infected cell bursts (lyses) and releases the virus.

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Viral Replication -Lysogenic Cycle (temperate phage)- virus nucleic acid combines with host nucleic acid forming a prophage. It lays dormant as host cell divides. After a period of time it goes into the lytic cycle. -Prophage- phage and cell nucleic acid combined

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Animal Viruses 5 classes

HIV Reproduction Uses reverse transcriptase to turn RNA into DNA (retrovirus) Different from phages because it buds out.

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Viral Vectors -People -Touch (objects) -Airborne -Waterborne -Mosquito borne

Viruses and Disease -Epidemic- a general out break of a virus. -Pandemic- a global outbreak (spanish flu 1918) 500,000 dead in the US in 25 weeks, more that aids has killed in 25 years. More that the black plague in 4 years. More than WWI I had a little bird, Its name was Enza. I opened the window, And in-flu-enza

Protection Restriction enzymes- enzymes that splice DNA. Bacteria use them to splice viral DNA. Vaccines- a variant form of the virus given to allow the immune system to develop antibodies Some medicines target viral enzymes like reverse transcriptase in HIV

Viral Evolution Viroids- a small circular RNA moecule that infects plants. They use the host enzymes to replicate

Evolution con’t Prions- misfolded infectious brain proteins that change the shape of hosts brain proteins. (mad cow disease) Act slowly for up to ten years before symptoms develop and are almost indestructible.