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Virus Virus • biological particle/ pathogen • virus comes from Latin “poison” • living? or non-living? rabies virus Virus Virus Virus First virus • Wendell Stanley (1935) • studying splotchy leaves on tobacco • discovered and isolated tobacco mosaic virus (TMV) Virus Structure of a Virus • nucleic acid core (DNA or RNA), surrounded by outer protein coat called a capsid • different shapes: hellical (rod), sperical, polyhedral, different sizes 17nm – 100nm • some have an envelope with spikes that surrounds the capsid • contain no cell organelles, carry out no metabolic reactions • reproduce only inside a host cell • many are host specific • classified by type of nucleic acid and shape Virus Structure of a Virus • nucleic acid core (DNA or RNA), surrounded by outer protein coat called a capsid Structure of a Virus • different shapes: hellical (rod), sperical, polyhedral, different sizes 17nm – 100nm Virus Structure of a Virus • some have an envelope with spikes that surrounds the capsid HIV Virus Virus Structure of a Virus • many are host specific – ex: bacteriophage only infects bacteria Structure of a Virus • contain. . . no cell organelles, • carry out. . . no metabolic reactions • reproduce. . . only inside a host cell Virus Virus Structure of a Virus • classified by type of nucleic acid and shape Virus Viral Reproduction Lytic Cycle (DNA virus) – virus takes over host cell, replicates, and destroys host cell • Steps – attachment – entry – replication – formation & assembly – lysis & release Virus Viral Reproduction Lytic Cycle (DNA virus) • viruses use nucleotides, ribosomes, tRNA, and amino acids of host cell • viruses that undergo the lytic cycle are called virulent – short incubation time rhino virus Viral Reproduction Lytic Cycle (DNA virus) Virus Virus Viral Reproduction Lysogenic Cycle (DNA virus) – virus invades cell and becomes part of its DNA for a time • Steps – attachment – entry – intergration • viral DNA breaks open host cell DNA and joins with it forming a provirus – cell division • host cell divides, produces 2 new host cells with the provirus inside Virus Viral Reproduction Lysogenic Cycle (DNA virus) • provirus may: – change phenotype of host – prevent other viruses from entering host – pull out of host DNA & enter lytic cycle Virus Viral Reproduction Lysogenic Cycle (DNA virus) • viruses that go through lysogenic cycle are temperate viruses – long incubation period herpes simplex Viral Reproduction Lysogenic Cycle (DNA virus) Virus Viral Reproduction Lysogenic Cycle (DNA virus) Virus Viral Reproduction RNA virus Lytic cycle Steps • (almost the same as DNA virus) – attachment – entry – replication • replication of viral RNA – formation & assembly – lysis & release Virus Virus Viral Reproduction RNA virus Lysogenic cycle Steps • inject viral RNA into host • viral RNA makes a DNA copy using reverse transcriptase • DNA strand replicates and enters host DNA to become a provirus Virus Viral Reproduction RNA virus Lysogenic cycle • RNA viruses that go through the lysogenic cycle are called retroviruses HIV Treating Viruses vaccine • injection of weakened or killed viruses Jonas Salk (1955) • developed first vaccine for the polio virus Virus Other Viruses polio Virus Other Viruses measles Virus Other Viruses smallpox Virus
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