19-3 Viruses Are they alive? Acellular Can not metabolize Can’t grow or respond to environment Can’t reproduce without host- obligate parasites Have DNA or RNA Evolve *can only be seen with electron microscope Yes No

Virion- virus outside of cell Capsid-protein coat surrounding nucleic acid Genetic material- DNA or RNA –dsDNA- double stranded DNA –ssDNA- single stranded DNA –dsRNA- double stranded RNA –ssRNA- single stranded RNA Super small amount of genes Capsomeres- Surface proteins- only attach to particular host or even specific cells in the host

Discovery- they were looking for the cause of Tobacco Mosaic Virus Adolf Mayer-disease is contagious Dmitri Ivanovsky- uses filter to trap “bacteria” 1897-Martinus Beijerinch- caused by something smaller than bacteria 1898-named virus- meaning “poison” Wendell Stanley- isolates virus

Bacteriophage Infects bacteria Replication- –2 cycles

Enveloped virion Membrane acquired from its host cell during viral replication or release Composed of phospholipid bilayer & proteins- specific for host attachment

Lytic Cycle (virulent-causes disease) 1.Attachment - the virus attaches itself to the host cell.Attachment 2.Injection - the virus inserts its genetic material into the host cell.Injection 3.Integration & Replication- the genetic material tells the cell what to do & the host cell builds parts of the virus.IntegrationReplication 4.Assembly - the cell assembles the replicated parts into new viruses.Assembly 5.Lysis - the cell breaks open and each replicated virus can now infect other cells.Lysis

Lysogenic Cycle (temperate- doesn’t kill right away) 1.Attachment 2.Injection 3.Integration- virus DNA becomes part of bacterial DNA- prophage 4.Replication- when host cell replicates its own DNA, virus DNA is also copied 5.Assembly 6.Trigger > Lytic Cycle can be caused by sunlight, radiation, chemicals

Lytic vs Lysogenic Cycles Uwww.youtube.com/watch?v=wVkCyU5aee U xKitsd0&feature=relatedhttp:// xKitsd0&feature=related

How do Animal viruses replicate? Same steps as bacteriophages, just some differences in what is happening in each –Ex: removal of outer coat

Latency -viruses remain dormant in cells Prolonged viral activity for years –Ex: chickenpox, herpes Can become integrated into host’s chromosomal information permanently, so all cells after that are infected –Ex: HIV

Viroids Small, circular pieces of RNA that are infectious to plants Lack capsids May appear linear

Prions Not viruses because they lack nucleic acid Composed of single protein- PrP –All mammals contain a gene that codes for the a.a. sequence for cellular PrP Can re-fold into stable structures, changing shape & become harmful Excess PrP or mutations cause the prion PrP 40% of humans have PrP that can misfold

Retroviruses Work “backwards” –RNA > DNA > RNA > Protein –HIV – O8whttp:// O8w

Treeman e-man-genetic-condition-growths-hands- legshttp:// e-man-genetic-condition-growths-hands- legs

Vaccines How are they made? –Reading – 068, _ ,00.htmlhttp://content.time.com/time/video/player/0,32 068, _ ,00.html