VIRUSES

The Genetics of Viruses  (L) poison  First identified by Stanley in Tobacco Mosaic Virus  A genome w/in a protective coat

Viral Structure  Capsid-protein coat that encloses the genome  Envelope-membrane that cloaks some capsids  Genome

Life Cycle  Obligate intracellular parasites  Range varies, depends upon receptor sites  Some with broad range-ex. Rabies  Some with very narrow range-ex. Human cold virus

Genome Replication  DNA  DNA uses host DNA polymerase  RNA  RNA virus has gene for RNA replicase  RNA  DNA  RNA usually virus contains gene for reverse transcriptase

Lytic Cycle  Virus uses cells enzymes, ribosomes, tRNAs, amino acids ATP, etc.  Viral particles self- assemble  Lytic cycle is fatal to cell  Called Virulent viruses

Lysogenic Cycle  Virus coexists within the host  Called temperate viruses  Viral genome is incorporated into the host’s genome  Called a Prophage

Animal Viruses

Reproductive cycles of Animal Viruses  Attachment-glycoprotein spikes attach to receptor sites  Entry-envelope fuses with plasma membrane, entire virus moves in via receptor mediated endocytsis  Uncoating- genome exposed  Viral RNA and protein synthesis  Assembly and release- virion “buds” through the surface, envelope is cells phospholipids with virus-specific glycoproteins

Influenza Animation  rces/HAAnimation.swf rces/HAAnimation.swf story.php?storyId= ttp:// story.php?storyId=

Emerging Viruses  Make a sudden appearance.  Not new, just a new territory  Examples: HIV, hantavirus, Ebola  Flu

Viruses and Cancer Some tumor viruses cause cancer in animals VIRAL GROUP  Retrovirus  Herpesvirus  Papovavirus  Hepatititis B virus CANCER TYPE  Leukemia  Burkitt’s lymphoma  Cervical cancer  Liver cancer

Plant Viruses  RNA viruses  Spread by horizontal transmission- from an external source  Vertical transmission-from parent

Viroids and Prions  Viroids are naked circular RNA  Probably disrupt metabolism, development, and growth  Plant pathogen  Prions are proteins  Cause degenerative brain diseases  “mad cow” disease  Creutzfeldt-Jakob disease  How? Hypothesis- misfolded and convert normal proteins to the prion version. Chain reaction.

Prion  “proteinaceous infectious particles”  Found in brains of all mammals  Products of gene expression  Some exist in a misfolded state, leads to ability to resist conventional sterilization  Infectious types are able to “latch” onto normal prions and convert them to that infectious type

How Prions reproduce

19.12 Prions Change Shape Slide number: 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Nucleus Cytoplasm Intracellular membrane Scrapie PrP All scrapie PrP Normal PrP Original scrapie PrP molecule Converted molecule Normal PrP

19.12 Prions Change Shape Slide number: 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Nucleus Cytoplasm

19.12 Prions Change Shape Slide number: 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Nucleus Cytoplasm Intracellular membrane Normal PrP Scrapie PrP

19.12 Prions Change Shape Slide number: 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Nucleus Cytoplasm Intracellular membrane Normal PrP Scrapie PrP

19.12 Prions Change Shape Slide number: 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Nucleus Cytoplasm Intracellular membrane Original scrapie PrP molecule Normal PrP Converted molecule Normal PrP Scrapie PrP

19.12 Prions Change Shape Slide number: 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Nucleus Cytoplasm Intracellular membrane Original scrapie PrP molecule Normal PrP Converted molecule Normal PrP Scrapie PrP

19.12 Prions Change Shape Slide number: 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Nucleus Cytoplasm Intracellular membrane Original scrapie PrP molecule All scrapie PrP Normal PrP Converted molecule Normal PrP Scrapie PrP

19.12 Prions Change Shape Slide number: 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Cytoplasm Nucleus

19.12 Prions Change Shape Slide number: 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Cytoplasm Nucleus Intracellular membrane Normal PrP Scrapie PrP

19.12 Prions Change Shape Slide number: 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Cytoplasm Nucleus Intracellular membrane Normal PrP Converted molecule

19.12 Prions Change Shape Slide number: 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Cytoplasm Nucleus Intracellular membrane

19.12 Prions Change Shape Slide number: 12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Cytoplasm Nucleus Intracellular membrane

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19.12 Prions Change Shape Slide number: 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Neuron Cytoplasm Nucleus Intracellular membrane

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19.12 Prions Change Shape Slide number: 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. All scrapie PrP Neuron Cytoplasm Nucleus Intracellular membrane

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