Chapter 18 Viral Genetics Slide show modified from

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Chapter 18. Viral Genetics Slide show modified from: Explore. Biology by Kim Foglia 2005

Chapter 18. Viral Genetics Slide show modified from: Explore. Biology by Kim Foglia 2005 -2006

Hepatitis Viral diseases Polio Measles Chicken pox 2005 -2006

Hepatitis Viral diseases Polio Measles Chicken pox 2005 -2006

Influenza: 1918 epidemic 30 -40 million deaths world-wide RNA virus 2005 -2006

Influenza: 1918 epidemic 30 -40 million deaths world-wide RNA virus 2005 -2006

Smallpox § Eradicated in 1976 vaccinations ceased in 1980 u at risk population? u

Smallpox § Eradicated in 1976 vaccinations ceased in 1980 u at risk population? u 2005 -2006

Emerging viruses § Viruses that “jump” host switch species u Ebola, SARS, bird flu,

Emerging viruses § Viruses that “jump” host switch species u Ebola, SARS, bird flu, hantavirus u Ebola SARS hantavirus 2005 -2006

http: //www. biology. arizona. edu/cell_bio/tutorials/cells 2. html A sense of size § Comparing size

http: //www. biology. arizona. edu/cell_bio/tutorials/cells 2. html A sense of size § Comparing size eukaryotic cell u bacterium u virus u 2005 -2006

What is a virus? Is it alive? § DNA or RNA enclosed in a

What is a virus? Is it alive? § DNA or RNA enclosed in a protein coat § Viruses are not cells § Extremely tiny u u u electron microscope size smaller than ribosomes ~20– 50 nm 1 st discovered in plants (1800 s) § tobacco mosaic virus § couldn’t filter out § couldn’t reproduce on media like bacteria 2005 -2006

Variation in viruses plant virus § Parasites u u u pink eye lack enzymes

Variation in viruses plant virus § Parasites u u u pink eye lack enzymes for metabolism lack ribosomes for protein synthesis need host “machinery” 2005 -2006

Variation in viruses § A package of influenza bacteriophage genes in transit from one

Variation in viruses § A package of influenza bacteriophage genes in transit from one host cell to another “A piece of bad news wrapped in protein” – Peter Medawar 2005 -2006

Viral genomes § Viral nucleic acids u DNA § double-stranded § single-stranded u RNA

Viral genomes § Viral nucleic acids u DNA § double-stranded § single-stranded u RNA § double-stranded § single-stranded u Linear or circular § smallest viruses have only 4 genes, while largest have several hundred 2005 -2006

Viral protein coat § Capsid crystal-like protein shell u 1 -2 types of proteins

Viral protein coat § Capsid crystal-like protein shell u 1 -2 types of proteins u many copies of same protein u 2005 -2006

Viral envelope § Lipid bilayer membranes cloaking viral capsid u envelopes are derived from

Viral envelope § Lipid bilayer membranes cloaking viral capsid u envelopes are derived from host cell membrane § glycoproteins on surface HIV 2005 -2006

Generalized viral lifecycle § Entry u virus DNA/RNA enters host cell § Assimilation u

Generalized viral lifecycle § Entry u virus DNA/RNA enters host cell § Assimilation u u viral DNA/RNA takes over host reprograms host cell to copy viral nucleic acid & build viral proteins § Self assembly u u nucleic acid molecules & capsomeres then selfassemble into viral particles exit cell 2005 -2006

Symptoms of viral infection § Link between infection & symptoms varies kills cells by

Symptoms of viral infection § Link between infection & symptoms varies kills cells by lysis u cause infected cell to produce toxins u § fever, aches, bleeding… u viral components may be toxic § envelope proteins § Damage? u depends… § lung epithelium after the flu is repaired § nerve cell damage from polio is permanent 2005 -2006

Viral hosts § Host range u most types of virus can infect & parasitize

Viral hosts § Host range u most types of virus can infect & parasitize only a limited range of host cells § identify host cells via “lock & key” fit § between proteins on viral coat & receptors on host cell surface u broad host range § rabies = can infect all mammals u narrow host range § human cold virus = only cells lining upper respiratory tract of humans § HIV = binds only to specific white blood cells 2005 -2006

Bacteriophages § Viruses that infect bacteria § ex. phages that infect E. coli §

Bacteriophages § Viruses that infect bacteria § ex. phages that infect E. coli § lambda phage 20 -sided capsid head encloses DNA u protein tail attaches phage to host & injects phage DNA inside u 2005 -2006

Bacteriophage lifecycles § Lytic reproduce virus in bacteria u release virus by rupturing bacterial

Bacteriophage lifecycles § Lytic reproduce virus in bacteria u release virus by rupturing bacterial host u § Lysogenic integrate viral DNA into bacterial DNA u reproduce with bacteria u 2005 -2006

Lytic lifecycle of phages 2005 -2006

Lytic lifecycle of phages 2005 -2006

Lysogenic lifecycle of phages 2005 -2006

Lysogenic lifecycle of phages 2005 -2006

Defense against viruses § Bacteria have defenses against phages u bacterial mutants with receptors

Defense against viruses § Bacteria have defenses against phages u bacterial mutants with receptors that are no longer recognized by a phage § natural selection favors these mutants u bacteria produce restriction enzymes § recognize & cut up foreign DNA § It’s an escalating war! u natural selection favors phage mutants resistant to bacterial defenses 2005 -2006

RNA viruses § Retroviruses u have to copy viral RNA into host DNA §

RNA viruses § Retroviruses u have to copy viral RNA into host DNA § enzyme = reverse transcriptase § RNA DNA m. RNA u host’s RNA polymerase now transcribes viral DNA into viral m. RNA § m. RNA codes for viral components § host’s ribosomes produce new viral proteins transcription DNA replication translation RNA protein 2005 -2006

Retroviruses § HIV u u Human Immuno. Deficiency Virus causes AIDS § Acquired Immuno.

Retroviruses § HIV u u Human Immuno. Deficiency Virus causes AIDS § Acquired Immuno. Deficiency Syndrome § opportunistic diseases u u envelope with glycoproteins for binding to specific WBC capsid containing 2 RNA strands & 2 copies of reverse transcriptase 2005 -2006

HIV infection § HIV enters host cell u macrophage & CD 4 WBCs §

HIV infection § HIV enters host cell u macrophage & CD 4 WBCs § cell-surface receptor u reverse transcriptase synthesizes double stranded DNA from viral RNA § Transcription produces more copies of viral RNA u u u translated into viral proteins & v. RNA self-assemble into virus particles released from cell by “budding” or by lysis 2005 -2006

Cancer viruses § Viruses appear to cause certain human cancers u hepatitis B virus

Cancer viruses § Viruses appear to cause certain human cancers u hepatitis B virus § linked to liver cancer u Epstein-Barr virus = infectious mono § linked to lymphoma u papilloma viruses § linked with cervical cancers u HTLV-1 retrovirus § linked to adult leukemia 2005 -2006

Cancer viruses § Transform cells into cancer cells after integration of viral DNA into

Cancer viruses § Transform cells into cancer cells after integration of viral DNA into host DNA carry oncogenes that trigger cancerous characteristics in cells u version of human gene that normally controls cell cycle or cell growth u § Most tumor viruses probably cause cancer only in combination with other mutagenic events 2005 -2006

Prions § Misfolded proteins infectious u make plaques (clumps) & holes in brain as

Prions § Misfolded proteins infectious u make plaques (clumps) & holes in brain as neurons die u Creutzfeldt-Jakob disease “mad cow” disease 2005 -2006

1982 | 1997 Protein as information molecule? ! § Prions challenge Central Dogma u

1982 | 1997 Protein as information molecule? ! § Prions challenge Central Dogma u transmit information to other proteins Pn Stanley Prusiner Pd UC School of Medicine proteinaceous infectious 2005 -2006 molecule