Study Guide 4 - UNIT 4 STUDY GUIDE(MODIFIED(MICR 3050 FALL...

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UNIT 4 STUDY GUIDE (MODIFIED) (MICR 3050, FALL 2014) OBJECTIVES: Chapter 6.1 – 6.5 1. Compare and contrast bacterial and animal viruses. a. bacterial viruses ( bacteriophages ) i. enter cell by injection of nucleic acid 1. replicate after entering the genome ii. usually double stranded DNA iii. usually unenveloped b. animal viruses i. usually have an envelope ii. whole virion enters via fusion/phagocytosis/endocytosis iii. exit through budding 2. Describe bacteriophages. a. 1/3 of bacterial mortality is caused by viruses b. usually inject their DNA c. most bacteriophages have no envelope d. most are naked dsDNA e. 70% of marine prokaryotes are infected with a virus 3. Distinguish between virulent (lytic) and temperate (lysogenic) bacteriophages and their life cycles using T4 phage and lambda phage as examples, respectively. a. lytic cycle (T4) – only capable of the lytic cycle i. begins multiplying immediately after entering the host ii. lyses bacterial host cell for release of virions 1. 100 viruses released when cell lyses – burst size iii. steps: 1. attachment ( adsorption ) to the host cell surface 2. DNA is injected into the cell 3. early mRNA made 4. host DNA degraded by nucleases 5. viral DNA replicated 6. late mRNA made – structural role 7. self- assembly = package head first, then tail 8. heads filled 9. virions formed 10. host cell lysis b. lysogenic (temperate) phages – ex. lambda (infects E. coli) i. can either enter as lytic phages OR remain within host cell without destroying it 1. integrate genome into host genome in a relationship called lysogeny 2. lysogenic will eventually become lytic 3. can be advantageous to both virus and bacteria 4. integrated virus – prophage pops out of chromosome in induction & starts making mRNA
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4. Explain lysogeny and how the lytic cycle may be induced in lysogens. a. lysogeny – nonlytic relationship between a phage and its host i. virus uses integrase enzyme to integrate into host chromosome 1. lac operon - always integrates between galactose and biotin operons attachment site 2. replicates with host genome b. prophage – integrated bacteriophage genome i. form of the virus that remains within its host c. lysogens – infected bacterial host (contains prophage) i. appears normal ii. prophage may change the phenotype of its host – lysogenic conversion iii. 2 distinguishing factors: 1. immunity to superinfection – can’t be reinfected by the same virus 2. phage may switch form lysogenic cycle to lytic cycle upon induction a. when conditions within the cell cause the prophage to initiate synthesis of phage proteins and to assemble new virions b. commonly caused by changes in growth conditions or UV irradiation of the host cell – drops in levels of lamda repressor d. excionase – binds integrase enzyme i. enables integrase to reverse integration process under stress 5. Describe the effects of animal viruses on their hosts.
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  • Spring '13
  • Whitehead
  • DNA, i., Ebola virus

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