Lecture 201)Describe the different structures adopted by viruses a) DNA or RNASingle or double strandedb) One or several segmentsc) Circular or linear2)Describe the major molecular and structural components of viruses a) Molecularb) Structurali) Typically highly symmetricii) Filamentous or icosahedraliii) Many are more complex (head and tail)3)Explain why viruses are obligate parasites a) They can only reproduce with in host cells because they lack metabolicenzymes, ribosomes, and other equipment for making protiens4)Describe the origin and composition of virus envelopes a) Mostly found in animals a few in bacteria as wellb) Nucleocapsid is surrounded by a lipid bilayer and associated proteinsc) Membrane originates from he host cell by buddingd) Envelope proteins can be from the host cell or virus encoded5)Describe the function of viral envelope proteins a) Recognition of and attachment to specific host cellsb) Viral release from infected host cells6)Describe what bacteriophages are a) A virus infecting bacteriab) Common sturctures inclide icosahedral filamentous and head and taili) Because of the small capsid internal volume the genome must be very smallii) Efficient use of genetic materialiii) Many phages genomes have overlapping genes: same region of DNA encodes 2 or 3 proteins using different reading frames7)Describe the two main states of viruses a) Virulent- only reproduces y a lytic cycle b) Lysogenic- type of phage reproductive cycle in which the viral genome becomes incorporated into the bacterial host chromosomes as a prophage and does not kill the host 8)Describe what the genomes of viruses are made of a) DNA or RNA i) DNA: DS chicken poxii) RNA: HIV influenza b) Single or doubles strandedc) One or several segmentsd) Circular or linear9)Explain how viruses can have very small genomes a) They have overlapping genes same region of DNA codes for 2 or 3genes10)Explain what lysis is, and how it can be observed in a bacterial culture a) Culture becomes clear, seen with all lytic virusesb) Lysis- rupture of cell membrane and release of viruses and shit 11)Explain how you would proceed to measure virus titer a) You measure the titer by the number of PFU and that is titer of the phage suspension12)Explain what PFU means a) Plaque forming unitsi) Titer of the phage suspension13)Explain what a plaque is a) Visible structure within a cell culture such a bacteria and when bacteriophages replicate and spread they generate regions of cell destructions known as plaques b) Zone where cells have lysed and appears as a clear area in the lawn of host cells. Each plaque originates from a single infected cell14)Explain what a permissive host is a) The cell that allows the virus to infectb) A virus surface protein recognizes a specific receptor on the host cell surface: host specificity15)Explain what the latent period is during a lytic phage replication cycle a) Virus is present but does not replicate 16)Describe the successive steps in the replication cycle of T4 bacteriophage a) Expression of different genes is timed so the correct viral components are available at the right time to assemble the virusb) Early proteins modify the host RNA polymerase so it recognizes viral promotors only (anti sigma factors) 17)Explain how the T4 bacteriophage diverts the host gene expression machineryto its own advantage a) RNA polymerase + sigma factor (helps recognize promoter) one of the early proteins is an anti sigma factor block host sigma factor will block transcription of host genes 18)Explain how the T4 phage controls expression of its early, middle, and late proteins a) Expression of different genes is times so the correct viral components are available at the right time to assemble the virus19)Compare and contrast the life cycles of lytic and lysogenic phages a) Lytici) Virus replicates and lyses the host cellb) Lysogenic pathwayi) Virus DNA incorporates into the host genome20)Describe the two possible life cycles of phage λ a) Lyticb) Lysogenicc) LOOK AT SLIDE FIGURE21)Explain the mechanism that controls which pathway, lytic or lysogenic, istaken by phage λ a) Depends on the repressors if Cro> cI it goes lytic if CI>Cro then it goes lysogenic22)Explain what prophage induction is a) The prophage can excise form the genome under stress23)List the four possible outcomes of an animal viral infectiona) Transformation i) Some viruses can convert a normal host cell into a tumor cellb) Virulent Infectioni) Most common outcome, result in cell lysisc) Persistent infectioni) Slow release of viruses by budding, often does not kill the celld) Latent infection i) Virus present but does not replicate (analogous to a bacterial lysogen)24)Compare and contrast latent and persistent infectionsa) Latenti) Virus present but does not replicate (analogous to a bacterial lysogen)b) Persistent i) Slow release of viruses by budding, often does not kill the cell25)Name a virus causing persistent infections a) HIV26)Describe the composition of retrovirus genomes a) An enveloped single stranded RNA virus with a dsDNA intermediateb) Surface envelope proteinc) Lipid bilayerd) Core shell proteine) Transmembrane envelope proteinf) Capsid proteing) RNAh) Enzymesi) Reverse transciptaseii) Integraseiii) protease27)Describe the overall structure of the HIV-1 retrovirusa)28)Name the enzyme unique to retroviruses a) Reverse transciptasei) Convert sRNA to DNA29)Describe the different steps in a retrovirus life cycle a) Entry of the retrovirus into host cell, release of the nucleocapdis and release of the RNA genomeb) Reverse transcriptase converts RNA to DNAc) Viral DNA enters nucleus and integrates into genome, resulting in a privirusd) Transcription of the proviral30)Describe how reverse transcriptase and protease are involved in retrovirus replication a) Reverse transcriptase converts RNA to DNAb) Some proteins produced as pre-proteins are cleaved by protease31)Explain how HIV causes persistent infections a) when HIV inserts into cancer genes, the human cells proliferate more than when HIV is inserted into other genes. The proliferating cells form clones of infected
View Full Document
Unlocking...