[2]Viruses and Prokaryotes

[2]Viruses and Prokaryotes - Vi ruses and Prokaryotes...

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Unformatted text preview: Vi ruses and Prokaryotes (Chapter 24) What is the structure of a virus? Contrast a virus with a living cell Virus 1. Why do we call viruss a-cellular? Can they be viewed by the light microscope-if not why not? A-cellular: cannot independently performed metabolic activities (outside host) Sub cellular particle: small enough to pass through filter that block prokaryotes Poliovirus 30nm diameter Smallpox 300nm diameter Mimivirus 400nm diameter 2. Do viruses contain both DNA and RNA? Describe the four main virus structures? Why do some viruses have spikes in their outer capsids? (fig. 24-1) RNA or DNA genome Surrounded by protein coat(capsid) Contain either RNA or DNA not both ssDNA, dsDNA, ssRNA, dsRNA contain nucleic acids necessary to make copies of themselves but must invade and use metabolic machinery of living cells in order to produce Viruss tales over metabolic machinery of the cell; after invading hosts. Hosts synthesize capsid (protective protein coat) Virus structure T MV (tobacco mosaic virus) Helical Adenovirus (e.g. respiratory infection) T4 (infects E. Coli), bacteriofage Enveloped viruses A virus is a small particle What about its evolution 3. A virus is a small particle consisting of a nucleic acid genome surrounded by a protein coat, and may be enveloped. Explain the Escaped Gene Hypothesis, ad how does this explain the evolution of viruses? The escaped gene hypothesis Viruses may be bit s of nucleic acid that originally escaped from animal plant to bacterial cells (the three domains) as mobile genetic elements: o Transposons A DNA sergent that can move from one chromosome to another, or to distant sites within the same chromosome o Plasmids Small circular dsDNA molecules that carry genes distinct from those in the main DNA of a cell o Fragment moved from cell to cell Viruses may have evolved earlier before three domain emerges Mimiviruses have the genes that encode some of the components for protein translation o Evolved form a more complex ancestor; gradually lost some o the genes necessary for protein synthesis o Became dependent upon a host doe complete protein synthesis 4. Viruses have lytic and lysogenic reproductive cycles. Differentiate between each. Does a temperate virus have a lytic or a lysogenic cycle? Which one favors evolution of viruses?(Fig. 24-2, 24-3) What is the importance of lysogenic conversion to the properties of bacteria and their pathology? Give a couple of examples. 5. Briefly describe the 10 main steps involved in the lytic cycle of a membrane virus; Why are the host cell receptors important for viral entry; if the host cell machinery were unavailable to the virus would it be able to replicate; why or why not?...
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[2]Viruses and Prokaryotes - Vi ruses and Prokaryotes...

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