AP-Bio-HW-18-091204 (1)

AP-Bio-HW-18-091204 (1) - Homework#18 Chapter 18(due Mon...

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Homework #18 : Chapter 18 (due Mon) ONE Concept Map: 10 points Objectives The Genetics of Viruses 1. Recount the history leading up to the discovery of viruses. Include the contributions of Adolf Mayer, Dimitri Ivanowsky, Martinus Beijerinck, and Wendell Stanley. In 1883 adolt Mayer was researching tobacco mosaic disease. He discovered the disease must be excedingly small for it to be transmitted by tree sap. In 1897, Martinus Beijerinck ruled out the possibility that the disease was due to a filterable toxin produced by a bacterium by demonstrating that the infectious agent could reproduce. In 1935, Wendell Stanley crystallized the pathogen, the tobacco mosaic virus (TMV). 2. List and describe the structural components of viruses. A virus is a genome enclosed in a protective coat. A virus is not a cell. They are infectious particles consisting of nucleic acid encased in a protein coat and, in some cases, a membranous envelope. 3. Explain why viruses are obligate intracellular parasites. Viruses are obligate intracellular parasites. They can reproduce only within a host cell. They insert their DNA into the host cell to create more virus. 4. Explain how a virus identifies its host cell. Viruses identify host cells by a “lock and key” fit between proteins on the outside of the virus and specific receptor molecules on the host’s surface (which evolved for functions that benefit the host). 5. Describe bacterial defenses against phages. 6. Distinguish between the lytic and lysogenic reproductive cycles, using phage lambda as an example. In the lytic cycle, the phage reproductive cycle culminates in the death of the host. In the lysogenic cycle, the phage genome replicates without destroying the host cell. Phage lamba can reproduce both ways. During a lytic cycle, the phage uses the cell to copy DNA releasing virus. During a lysogenic cycle, the viral DNA molecule is incorporated by genetic recombination into a specific site on the host cell’s chromosome. 7. Describe the reproductive cycle of an enveloped virus. Explain the reproductive
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cycle of the herpesvirus. The glycoproteins bind to the envelope. Capsid enter the cell and disolve releasing DNA, which is used as a template to make more DNA. New Virus bud from the cell, and capsid develope around viral genome. With herpes, the double-stranded DNA viruses reproduce within the cell nucleus using viral and cellular enzymes to replicate and transcribe their DNA. They stay in the nucleus until triggered to release. 8. Describe the reproductive cycle of retroviruses. These carry an enzyme called reverse transcriptase that transcribes DNA from an RNA template. The newly made DNA is inserted as a provirus into a chromosome in the animal cell. The host’s RNA polymerase transcribes the viral DNA into more RNA molecules. 9. List some characteristics that viruses share with living organisms and explain why
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AP-Bio-HW-18-091204 (1) - Homework#18 Chapter 18(due Mon...

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