HW #18 - AP Biology Period 4 #22 Liem Nguyen 11/21/09...

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AP Biology Period – 4 #22 Liem Nguyen 11/21/09 Homework #18 (091204): Chapter 18 (due Friday 091204 ) Total points: 20 for Attempt on all questions 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. Adolf Mayer: rubbing extracted sap from diseased leaves onto healthy plants can spread diseases, bacteria are microscopic Dimitri Ivanowski: sap from infected tobacco leaves through filter, other leaf still infected, filter made toxin passed onto the leaf Martinus Beijerinck: infectious agent in sap can reproduce, pathogen reproduced only in host, infected by something smaller and simpler than bacteria Wendell Stanley: saw viruses through electron microscope It was thought at first that bacteria were microscopic. It was confirmed that bacteria were microscopic, but since the agent of the disease could reproduce, it had to be much smaller than bacteria. This was confirmed when the virus was seen on the electron microscope. 2. List and describe the structural components of viruses. smaller than ribosome A virus is an infectious agent that is smaller than a ribosome. It has a protein coat, or a membranous envelope, to protect the nucleic acids inside. 3. Explain why viruses are obligate intracellular parasites. reproduce in host cell only no metabolic enzymes, ribosomes, other components for making proteins they only have genes Viruses are obligate intracellular parasites because the only way they can reproduce is within the host cell or to infect another. This is because viruses lack metabolic enzymes, ribosomes, and many other organelles required for making proteins. This way, they only contain the genes to transmit diseases. 4. Explain how a virus identifies its host cell. host range: limited range of host cells “lock-and-key” Virus can identify the host cell by trying to fit between the proteins on the outside of the virus and the specific receptor molecules on the surface of the cells. However, this only
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works in a virus’s host range, which can be as big or as small as it can get. 5. Describe bacterial defenses against phages. natural selection foreign Lysogenic cycle restriction enzyme: cut up foreign material in cell Natural selection favors mutant bacteria with receptors that aren’t recognized my phages. Also, when DNA enters the bacterium, it is foreign material and cut up by the restriction enzymes. Finally, most phages coexist with the host cell during the lysogenic cycle. 6. Distinguish between the lytic and lysogenic reproductive cycles, using phage lambda as an example. Lytic cycle: phage reproductive cycle results in the death of host cell Lysogenic cycle: replicates phage genome without destroying the host Temperate phage: phages capable of using both modes of reproduction The lytic cycle causes cells to lyse while the lysogenic cycle does not. The lambda phage is a temperate phage. It forms while inside the host. During the lytic cycle, there is a mass
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HW #18 - AP Biology Period 4 #22 Liem Nguyen 11/21/09...

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