ps7q_05

ps7q_05 - MIT Department of Biology 7.014 Introductory...

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MIT Department of Biology 7.014 Introductory Biology, Spring 2005 Name:______________________________________ Section :______ 7.014 Problem Set 7 A nswers to this problem set are to be turned in. Problem sets will not be accepted late. Solutions will be posted on the web. Question 1 Part A Shown below is a schematic representation of an antibody made in B cells. On the diagram label the following structures (a) – (d) on the antibody diagram. a) the antigen binding sites b) the heavy chains and the light chains c) the variable regions d) i) If this was a membrane-bound antibody, indicate the membrane-spanning region of the antibody ii) If this was a secreted antibody, indicate the region of the antibody that would interact with phagocytic cells e) List two ways that combinatorial joining generates antibody diversity.
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Question 1, continued Below is a schematic of the unrearranged immunoglobin heavy chain locus. V segments D segments J segments constant segment region a region b region c region d regions e a) Indicate which region(s) contribute(s) to the formation of the antigen binding site of the antibody molecule. b) After rearrangement, which region(s) would be the same in different B cells? c) Which region(s) would never appear in any mRNA transcribed from this locus in a population of mature B cells? d) Cindy wants to store cell samples from her chinchilla so that in the future she can produce a clone. She has isolated cell lines from the following four different cell types. However, freezer space in the lab is limited and she can keep only one. Which cell line should she keep? Red blood cell Gut cell B cell T cell Why keep this cell line rather than the others? 2
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Question 1, continued Part B The virus which causes AIDS (acquired immune deficiency syndrome) is called HIV (human immunodeficiency virus). HIV is a retrovirus, and its genome is a single RNA strand . Two copies of this RNA genome are packaged with two copies of the retroviral enzyme, reverse transcriptase, within a protein capsid. a) For HIV infection to occur, a surface protein on the virus must interact with a surface protein on the cell. HIV specifically infects the helper T cells of the human immune system. Give one explanation for how HIV infection is specific for helper T cells. b) Once infection has taken place, the RNA genome has to be made into double-stranded DNA. This process is mediated by reverse transcriptase. Once a double-stranded DNA copy of the HIV genome has been made, it is integrated into the host cell genome. The integration event is mediated by an enzyme, integrase. i) What are the three steps required to produce double-stranded DNA from the single strand
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ps7q_05 - MIT Department of Biology 7.014 Introductory...

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