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MT1_09_key - Bio 115 Winter 2009 Midterm#1 January 27 Name...

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Bio 115, Winter 2009 Name__________________ Midterm #1, January 27 _____________________________________________________________________________________________________________________________ _ page 1 page total: Instructions: Write your name in ink at the top of every page. Do not write on the back of pages. Restrict your answers to the space provided. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Answer the following questions with "true" or "false". For each "true" answer, give a brief example or explanation that supports the statement. For each "false" answer, briefly explain why the statement is false. (3 points each) 1. Human genes on average are much larger than E. coli genes because they encode for bigger proteins. False. Human genes are larger because they contain introns. 2. A cDNA library will reflect the transcription level of genes in the cells from which it was derived. True. cDNA is derived from mRNA, so more highly expressed genes have a higher probability of being found in the library. 3. Across species, centromeric DNA can be identified by its high sequence conservation. False. Although centromere function is highly conserved, centromeric DNA sequence is highly divergent 4. In order to amplify a region of DNA by PCR, it is not necessary to know the sequence of that entire region. True. One must only know the sequence at the ends of the region for designing complementary primers. 5. A northern blot cannot be used to identify an unknown gene transcript. True. In order for the northern probe to bind to the target RNA, it must contain a complementary sequence. Thus the target sequence must be known. 6. Purified RNA polymerase II does not bind the core promoter efficiently. True. RNA pol II requires general transcription factors (especially TFIID) to bind the core promoter.
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Bio 115, Winter 2009 Name__________________ Midterm #1, January 27 _____________________________________________________________________________________________________________________________ _ page 2 page total: +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Short answer questions. Limit your answer to the space provided. (4 points each) 7. The general transcription factors (GTFs) for RNA polymerases I and III form much more stable complexes with promoters than the general factors for RNA polymerase II. Provide a hypothesis explaining this observation. The relatively few Pol I and III genes are typically always highly transcribed and require the GTFs presence constantly. The many different genes Pol II genes are regulated in many different ways and must respond quickly to changing environmental signals etc meaning that the GTFs must be able to rapidly go on and come off of promoters. 8. Which feature(s) of the human genome is the primary reason that it is so much larger than the genomes of prokaryotes. What is the proposed function of the feature(s)? Repetitive DNA sequences comprise nearly half of the human genome. These are mainly derived from selfish genetic elements that have no obvious function to the host. (will also accept a discussion of introns and their role in generating diverse proteins from a limited number of genes) 9. Choose two of the Pol II general transcription factors and give a one-sentence description of each of their roles in transcription.
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