Gen511Exam1-07Key

Gen511Exam1-07Key - 1 Name GDCB 511 Exam I 100 Points 1...

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Name: GDCB 511 Exam I, 1-29-07 100 Points 1. Answer 5 of the 6 questions in section a-f below (12 points each, 60 points total) a. What are the functions of σ factor in the prokaryotic RNA polymerase complex and how does it perform these functions? (4 points each) -recognizes promoters by binding -35 box and -10 box of the core promoter; -recruits core RNA polymerase to the promoter, by interacting with core enzyme; -melts DNA in promoters to initiate transcription; three aromatic residues from σ are implicated in melting the DNA by substituting for basepairs. b. What’s the function of α subunit in the prokaryotic RNA polymerase complex? List two mechanisms by which α subunit performs its function. Activate transcription by recruiting RNA polymerase to the promoter (4 points) through two mechanisms: -binding to UP elements (4 points) or -interacting with other proteins such as CAP-cAMP (that binds to the CAP binding site) (4 points) 1
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c. If you grow E. coli in medium that contains both glucose and lactose, what the growth curve will you get? Draw the growth curve and indicate the expression status of the β -galactosidase (LacZ) gene at each phase. Figure 7.1; three phases Phase one: glucose used; lacZ off (4 points) Phase two: glucosed is used up; making lacZ (on) (4 points) Phase three: lactose is used, LacZ on (4 points) d. Tryptophan biosynthesis is controlled by both TrpR repressor and attenuation mechanisms. (1) How does the tryptophan level regulate transcription termination by the attenuation mechanism? (2) What would happen if the trp codons
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Gen511Exam1-07Key - 1 Name GDCB 511 Exam I 100 Points 1...

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