Chem_142C-08%20midterm2_KEY

Chem_142C-08%20midterm2_KEY - Name:_KEY_Perm #_ Chem...

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Name:__ KEY ________________________Perm #__________ Chem 142C/242C May 15, 2008 Midterm #2 Problem Points/Possible 1 / 1 0 2 / 1 0 3 / 1 2 4 / 6 5 / 5 6 / 1 5 7 / 1 4 8 / 1 2 9 /8 10 /20 11 /10 12 /28 _______________ TOTAL /150 Please be aware that some questions give more points than others.
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1) Explain with a schematic the general pathway of replicative transposition. (10 pnts) 2) How does rho-dependent transcription termination differ from rho-independent termination in prokaryotes? (10 pnts) In both, the transcription complex pauses at specific sequences in the DNA template. In ρ -independent termination, the formation of hairpin structures causes pausing which leads to dissociation of the product RNA and the polymerase from the template DNA and hence to termination. In ρ - dependent termination, the features that cause pausing are unclear, and dissociation requires the presence of the ρ protein.
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3) For each of the following statements, indicate with a P if the statement applies only to prokaryotes, an E if the statement applies only to eukaryotes, and an E & P if the statement applies to both eukaryotes and prokaryotes. (12 pts) _ __ RNA synthesis is blocked by actinomycin D. __ P _ A single RNA polymerase transcribes genes that encode mRNAs, tRNAs, and rRNA. __ E _ Transcription of mRNA is blocked by α -amanitin. _ P __ Sigma ( σ ) subunit detaches from RNA polymerase shortly after transcription has initiated. _ P __ The 5 ' end of the mature mRNA begins with a triphosphate. __ E _ The primary mRNA transcript is inacitve. 4) Below, an RNA molecule is being transcribed from a strand of DNA. Indicate the 5 ' and 3 ' ends of the RNA molecule and of the strand of DNA that is complementary to the RNA molecule. In which direction is synthesis occurring? (6 pts) 5) The specific sequences that E. coli RNA polymerase usually binds to in E. coli DNA before initiating transcription generally contain more A=T base pairs than G C base pairs. Why this might be the case? (5pts) Because A=T base pairs are stabilized by only two hydrogen bonds (compared with three for G±C pairs), double-stranded regions rich in A=T pairs are easier for RNA polymerase to bind and unwind in preparation for the transcription of one of the DNA strands.
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6) What do you find on the 3’ and 5’ ends of eukaryotic mRNA after processing?(3 pts) Draw the chemical structure of the 5’end of an eukaryotic mRNA after it has been processed. (12 pts) At the 5 ' end there is a cap consisting of a guanosine joined to the 5 - terminal nucleotide through a 5 to 5 triphosphate group. This guanine nucleotide is methylated on N-7. The next two nucleotides in the chain are also sometimes methylated on their 2
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This note was uploaded on 07/13/2009 for the course CHEM 142c taught by Professor Reich,n during the Spring '08 term at UCSB.

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Chem_142C-08%20midterm2_KEY - Name:_KEY_Perm #_ Chem...

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