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GDCB 511Exam 3_4-10-09 with key (1)

GDCB 511Exam 3_4-10-09 with key (1) - GDCB 511 Exam 3 10...

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GDCB 511, Exam 3: 10 April 2009 Name: 1. Short answer; answer any five. (4 points each; total 20) a. What 3 enzymatic activities are required for RNA capping? 1) RNA triphosphatase to remove gamma phosphate from the 5’ end RNA; 2) Guanylyltransferase to add the GMP part of GTP to form a triphosphate linkage; 3) methyltransferase to add a methyl group from AdoMet to the 2’ hydroxyl group of the penultimate nucleotide. b. What are the functions of Poly(A)? What is the sequence for the first stage of polyadenylation? 1) Poly(A) functions for RNA stability and translatability; also for splicing of first intron and transport of mRNA out of the nucleus. 2) Poly A signal AAUAAA at 3’ end of pre-mRNA is required for addition of the first portion of poly A tail c. Give a specific reason why single strand DNA cannot undergo the “lariat” mechanism of splicing. During nuclear mRNA precursor splicing process, the 2’-hydroxyl group of an adenosine nucleotide within the branchpoint of the intron attacks the phosphodiester bond linking the upstream exon to the intron to form the “lariat” RNA fragment. While in ssDNA, the nucleotide does not have the 2’-hydroxyl group which is the essential for forming a “lariat”. d. Give one piece of evidence that CPSF can bind to the polyA signal in mRNA. Gel mobility shift assay shows that CPSF can bind to RNA containing AAUAAA, but not to RNA containing AAGAAA (Weaver Figure 15.22). e. What is a Shine-Dalgarno sequence and what is its function? AGGAGGU consensus sequence at the ribosome-binding site in prokaryotic mRNA (or upstream of the initiation codon) which complementary to the very 3’ end sequence of the 16S rRNA. rRNA binding; initiation of mRNA translation; f. Describe the evidence that RNAi can induce methylation of gene promoter sequences? Silencing RNA targeted to promoter sequences results in promoter methylation, which can be detected as inability to be cut by a methylation-sensitive restriction enzyme. This causes a difference in the ability to PCR the promoter sequence (if methylated, DNA does not cut, and therefore can be amplified by PCR; if not methylated, DNA does cut and therefore can’t be amplified by PCR using flanking primers.).
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