PS_6_older_key - Bio 115, Winter 2005 Problem set #6...

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February 18, 2005 Problem set #6 - 1 - 1. You have prepared an antibody that recognizes the 5' cap of human mRNAs with a high affinity. You prepare a cell lysate and perform an immunoprecipitation. What sorts of molecules are likely to be present in the immunoprecipitate? Answer : Remember that mRNA is associated with many proteins. So, we should see, mRNA hnRNP proteins RNA polymerase (remember, capping is a cotranscriptional event) poly-A-binding proteins snRNPs ribosomes translation factors 2. How is the 5' cap important for mRNA stability? For translation? Answer : It protects mRNAs from degradation, and is bound by translation initiation factor eIF4f. 3. Where in the cell does capping of mRNAs occur? Answer In the nucleus, very early in the process of transcription. 4. What protein(s) binds the 3' end of mRNAs? Answer Poly-A binding proteins 5. Besides alternative splicing, how can a mRNA be used to generate multiple different proteins? Answer By 'recoding', use of selenocysteine tRNAs and ribosomal frameshifting. 6. What are some of the major differences between translation in prokaryotes and eukaryotes? Answer Eukaryotes identify the site of initiation via scanning. Eukaryotic RNAs are usually monocistronic. Eukaryotes use a cap dependent mechanism of translation. (see pg 226 of the reader for other differences) 7. What are some of the energy dependent steps in translation? Answer
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PS_6_older_key - Bio 115, Winter 2005 Problem set #6...

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