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Exam 27: Protein Metabolism

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Question 21

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Following the synthesis of their polypeptide chain,many proteins require further posttranslational modifications before they attain their full biological activity or function.List and describe briefly at least four possible types of modification that can occur.

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(1)Amino-terminal modification (N-acetyl...

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Question 22

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A given mRNA sequence might be translated in any of three reading frames.Describe how prokaryotes and eukaryotes determine the correct reading frame.

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In prokaryotes,the Shine-Dalgarno sequen...

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Question 23

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Number the following steps in the proper order with regard to protein synthesis. ___ Aminoacyl-tRNA binds to the A site. ___ Deacylated tRNA is released from ribosome. ___ Peptide bond formation shifts the growing peptide from the P to the A site. ___ The 50S subunit binds to the initiation complex of the 30S subunit and mRNA.

The signal sequences that direct proteins to the nucleus are:

Which of the following statements about bacterial mRNA is true?

Which one of the following antibiotics does not function by interfering with the translational process?

Which of the following is true about the sorting pathway for proteins destined for incorporation into lysosomes or the plasma membrane of eukaryotic cells?

In E.coli,aminoacyl-tRNA synthetases:

You have isolated a fragment of viral DNA that totally encodes at least two proteins,120 and 80 amino acids long.The DNA fragment is 400 base pairs long. (a)Why might you consider this unusual? (b)You sequence the two proteins and find no sequence homology.Propose a model to account for these findings.

Consider the following hypothetical short mRNA;what would be the sequence of the protein produced if this were translated in an E.coli cell? 5'-AUAGGAGGUUUGACCUAUGCCUCGUUUAUAGCC-3'

Match the factor or enzyme at the right with the stage(s) of protein synthesis at which it acts. If a factor or enzyme participates in two stages of protein synthesis, indicate both of them.

Assuming that the average amino acid residue contributes 110 to the peptide molecular weight,what will be the minimum length of the mRNA encoding a protein of molecular weight 50,000?

Which one of the following is not true about RNA editing?

Which of the following is not one of the five steps of

Describe the role of ubiquitin in mediating intracellular protein breakdown.

In bacteria the elongation stage of

When first synthesized,proinsulin has an additional leader or signal peptide at its amino terminus.This complete molecule is called preproinsulin and the signal peptide is cleaved off to give proinsulin.Briefly,what is the likely function of the signal peptide?

The template strand of a segment of double-stranded DNA contains the sequence: (5')-CTT TGA TAA GGA TAG CCC TTC-(3') (a)What is the base sequence of the mRNA that can be transcribed from this strand? (b)What amino acid sequence could be coded by the mRNA base sequence in (a),using only the first reading frame starting at the 5' end? (c)Suppose the other (complementary)strand is used as a template for transcription.What is the amino acid sequence of the resulting peptide,again starting from the 5' end and using only the first reading frame?

Glycosylation of proteins inside the endoplasmic reticulum does not involve:

Indicate whether each of the following statements is true (T)or false (F). ___Assembly of a complete ribosome onto an mRNA requires ATP hydrolysis. ___Aminoacylation or "charging" of tRNA requires the formation of an aminoacyl-AMP intermediate. ___Aminoacyl-tRNA binding to the A site of the ribosome requires the accessory factor EF-G and GTP hydrolysis. ___Translocation of a growing polypeptide from the A to the P site on the ribosome requires EF-G and GTP hydrolysis. ___Termination of translation requires release factors,but no NTP hydrolysis.