3. In normal cells the amino acid phenylalanine attaches to tRNAs with the antic

Question

3. In normal cells the amino acid phenylalanine attaches to tRNAs with the anticodon AAA. The enzyme aminoacy!-tRNA synthetase catalyzes the reaction that attaches the amino acid to the correct tRNA. Assume that a mutation occurs in the aminoacyl-tRNA synthetase instead of phenylalanine to tRNAs with the anticodon AAA. What will be the consequence of this mutation for the translation process? enzyme and causes it to attach lysine Each of the following statements refer to processes that take place during translation. Indicate whether each statement is True or False. If the statement is false, explain how you could change the statement so that it would be true. a. During the initiation of translation, the codon AUG is found lined up with P site b. The start codon is the part of the mRNA that is used to ensure that the mRNA binds in the correct location on the small subunit of the ribosome. c. During the elongation phase of translation, tRNA's enter the ribosome through the E site. d. During the elongation phase of translation, the bond between the amino acid and tRNA in the P sites is broken, and a peptide bond is formed between this amino acid and the amino acid in A site.

Explanation / Answer

3.There is a process called as translational proofreading. This process ensures that no incorrect amino acid is incorporated in the polypeptide chain. Fersht and Keathner proposed that each aaRs has two sites : active site and editing site. If somehow active site through mutation or error attach an incorrect amino acid (say eg above case), the editing site removes this mismatched amino acid and replaces it with the normal amino acid. This proofreading constitutes the second genetic code. With the result fidelity of mRNA is ensured and maintained.

a. It is true that during initiation the initiation codon AUG binds with the P site of ribosome. It is the only codon which occupies the p site directly, all rest codons are exposed at A site.

b. This statement is false. It is not the start codon which ensures that the mRNA binds correctly with the ribosome but it is the UTR on the 5' end of mRNA which is complementary to the Shine Dalgarno sequence of ribosme that ensure mRNA binds correctly with the ribosome.

C. This statement is false. The correct statement is that during translation each new tRNA enters through A site of ribosme.

D. This statement is correct.

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