24. Use the following mRNA sequence to answer the questions that follow. end of

Question

24. Use the following mRNA sequence to answer the questions that follow. end of the exam. The genetic code is at the 5'-CCGUAAGAUGGAUCUCAAGAUGUACUGAAA -3 a. The above mRNA sequence is in the process of being translated by a ribosome. If the sequence of the anticodon for the tRNA in the P site is 5'-GAU-3',what amino acid is specified by the codon in the P site? b. What codon is in the A site at this time? c. Following peptide bond formation and translocation, what will be the next amino acid added to the growing peptide chain? d. Is there a stop codon in this reading frame? e. What happens when a stop codon is in the A site on the ribosome? f. What kind of mutation would result if the U in bold were substituted with an A in the defined reading frame?

Explanation / Answer

a. Aspartic acid

Aminoacid specified by the codon in the P site is Aspartic acid. If GAU become the anticodon for tRNA (CUA), tRNA brings Aspartic acid.

b. UCU

At this time at A site next triplet codon is present. Next triplet codon after GAU is UCU. So UCU is present at A site.

c. Serine

To the growing peptide chain next amino acid added is serine (for the codon UCU) and Glutamine (for the codon CAA). First amino acid is Aspartic acid then Serine and Glutamine.

d. No

For the same reading frame there is no stop codon in the forward direction. (Stop codon is present in the same reading frame behind GAU!. Stop codon there has the sequence UAA.

e. Translation terminates

If stop codon is there at A site, no tRNA binds to A site so translation terminates.

f. Glutamic acid added instead of Valine.

If due to mutation U is substituted by A, instead of Valine- Glutamic acid is added during translation. Because in the same reading frame GUA codes for Valine. If U is substituted by A, codon will be GAA. GAA codes for Glutamic acid.

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