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Biochemistry

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Purines, Pyrimidines and Nucleic Acid Metabolism

Question
46 out of 59
 

The End Codon of t-RNA at poly (A) “tail” codes for?(AIIMS May 2011)



A Poly alanine
B Poly proline

C Poly lysine
D Poly glycine

Ans. C Poly lysine

a. Poly (A) tails are added to the 3′end of mRNA molecules in a posttranscriptional processing step. The mRNA is first cleaved about 20 nucleotides downstream from an AAUAA recognition sequence.

b. Another enzyme, poly(A) polymerase, adds a poly(A) tail which is subsequentlyextended to as many as 200 A residues.

c. The poly(A) tail appears to protect the 3’-end of mRNA from 3’5’exonuclease attack. The presence or absence of the poly (A) tail does not determine whether a precursor molecule in the nucleus appears in the cytoplasm, because all poly(A)-tailed hnRNA molecules do not contribute to cytoplasmic mRNA, nor do all cytoplasmic mRNA molecules contain poly(A) tails.

Purines, Pyrimidines and Nucleic Acid Metabolism Flashcard List

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