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NEETZoologyMolecular Basis of Inheritance

Consider the following short mRNA sequence: 5'-AUG-UUU-UCA-UAG-3' If a point mutation occurs such that the sixth nitrogenous base from the 5' end is changed from Uracil (U) to Cytosine (C), what will be the effect of this mutation on the synthesized polypeptide?

Options

  1. AThe synthesis of the polypeptide will stop prematurely after the first amino acid.
  2. BThe second amino acid in the polypeptide chain will be replaced by Leucine.
  3. CThe amino acid sequence of the polypeptide chain will remain unchanged.
  4. DThe reading frame will shift, altering all subsequent amino acids.

Correct answer

C. The amino acid sequence of the polypeptide chain will remain unchanged.

Step-by-step solution

The given mRNA sequence is 5'-AUG-UUU-UCA-UAG-3'. The codons are read as AUG, UUU, UCA, and UAG. The 6th base from the 5' end is the third base of the second codon (UUU). A point mutation changing this Uracil (U) to Cytosine (C) alters the second codon from UUU to UUC. According to the genetic code, both UUU and UUC code for the same amino acid, Phenylalanine. This is due to the degeneracy of the genetic code, where some amino acids are coded by more than one codon. Therefore, the mutation will not change the amino

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