8. Which of the following point mutations would be most likely to affect protein
function?
a. TAA to TGA
b. CAA to TAA
c. AGG to AGA
d. CTT to CTC
Point Mutations Affecting Protein Function: CSIR NET Life Sciences Solved Question
CAA to TAA mutation creates a premature stop codon, drastically shortening the protein and most severely disrupting its function compared to other options.
Option Analysis
These DNA point mutations change single nucleotides in codons, with effects determined by the standard genetic code where TAA, TAG, and TGA signal translation termination.
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a. TAA to TGA: Both codons function as stop codons (ochre to opal), so translation terminates identically with no change in protein length or sequence.
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b. CAA to TAA: CAA codes for glutamine (Gln), but TAA introduces a premature nonsense stop codon, producing a truncated protein lacking essential C-terminal regions critical for folding and activity.
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c. AGG to AGA: Both code for arginine (Arg) in a synonymous (silent) change due to wobble degeneracy, preserving the amino acid sequence entirely.
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d. CTT to CTC: Both code for leucine (Leu) as another silent mutation with no amino acid substitution.
Correct Answer
Option b. CAA to TAA most likely affects protein function through nonsense-mediated truncation, a common mechanism in genetic diseases.
