A gene has undergone mutation in that one DNA base is substituted by another DNA

Question

A gene has undergone mutation in that one DNA base is substituted by another DNA base. Which of the following is UNLIKELY when comparing the protein made from the mutant gene to the protein made from the normal gene? The protein made from the mutant gene contains the same number of amino acids but one of the amino acid is different. O O The protein made from the mutant gene is much shorter than the normal protein. O This mutation results in no change to the protein product made from the mutant gene. O The protein made from the mutant gene has the same number of amino acids but several of the amino acids are different.

Explanation / Answer

Ans. Correct option- D. Change in peptide sequence by several amino acids while not affecting the length of peptide occurs due to frameshift mutation – the mutation in which one or more nucleotides (the number of nucleotides in not equal to or multiple of 3) is inserted or deleted from DNA molecule. A substation is replacement of one nucleotide with the other. Since substitution mutation does not change the reading frame, the change in peptide sequence is limited to one amino acid per mutation. So, it is UNLIKELY that a substitution mutation changes the amino acid sequence in bulk.

# Option A- likely to occur: The point mutation that changes amino acid sequence is called a Missense Mutation. Silent point mutation arise due to substitution of one base with another base AND the mutated codon encodes a different amino acid from the wild type. It does not affect the amino acid sequence of resultant proteins. For example-

            Point mutation (substitution) in HbA allele at second letter of 6th codon results HbS allele. HbS allele has 6th codon GTG encoding valine (instead of normal codon GAG that encodes glutamate) in the ?- chain of hemoglobin.

# Option B- likely to occur: The point mutation that creates a premature STOP codon is called a nonsense mutation. For example, the change in UGG to UGA (UGG = Tyr, UGA = STOP) is a non-sense mutation. Appearance of a stop codon causes premature termination of translation, thus resultant protein is shorter than the wild-type protein and have same amino acid sequence.

# Option C- likely to occur: The point mutation that does not change amino acid sequence is called a Silent Mutation. Silent point mutation arise due to substitution of one base with another base AND the mutated codon codes the same amino acid as wild type. It does not affect the amino acid sequence of resultant proteins. For example-

            CCU, CCC, CCA and CCG all encode for the same amino acid.

So, a mutation that changes the last letter of the codon does not change amino acid sequence.

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