[Campbell Biology P.407] Based on Figure 17.27 b , how do a 1-nucleotide-pair deletion and a... | Practice Question

Based on Figure 17.27 b , how do a 1-nucleotide-pair deletion and a 3-nucleotide-pair deletion primarily differ in their effect on the resulting polypeptide?

  • A: Both cause a frameshift, but a 3-nucleotide deletion leads to a shorter polypeptide.
  • B: A 1-nucleotide deletion causes a frameshift, while a 3-nucleotide deletion typically results in the loss or gain of one amino acid without a frameshift.
  • C: A 3-nucleotide deletion always introduces a premature stop codon, while a 1-nucleotide deletion only changes one amino acid.
  • D: Both types of deletions only affect the mRNA sequence, not the protein sequence.

Explanation

A 1-nucleotide deletion causes a frameshift because it shifts the entire reading frame downstream, altering every subsequent codon and leading to a vastly different polypeptide and often a premature stop. In contrast, a 3-nucleotide deletion removes an entire codon or multiple codons in multiples of three , which means the reading frame downstream remains intact. This typically results in the loss of one or more specific amino acids, but the rest of the polypeptide sequence is usually unaffected, as stated in the figure notes.