Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologyeasymcq1 pt

In the beta-globin gene, the coding-strand triplet GAG mutates to GTG. Which outcome best describes the resulting protein?

A.A stop codon appears early, truncating the beta-globin polypeptide in half
B.Valine replaces glutamic acid at position six, giving hemoglobin S its sticky hydrophobic patch
C.Two extra bases shift the frame, altering every amino acid downstream
D.No amino acid changes because the code is redundant across all sixty-four triplets

Explanation

Core Concept

The single base swap changes one mRNA codon from GAG to GUG. GAG codes for glutamic acid, a negatively charged residue, while GUG codes for valine, which is hydrophobic. Surface valine patches allow deoxygenated hemoglobin molecules to polymerize into fibers that bend red blood cells into sickles.

Correct Answer

BValine replaces glutamic acid at position six, giving hemoglobin S its sticky hydrophobic patch

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