Apentix/AP Biology/Unit 1: Chemistry of Life/Question
AP Biologymediummcq1 pt

Hemoglobin needs four separate polypeptide chains, each cradling a heme group, before it can carry oxygen efficiently. Which level of protein structure does this assembly represent, and what holds it together?

A.Quaternary structure, held by noncovalent interactions among the four subunits
B.Primary structure, held by the sequence of amino acids in one chain
C.Secondary structure, held by hydrogen bonds within each chain's backbone
D.Tertiary structure, held by bonds among side chains inside one folded chain

Explanation

Core Concept

Any organization involving more than one polypeptide chain is quaternary structure. Hemoglobin pairs two alpha and two beta subunits, and hydrophobic interactions, hydrogen bonds, and ionic contacts at the subunit interfaces hold the tetramer together while each chain carries its own iron-containing heme. Sequence defines primary structure, backbone hydrogen bonding defines secondary structure, and within-chain side-chain interactions define tertiary structure, so a four-chain assembly can only be quaternary.

Correct Answer

AQuaternary structure, held by noncovalent interactions among the four subunits

More Unit 1: Chemistry of Life practice questions

Try a random question →

Practice more AP Biology questions with full explanations

Practice Unit 1: Chemistry of Life Questions →