Concept:Quaternary structure only exists if a functional protein requires
multiple, separate polypeptide chains aggregating together.
Solution:- Myoglobin is the oxygen-storing protein found exclusively in muscle tissue.
- Structurally, it consists of just a single, highly folded polypeptide chain (containing one heme group).
- Because it is only a single chain, it functionally maxes out at the Tertiary level of structure. It physically does not have a Quaternary structure.
Why other options are incorrect (they DO have Quaternary structure):- Hemoglobin: Classic tetramer consisting of exactly 4 separate chains (2 alpha, 2 beta).
- Antibodies: Complex Y-shaped molecules consisting of 4 chains (2 heavy, 2 light).
- DNA Polymerase III: A massive, multi-subunit enzymatic complex (holoenzyme) requiring several different chains to function together.
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