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Practice MCAT Question - Q58 - Answer!

Insulin is a very small protein containing 51 amino acids in two chains linked together by disulfide bridges. What level of complexity best describes this protein?

A.  Primary structure
B.  Secondary structure
C.  Tertiary structure
D.  Quaternary structure

The correct answer is (D). When more than one chain of amino acids is present in a protein, their interaction reflects quaternary structure. The fact that insulin is a “small” protein may mislead students into incorrectly selecting choice (A) (primary structure), which refers to the protein chain’s sequence of amino acids.

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