Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologyhardmcq1 pt

Both polypeptide chains of a two subunit human protein accumulate abundantly inside engineered E. coli, yet purified samples show no biological activity. Assuming the coding sequences are correct, what best explains the failure?

A.The subunits failed to fold and assemble into the correct quaternary structure in the bacterial cytoplasm
B.Bacterial ribosomes introduced mutations while translating the two messages
C.Two different mRNAs were translated instead of one combined transcript
D.The cells degraded their plasmids after making the first batch of protein

Explanation

Core Concept

Activity of multichain eukaryotic proteins requires precise folding plus stable association of the subunits, often including disulfide bonds. The reducing bacterial cytoplasm hinders disulfide formation, and misfolded chains frequently aggregate into inclusion bodies. Abundant full length translation therefore does not guarantee a native, active molecule. Periplasmic targeting, refolding steps, or a eukaryotic host can restore function.

Correct Answer

AThe subunits failed to fold and assemble into the correct quaternary structure in the bacterial cytoplasm

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