Apentix/AP Biology/Unit 2: Cell Structure and Function/Question
AP Biologyhardmcq1 pt

A gene encoding a secreted hormone has just been switched on. Which sequence correctly describes how the growing polypeptide first reaches the endomembrane system?

A.Signal peptide emerges, SRP binds and stalls translation, the complex docks at the ER, then elongation resumes into the lumen
B.Translation completes in the cytosol before SRP escorts the finished hormone to the ER
C.The chain folds freely first, then signal peptidase ships it onward from the Golgi
D.SRP opens nuclear pores so the nascent chain grows straight into the ER

Explanation

Core Concept

As the N-terminal signal peptide exits the ribosome, signal recognition particle clamps onto it and pauses elongation. Docking at an ER receptor delivers the ribosome to a translocon channel, and translation resumes, threading the chain into the lumen. There the signal is clipped and folding begins, committing the hormone to the secretory pathway.

Correct Answer

ASignal peptide emerges, SRP binds and stalls translation, the complex docks at the ER, then elongation resumes into the lumen

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