Question

In yeast cells, protein transport across the endoplasmic reticulum membrane occurs __________

(a) perpendicularly

(b) discontinuously

(c) co-translationally

(d) post-translationally

This question was addressed to me in an international level competition.

Enquiry is from Cytoplasmic Membrane Systems topic in division Cytoplasmic Membrane Systems of Cell Biology

Answer 1

Correct choice is (d) post-translationally

Explanation: Polypeptide is synthesized in the ribosome and if appropriate signal is present in its C-terminal it moves to the ER membrane during the synthesis, this is called co-translational movement. In post-translational movement, the nascent polypeptide reaches the ER membrane after complete synthesis. Unlike mammalian cells post-translational movement of the polypeptides is observed in the yeast cells.