When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by
A) a specific characteristic of the ribosome itself, which distinguishes free ribosomes from bound ribosomes.
B) a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.
C) moving through a specialized channel of the nucleus.
D) a chemical signal given off by the ER.
E) a signal sequence of RNA that precedes the start codon of the message.

Question

Quizplus · Accepted Answer

Ribosomes are directed to the ER membrane by a signal recognition particle (SRP) that recognizes a signal sequence in the emerging polypeptide and brings the ribosome to a receptor protein in the ER membrane. This allows for the proper localization and insertion of secretory or membrane proteins into the ER membrane.

When Translating Secretory or Membrane Proteins, Ribosomes Are Directed to the ER