The first step in protein synthesis that distinguishes a protein to be secreted from one to be retained in the cytoplasm is:
A) attachment of the ribosome to a membrane.
B) removal of signal sequences by signal peptidase.
C) binding of the signal recognition particle to the signal sequence.
D) binding of the fmet-tRNA to the ribosome.
E) binding of specialized ribosomes to the mRNA.

Question

Quizplus · Accepted Answer

The binding of the signal recognition particle (SRP) to the signal sequence on the growing polypeptide distinguishes a protein to be secreted from one to be retained in the cytoplasm. The SRP then binds to its receptor on the endoplasmic reticulum (ER) membrane, where the ribosome is docked for continuation of protein synthesis. The removal of signal sequences by signal peptidase occurs once the protein is translocated into the ER lumen.

The First Step in Protein Synthesis That Distinguishes a Protein