During the synthesis of proteins on the rough endoplasmic reticulum (RER) signal peptidase cleaves the hydrophobic signal sequence
A) immediately after signal recognition protein (SRP) is bound.
B) when the SRP docks with the SRP receptor.
C) simultaneously with the release of the ribosome.
D) as the polypeptide chain is translocated through the membrane.
E) as the protein is secreted through the plasma membrane.

Question

Quizplus · Accepted Answer

Signal peptidase cleaves the hydrophobic signal sequence as the polypeptide chain is translocated through the membrane of the rough endoplasmic reticulum. The signal sequence acts as a signal for the translocation machinery to target the protein to the ER membrane, and once translocation is complete, the signal peptide needs to be removed for the protein to properly fold and function. Signal peptidase specifically cleaves the peptide bond between the signal sequence and the mature protein, freeing the mature protein to continue its journey into the lumen or membrane of the ER.

During the Synthesis of Proteins on the Rough Endoplasmic Reticulum