Scientists have found that polypeptides which are normally synthesized in the endoplasmic reticulum are about 20 amino acids longer when they are synthesized by ribosomes not attached to the endoplasmic reticulum. What is a possible explanation for the greater length of these polypeptides?
A) Ribosomes attached to the endoplasmic reticulum require fewer amino acids to function.
B) The 20 amino acids serve as a signal (peptide) sequence that directs the forming polypeptides to the endoplasmic reticulum, where they are cleaved off during processing.
C) The 20-amino-acid sequence helps the endoplasmic reticulum package these proteins for shipping to the Golgi.
D) The protein has a different function in the cytosol than in the endoplasmic reticulum.

Question

Quizplus · Accepted Answer

The 20 amino acids serve as a signal (peptide) sequence that directs the forming polypeptides to the endoplasmic reticulum, where they are cleaved off during processing. This is a common mechanism of targeting proteins to specific organelles in the cell. The extra amino acids allow the polypeptide to be recognized by the endoplasmic reticulum and transported to the correct location for further processing.

Scientists Have Found That Polypeptides Which Are Normally Synthesized in the Endoplasmic