Final answer:
Retrotranslocation is a process that retrotranslocates misfolded proteins from the ER into the cytosol for degradation by the proteasome, which accounts for the association with N-linked glycans and polyubiquitination. This pathway helps maintain cellular homeostasis by removing defective proteins and is part of the ER-associated degradation (ERAD) system.
Step-by-step explanation:
How is Retrotranslocation believed to account for N-linked glycans and polyubiquitination? The correct answer is C) Drives degradation of misfolded proteins in the proteasome. During the quality control process within the cell, misfolded proteins in the endoplasmic reticulum (ER) that are destined for destruction are retrotranslocated back into the cytosol. This process is believed to be associated with N-linked glycans and polyubiquitination.
N-linked glycosylation is the attachment of oligosaccharides to the nitrogen atom of an asparagine side chain in proteins. This modification typically begins in the rough endoplasmic reticulum (RER) and continues in the Golgi apparatus. Polyubiquitination is a process where multiple ubiquitin molecules are attached to a protein, usually signaling that the protein needs to be degraded by the proteasome.
Proteins that are misfolded are recognized by ER quality control, polyubiquitinated, and then retrotranslocated through the ER membrane back into the cytosol, where they are degraded by the proteasome. Glycoproteins that fail quality control may also be demannosylated, which serves as a further signal for degradation. Thus, retrotranslocation is critical for the ER-associated degradation (ERAD) pathway, which maintains cellular homeostasis by degrading defective proteins that could otherwise accumulate and harm the cell.