MCAT® ExamBiological and Biochemical Foundations of Living SystemsHard
A patient is diagnosed with a rare genetic disorder that results in the accumulation of abnormally folded proteins within the endoplasmic reticulum (ER) of cells. This accumulation triggers an ER stress response, leading to apoptosis if the stress is prolonged. Which of the following cellular processes is most directly compromised by the initial accumulation of misfolded proteins in the ER?
- ADNA repair
- BGlycolysis
- CProtein secretion
- DMitochondrial respiration
Show answer & explanationAnswer & explanation
Correct answer: C. Protein secretion
The endoplasmic reticulum is the primary site for the folding, modification, and assembly of proteins destined for secretion or insertion into membranes. An accumulation of misfolded proteins directly impedes the normal processing and trafficking of these proteins, thus compromising protein secretion.
Why the other options are wrong
- A. DNA repair occurs in the nucleus and is separate from ER function.
- B. Glycolysis occurs in the cytoplasm and is not directly affected by ER protein folding issues.
- D. Mitochondrial respiration occurs in the mitochondria and is not directly compromised by ER protein folding, though severe ER stress can indirectly impact overall cell health.
Endoplasmic Reticulum Function
The endoplasmic reticulum (ER) is a network of membranes within eukaryotic cells involved in protein and lipid synthesis, folding, modification, and transport.
- Rough ER (RER): studded with ribosomes, involved in synthesis and folding of secreted and membrane proteins.
- Smooth ER (SER): involved in lipid synthesis, detoxification, and calcium storage.
- Misfolded proteins in RER trigger the unfolded protein response (UPR) and can lead to ER-associated degradation (ERAD) or apoptosis.
Memory trick: Misfolded proteins 'CLOG' the 'SECRETION' pathway.