Cell Division Proteolysis: Ubiquitin Pathway Role Explained

During cell division, targeted protein degradation via the ubiquitin-proteasome system regulates cyclin levels and checkpoints. The correct answer is option 4: Ubiquitin pathway.

Correct Answer

Option 4: Ubiquitin pathway.
The ubiquitin-proteasome system tags proteins like cyclins with polyubiquitin chains via E1-E2-E3 enzymes, targeting them for 26S proteasome degradation. Essential for mitotic exit by destroying cyclin B and securin.

Option Analysis

Option 1: Amino Acyl Synthetase Pathway

Aminoacyl-tRNA synthetases charge tRNAs for protein synthesis, not degradation. They activate amino acids for translation, unrelated to proteolysis.

Option 2: Restriction Endonuclease Pathway

Restriction endonucleases cleave foreign DNA in bacteria for defense. They have no role in eukaryotic protein degradation during cell division.

Option 3: ATPase Pathway

ATPases hydrolyze ATP for energy or transport (e.g., 19S proteasome cap uses ATP for unfolding). Not a specific proteolysis pathway; ubiquitin drives selectivity.

Option 4: Ubiquitin Pathway (Correct)

APC/C E3 ligase ubiquitinates cell cycle regulators during mitosis, enabling precise timing of degradation for anaphase and cytokinesis.

Exam Relevance

Ubiquitin questions test cell cycle regulation; APC/C specificity distinguishes it from general proteolysis.