What is the primary mechanism by which the ubiquitin-proteasome pathway regulates protein degradation in eukaryotic cells?

A Tagging proteins with ubiquitin molecules for proteasomal degradation ✓
B Inhibiting protein synthesis through the regulation of translation initiation factors
C Enhancing protein folding through molecular chaperones to prevent degradation
D Directly degrading proteins through enzymatic cleavage

Explanation

The ubiquitin-proteasome pathway is a key regulatory mechanism for protein degradation in eukaryotic cells, involving the tagging of target proteins with ubiquitin molecules to mark them for degradation by the proteasome.

Source

Alberts et al., Molecular Biology of the Cell
Protein Metabolism Biochemistry Protein Degradation Hard MEDICAL Confidence: high