What is the primary function of ubiquitin in protein metabolism?

A To synthesize new proteins
B To degrade damaged or misfolded proteins ✓
C To regulate protein folding
D To transport proteins across cell membranes

Explanation

Ubiquitin is a small protein that marks damaged or misfolded proteins for degradation by the proteasome, helping to maintain protein homeostasis.

Mnemonic

Ubiquitin = 'ubiquitous' marker for degradation

Source

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