degradation

Meaning: Degradation is the enzyme-catalyzed breakdown of a biomolecule into smaller pieces. For macromolecules it is often hydrolysis: proteases cut peptide bonds and nucleases cut phosphodiester bonds. In cells, many proteins are tagged with ubiquitin and digested by the proteasome, which uses ATP; others are broken down in lysosomes by acid hydrolases. Fuels are degraded by catabolic pathways such as glycolysis and β-oxidation. Edman degradation is a separate lab method that removes N-terminal residues one at a time to sequence a peptide.

On the MCAT: Passages give a protein or mRNA with a short or long half-life, or a mutation that blocks ubiquitin tagging, and ask how its level or activity changes (it accumulates, so its signal persists). Cyclin degradation, which lets the cell cycle advance, is a classic example.

Common confusion: Degradation is not denaturation. Denaturation disrupts folding but leaves peptide bonds intact; degradation breaks covalent bonds. Peptide hydrolysis is thermodynamically favorable but very slow without a catalyst, which is why proteases are needed.