Polypeptides emerging from the ribosome must fold into stable three-dimensi
onal structures and maintain that structure throughout their functional Lif
etimes. Maintaining quality control over protein structure and function dep
ends on molecular chaperones and proteases, both of which can recognize hyd
rophobic regions exposed on unfolded polypeptides. Molecular chaperones pro
mote proper protein folding and prevent aggregation, and energy-dependent p
roteases eliminate irreversibly damaged proteins. The kinetics of partition
ing between chaperones and proteases determines whether a protein will be d
estroyed before it folds properly. When both quality control options fail,
damaged proteins accumulate as aggregates, a process associated with amyloi
d diseases.