What determines enzyme specificity?

Enzyme specificity arises from the precise complementarity between the enzyme active site and its substrate. The active site is a three-dimensional pocket with specific amino acid residues that position catalytic groups and bind substrate through multiple interactions (hydrogen bonds, ionic interactions, hydrophobic contacts). The lock-and-key model proposes rigid complementarity, while the induced fit model (more accurate) describes conformational changes upon substrate binding that optimize interactions. Specificity ranges from absolute (one substrate) to group specificity (related substrates) to broad specificity. Enzyme specificity ensures metabolic reactions occur with correct substrates without side reactions.