01Enzymes are shaped catalysts
Most enzymes are proteins whose 3D shape creates an active site — a pocket that fits a specific substrate. The fit depends on the R groups lining the pocket: their charge, polarity and size.
The modern view is induced fit: the active site is flexible and tightens around the substrate once it binds, straining bonds and making reaction easier.
02Specificity
Because the active site's shape and chemistry must match, each enzyme works on one substrate or a narrow family. Sucrase breaks sucrose, not lactose.
Names ending in -ase usually signal an enzyme.
03Notebook box
Enzyme + substrate ⇌ enzyme-substrate complex → enzyme + product. The enzyme is unchanged and reused.
Worked example: A mutation swaps a negatively charged amino acid in the active site for a nonpolar one. Predict the effect. → The substrate, which binds through charge attraction, may no longer fit, reducing or eliminating activity.