Enzyme does not act by

Enzyme decreases the activation energy & thus they increase the rate of reaction. Mostly in Enzyme-Substrate (ES) interactions, non covalent interactions are formed (Hydrogen, Hydrophobic & Ionic bonds). Gibb's Free Energy graph for enzyme catalyzed and enzyme uncatalyzed reaction. On X- axis, reaction progress taken (i.e. S getting conveed to P). For any spontaneous reaction, S has more free energy as compared to P. For S to be conveed to P, first S has to acquire Activation energy (DG uncatalyzed) and reach high energy state (Transition state). Only then it can be conveed to P.