Enzyme does not act by ?

Ans. is 'c' i.e., Increasing activation energyEnzymes increase the rate of a biochemical reaction, therefore they are called catalysts of reaction.Now the question arises that how does they do that?In a chemical reaction, the substrate has to be conveed to a higher energy form (called transition form) before it can form the reaction products.The transition state is structurally an intermediate between the substrate and the product, and represents the highest energy arrangement of atoms. Therefore, it is unstable; once formed, it decomposes almost immediately to form the reaction product.So, this high energy intermediate acts as energy barrier, separating the substrates and the products.This barrier, called the free energy of action, is the energy difference between the energy of the substrates and high energy intermediates.In other words, initially some energy must be put into the substrate for conversion into transition state (high-energy intermediate); this is the free energy of activation.The enzymes speed up the chemical reaction by lowering the magnitude of the activation energy barrier, i.e., free energy of activation.Most enzyme-substrate combinations are mostly due to weak non-covalent interactions like hydrogen bond, hydrophobic interactions, ionic (electrostate) interaction and Vander waals forces.However, covalent catalysis involves the formation of a covalent bond between the amino acyl residues of active site of enzyme and substrate.Covalent catalysis is used by serine proteases (trypsin, chymotrypsine) which bind their substrate covalently at serine side chain.