Enzymes are the catalysts for a large number of biochemical reactions vital for survival of living organisms. Without enzymes, such reactions will occur very slowly or not occur at all, due to high activation energy requirements. Enzymes provide an alternate pathway for these reactions, thereby moving them to completion. Interestingly, enzymes are not used up during the reaction. The reactants, called substrates (S), combine with enzymes (E) to form substrate-enzyme complexes (ES), which then form the final products (P).
S + E -> SE -> P + E
The enzyme is regenerated after the reaction completion and is used again for next set of reaction. Enzymes are also highly selective and a particular enzyme will catalyze only a particular reaction. All these characteristics, along with their central role in catalysis, make them vital for existence of living organisms.
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