catalyst: Enzymes: Natural Catalysts

Enzymes: Natural Catalysts

Enzymes are the commonest and most efficient of the catalysts found in nature. Most of the chemical reactions that occur in the human body and in other living things are high-energy reactions that would occur slowly, if at all, without the catalysis provided by enzymes. For example, in the absence of catalysis, it takes several weeks for starch to hydrolyze to glucose; a trace of the enzyme ptyalin, found in human saliva, accelerates the reaction so that starches can be digested. Some enzymes increase reaction rates by a factor of one billion or more.

Enzymes are generally specific catalysts; that is, they catalyze only one reaction of one particular reactant (called its substrate). Usually the enzyme and its substrate have complementary structures and can bond together to form a complex that is more reactive due to the presence of functional groups in the enzyme, which stabilize the transition state of the reaction or lower the activation energy. The toxicity of certain substances (e.g., carbon monoxide and the nerve gases) is due to their inhibition of life-sustaining catalytic reactions in the body.

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