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Enzymes are proteins that serve as catalysts, chemical agents that change the rate of a reaction without being consumed by the reaction.

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Enzymes Enzymes are proteins that serve as catalysts, chemical agents that change the rate of a reaction without being consumed by the reaction. An enzyme catalyzes the reaction by lowering the activation energy barrier which enables the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures. However, an enzyme can't make an endergonic reaction exergonic or vice-versa. They can only speed up reactions that would eventually occur on their own. An enzyme's substrate is the reactant an enzyme acts on. An enzyme-substrate complex is formed when the enzyme binds to its substrate(s). When the enzyme-substrate complex is formed, the catalytic function of the enzyme converts the substrate to the product of the reaction. An enzyme can recognize its specific substrate even among isomers. ...read more.


However, when the substrate enters the active site, there isn't a perfect fit. Interactions between its chemical groups and those on the amino acids of the protein cause the active site to fit more closely around the substrate which is known as an induced fit. Induced fit brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction. The process occurs so quickly that one enzyme can act upon a thousand substrate molecules a second while other enzymes are even faster. Since most metabolic reactions are reversible, an enzyme can catalyze both the forward and reverse reactions. There is an optimal temperature and pH for each enzyme at which it is most active. In humans the optimal temperature is around 35-40� C while in bacteria that live in hot springs the optimal temperature is 70�C or higher. ...read more.


For example, the competitive inhibitor mimics a substrate and competes for admission into the active site. This reduces the productivity of enzymes by blocking the substrates from entering active sites. On the other hand, a noncompetitive inhibitor doesn't compete with the substrate. Instead, it binds to a different part of the enzyme and that interaction causes the enzyme molecule to change its shape so that its active site no longer functions. There is also allosteric regulation of enzymes in which a protein's function at one site is affected by the binding of a regulatory molecule to a separate site that may either inhibit or stimulate an enzyme's activity. Cooperativity is an interaction of the constituent subunits of a protein whereby a conformational change in one subunit is transmitted to all the others. Conversely, in feedback inhibition a metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme that acts early in the pathway. ...read more.

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