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. This is because enzymes are proteins and proteins are macromolecules with unique three-dimensional shapes that result from their amino acid sequences. The active site is the restricted region of the enzyme molecule that binds to the substrate, typically a pocket or groove on the surface of the protein. It’s usually formed by few of the enzyme’s amino acids and the rest of the protein molecules provide a framework that determines the form of the active site. Usually, the substrate is held in the active site by weak interactions such as hydrogen bonds and ionic bonds. 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.

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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. The optimal pH for most enzymes is usually in the range of pH 6-8 with exceptions.

Many enzymes require cofactors, nonprotein ...

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