An '''enzyme''' is a [[protein]] produced by a living organism that functions as a [[catalyst]]. Enzymes increase the speed and likelihood of chemical reactions within an organism's body by lowering the activation energy necessary for a reaction to occur. This happens because the enzyme selects the particular configuration of the substrate and bends the bonds into the energetically-favorable orientation, with a consequent decrease in entropy. They are essential to all cellular functions, and most life could not exist without them, although viruses lack enzymes, but use them from their host cell.<ref>http://www.medterms.com/script/main/art.asp?articlekey=3266</ref>
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An '''enzyme''' is a [[protein]] produced by a living organism that functions as a [[catalyst]].
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== Mechanism ==
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Enzymes increase the speed and likelihood of chemical reactions within an organism's body by lowering the activation energy necessary for a reaction to occur. This happens because the enzyme selects the particular configuration of the substrate and bends the bonds into the energetically-favorable orientation, with a consequent decrease in entropy. They are essential to all cellular functions, and most life could not exist without them, although viruses lack enzymes, but use them from their host cell.<ref>http://www.medterms.com/script/main/art.asp?articlekey=3266</ref> The active site, a three-dimensional structure, is the only region of the enzyme that binds to the substrate. It permits only a particular substrate to bind to the site.<ref>https://www.britannica.com/science/enzyme</ref>