<P> In biology, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction . The active site consists of residues that form temporary bonds with the substrate (binding site) and residues that catalyse a reaction of that substrate (catalytic site). The active site is usually a groove or pocket of the enzyme which can be located in a deep tunnel within the enzyme, or between the interfaces of multimeric enzymes . An active site can catalyse a reaction repeatedly as its residues are not altered at the end of the reaction (they may change during the reaction, but are regenerated by the end). </P> <P> Usually, an enzyme molecule has only two active sites, and the active sites fit with one specific type of substrate . An active site contains a binding site that binds the substrate and orients it for catalysis . Residues in the binding site form hydrogen bonds, hydrophobic interactions, or temporary non-covalent interactions (van der Waals) with the substrate to make an enzyme - substrate complex . In order to function, the active site needs to be in a specific conformation and so denaturation of the protein by high temperatures or extreme pH values will destroy its catalytic activity . A tighter fit between an active site and the substrate molecule is believed to increase efficiency of a reaction . Most enzymes have deeply buried active sites, which can be accessed by a substrate via access channels . </P>

Where does the substrate attach to the enzyme
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