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An enzyme's active site binds with substrates in Lock and Key model (image 1 of 3). To catalyse chemical reactions enzymes must achieve the right fit between parts, including the reactant molecules the enzyme works on, known as substrates. There is a very specific region on an enzyme molecule, usually an indentation or pocket called the active site, to which a substrate will bind and where the reaction process occurs. But in order for this to happen, there must be a compatible fit between the shape of the enzyme's active site and the shape of its substrate. One model that describes this fit, called the lock and key model, compares the enzyme binding to a substrate to a key fitting into a lock.
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