An enzyme as a catalyst.
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   The enzyme sucrase catalyzes the hydrolysis of sucrose.
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   The  starting  molecules  ( sucrose and H[2]O ) in a chemical reaction
   are called reactants or substrates.
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   The  molecules  produced  by the reaction ( glucose and fructose ) are
   called products.
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   The  enzyme  does  not  take  part  in  the  reaction, but serves as a
   catalyst, speeding up the reaction.