substrate (biochemistry)

In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate(s). The substrate binds with the enzyme's active site, and an enzyme-substrate complex is formed. The substrate is broken down into a product and is released from the active site. The active site is now free to accept another substrate molecule. An example of a substrate would be milk and the enzyme added would be rennin which causes milk to set. Another example would be the reaction of catalase in the decomposition of hydrogen peroxide.2 H2O2 → 2 H2O + O2.
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