Enzyme reaction models. Illustration of two common models for the mechanism of enzyme reactions. In both models, the substrate molecule (blue) attaches to the active site on the enzyme molecule (red), forming an enzyme-substrate complex (right). At top, in the lock-and-key model, the substrate is the same shape as the active site. At bottom, in the induced-fit model, the substrate triggers a change in the shape of the active site, allowing the reaction to take place. An enzyme is a biological catalyst, increasing reaction rates without itself reacting or changing. For this artwork with labels, see image C023/8717.
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