Enzymes are biological catalysts — proteins that speed up biochemical reactions without being consumed. The mechanism by which enzymes work explains both their remarkable efficiency and their specificity (each enzyme catalyzes only a specific reaction).
Enzymes can increase reaction rates by factors of 10⁶ to 10¹² — a reaction that would take a million years spontaneously can occur in a millisecond with the right enzyme. This is the power of biological catalysis.
1. Substrate Binding: The enzyme has a specific region called the Active Site — a three-dimensional pocket or groove on its surface with a shape and chemical environment complementary to the specific substrate molecule.
The substrate molecule binds to the active site, forming an Enzyme-Substrate (ES) Complex. This binding is highly specific.
2. Catalysis: Once the ES complex forms, the enzyme either:
This lowers the Activation Energy required for the reaction, dramatically speeding it up.
3. Product Release: The reaction occurs, substrates are converted to products, and the products are released from the active site. The enzyme is unchanged and free to catalyze the next reaction.
1. Lock and Key Model (Fischer, 1894): The enzyme (lock) and substrate (key) have perfectly complementary, rigid shapes. The substrate fits exactly into the active site.
2. Induced Fit Model (Koshland, 1958) — More Accepted: The active site is NOT perfectly rigid. When the substrate approaches, the enzyme's active site changes shape slightly to fit the substrate better — like a hand fitting into a glove. This model better explains enzyme behavior.
Enzyme action is specific because only a substrate with the correct size, shape, and chemical properties can bind to the active site. The highly specific 3D shape of the active site acts like a molecular recognition system.
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