Biology · Ch 6 — Biomolecules
Mechanism of Enzyme Action
Mechanism of Enzyme Action
The basic mechanism by which an enzyme catalyses a reaction starts with the substrate (or substrates) binding to the enzyme's active site — the specific region of the enzyme surface shaped to combine with that substrate. This binding shifts the distribution of electrons within the chemical bonds of the substrate, which in turn drives the reaction that converts substrate into product. Once formed, the product is released from the enzyme's surface, regenerating the free enzyme so that it can bind another substrate molecule and repeat the cycle.
Two models have been proposed to explain how the enzyme–substrate complex forms:
Lock-and-key model: First proposed by Emil Fischer in 1894, this model explains an enzyme's specificity for a single substrate through a simple analogy — the enzyme is imagined as a lock, and the substrate as a key. Only a key of exactly the right shape (the correctly sized substrate) fits into the keyhole (the active site) of that particular lock (the enzyme); the active site is treated as a rigid, pre-formed shape. …
What this figure shows. A schematic showing a substrate molecule binding to the active site of an enzyme to form an enzyme-substrate complex, which reacts and releases product(s), leaving the enzyme unchanged and free to bind another substrate m …
What this figure shows. A cartoon of a padlock (representing the enzyme) with a keyhole shaped to exactly fit only one specific key (representing the substrate), illustrating that only a substrate of the correct shape fits an enzyme's …
What this figure shows. A sequence showing an enzyme's active site as a flexible pocket that reshapes as the substrate approaches and binds, ending with the active site moulded closely around the bound substrate, in contrast to a rigid lock-and-key activ …