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Models of enzyme function

There are several theories suggesting how enzymes decrease the activation energy of reactions.

One popular theory is called the lock-and-key hypothesis:

  1. The substrate (the key) binds to the active site of the enzyme (the lock).
  2. The substrate and active site have complementary shapes.

  3. This forms an enzyme-substrate complex (ES-complex).
  4. The ES-complex lowers the activation energy of the reaction, allowing it to occur.
  5. The products of the reaction do not fit the active site. They are quickly removed.
This enzyme catalyses the breakdown of a molecule into two parts. Other enzymes can join molecules together.
This enzyme catalyses the breakdown of a molecule into two parts. Other enzymes can join molecules together.

The lock-and-key hypothesis is a simple but inaccurate way of understanding enzyme function. The induced fit model is a more accurate version of the lock-and-key hypothesis.

In the induced fit model, the binding of the substrate causes the enzyme to change shape. The shape change activates the enzyme, enabling it to act as a catalyst.