Substrate (Biology) — Definition & Role

Active Sites

Enzymes have a specific location where reactants are brought together to react. These reactants are called substrates and the specific binding location is called the active site.

The substrate molecule binds to the active site. Think of it like putting a hand in a glove or like putting a key in a lock. It fits perfectly.

Binding Models

There are two different ways the enzyme and its substrate can fit together: the lock-and-key model and the induced fit model. Both of these are shown below.

• Lock-and-Key Model: The shape of the active site matches the specific substrate that it reacts with. The substrate fits into the active site perfectly, similar to how a key fits into a lock.
• Induced Fit Model: The active site will undergo induced fit to mold itself more closely to the substrate. Think of this like putting your hand into a plastic glove. Your hand is the substrate and the glove is the active site. The glove changes shape as you place your hand into it, much like how the active site changes shape to fit the substrate.

After binding to the active site, the substrates form new compounds called products.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Enzyme}}$ : A protein that acts like a catalyst. It speeds up biological reactions but is not used up during the reaction

$\color{#8925AE}{\text{Activation Energy}}$ : Minimum amount of energy needed to begin a chemical reaction

$\color{#8925AE}{\text{Catalyst}}$ : A substance that speeds up reactions but is not used up during the reaction

$\color{#8925AE}{\text{Substrate}}$ : Molecules that a specific enzyme binds to and recognizes. They are transformed during the reaction

How Do Enzymes Work With Reactants?

An enzyme acts to catalyze or speed up a chemical reaction. To look at how this is done, we'll need to keep some important terms in mind:

Here are those terms in pictures:

Notice how the substrates and enzyme fit together perfectly. In this picture, we have one substrate with a rounded end and one with a pointy end. They fit exactly into the matching active site shapes.

This fit with the enzyme is extremely specific. It is often referred to as a lock and key model. The correct key (substrate) has to fit into the correct lock (enzyme) for the reaction to work.

This lock and key business is how enzymes work their magic. They bring reactants close enough together for the reaction to occur quickly.

However, it is important to note: Reactions do not need enzymes to occur. That is, reactions can still occur without enzymes. They just occur very slowly.

(Video) How Enzymes Work

by RicochetScience

Substrates, active sites, enzyme-substrate complexes... There are lots of terms involved in enzymatic reactions. This short video gives an overview of the parts involved in an enzyme-regulated reaction.

Reactants and Enzymes

In an enzyme-catalyzed reaction, the term substrate means the same thing as reactant. A reactant is the material that is used up in the reaction.

Substrates fit into the active site of the enzyme. The more substrate we have, the easier it is for it to bind to the enzyme. After the reactants go through the chemical reaction, they emerge as products.