Mode of action of enzymes

Basic Facts about Enzymes

Enzymes are biological catalysts that speed up biochemical reactions in the body.
They’re made of proteins and are highly specific, meaning each type of enzyme can only catalyse one reaction.
Enzymes aren’t consumed in the reaction and can be used repeatedly.
They are sensitive to changes in temperature and pH, showing optimal activity under specific conditions.

The Lock and Key Model

Each enzyme has an active site which fits the shape of a specific substrate.
This follows the lock and key model: the active site (the lock) can only be ‘opened’ by the correct substrate (the key).

Induced Fit Model

The induced fit model elaborates on the lock and key, suggesting active sites are more flexible.
On collision with the substrate, the enzyme slightly changes its shape (conformational change) to achieve a tighter fit.
This shape change induces stress on the substrate’s bonds, facilitating the reaction.

Mode of Action of Enzymes

Enzymes bind to their substrate forming an enzyme-substrate complex.
This binding often involves H-bonds or ionic interaction between the substrate and R groups in the enzyme’s active site.
After the reaction completes, the enzyme releases the products, then returns to its original conformation.
Enzymes can speed up reactions by:
- Lowering the activation energy needed for a reaction to occur.
- Bringing two substrates together in the right orientation to react.
- Inducing a conformational shift in the substrate to destabilise existing bonds.

Effects of Environmental Factors

Temperature: Enzyme activity increases with temperature until a peak (optimal temperature), after which the enzyme denatures and loses its function.
pH: Each enzyme has an optimal pH at which it performs best. Variation from this pH could cause denaturation.
Enzyme concentration: Enzyme activity increases with concentration, provided there’s enough substrate.
Substrate concentration: If enzyme concentration is constant, activity increases with substrate concentration until a saturation point where all the enzymes’ active sites are occupied.