Enzymes

Full Notes

Enzymes are proteins that catalyse biochemical reactions.

They lower activation energy by providing an alternative pathway for a reaction to occur.

Enzyme Active Sites and Stereospecificity

The part of an enzyme that binds to the substance reacting (the substrate) is called the active site and it has a specific shape.

Enzymes exhibit stereospecificity, meaning they only bind to one enantiomer of a substrate. This is because the 3D structure of the active site only fits one optical isomer correctly. (See Optical Isomerism for more detail)

This is really important in biology as many natural molecules (such as amino acids) show optical isomerism and can exist as enantiomers.

For example, if a drug is chiral, only one enantiomer may be effective.

Enzyme Inhibition and Drug Design

Drugs can inhibit enzymes by blocking the active site, meaning the substrate is no longer able to bind the enzyme and no catalysis can occur.

Computational Drug Design: Because enzymes are proteins they can have very complicated shapes and computers are often used to help model enzyme structures and help design inhibitors. This speeds up drug discovery for pharmaceuticals.

4. Summary

• Enzymes are protein catalysts that lower activation energy and speed up biochemical reactions.
• Active sites are stereospecific, so only one enantiomer of a substrate usually binds effectively.
• Drugs can act as competitive inhibitors by blocking active sites and stopping catalysis.
• Computational modelling helps design inhibitors that fit specific active sites.