Enzymes are protein-based catalysts found in living things.

The active site is a cleft or crevice in an enzyme where substrates bind.

Only substrates whose shape fits the active site can react.

The lock and key hypothesis suggests that the substrate fits into the enzyme’s active site in the same way in which a key fits into a lock. The shape of the substrate and the active site are perfectly complementary to each other. 

The lock and key hypothesis is depicted below.

Enzymes are made up of amino acids so they contain chiral centres - this makes the shape of their active sites very specific so that only one enantiomer can properly fit in the active site.

Enzymes that only bond to one enantiomer of a substrate are said to be stereospecific.

Computer modelling streamlines enzyme research by aiding in the discovery of new inhibitors and optimizing drug design. It enables virtual screening, high-throughput screening, and predicting the best-fitting enantiomer for an enzyme's active site, reducing the need for extensive synthesis and testing.

Competitive enzyme inhibitors are drug molecules that have a similar shape to the enzyme's substrate. These molecule will bind to the enzyme's active site and block it, stopping the reaction.

This is the mode of action of some drugs, for example, penicillin inhibits the enzymes that control the building of cell walls in bacteria.

The 3D shape of a protein is vital to how it functions.

For example, changing the shape of an enzyme's active site can stop it working.

Competitive inhibition can be overcome by increasing the substrate concentration. In competitive inhibition, the inhibitor competes with the substrate for the enzyme's active site. By increasing the substrate concentration, the likelihood of the substrate binding to the active site increases, as it outnumbers the inhibitor molecules.