What are enzymes and how do they work?

You might have heard enzymes referred to as 'biological catalysts'. This means, just like a catalyst you might add to a reaction in a chemistry practical, these proteins function to speed up reactions in a biological system. Enzymes are globular proteins, meaning the protein chain is folded into a tertiary structure to form a three dimensional (generally rounded) shape. This 3D shape includes an active site, which is a specific complementary shape to one particular substrate, and is where the catalysis takes place. You can think of it like a lock and key mechanism, in which the shape of the substrate (the key) must match the shaped of the active site (the lock). This depends on many interactions such as hydrogen bonding and van der Waals forces. The enzyme catalyses the reaction of substrate to product by lowering the activation energy barrier for the reaction to occur, for example by causing a conformational change.