Enzymes as Catalysts

How do enzymes catalyse reactions?

Enzyme catalysed reactions occur at a particular place on the surface of the large enzyme molecule called the active site (as in heterogeneous catalysts). The reactant molecule, often called the substrate, is able to form relatively weak, temporary bonds to the enzyme at the active site.

The enzyme lipase catalyses the breakdown of fatty acids. Notice its defintie 3 dimensional shape.

 

How does it fit?

It can do this because it has a shape that fits the shape of the active site AND because the structure of the reactant molecule enables it to form intermolecular attractions with sections of the protein chain that are near to it. In order to interact in this way, covalent bonds within the substrate molecule need to stretch or become distorted. This movement weakens these bonds and allows them to break more readily. Product molecules are therefore formed that do not have the shape or structure to be attracted to the protein chain and are released from the active site. This site is now available to catalyse the breakdown of another substrate molecule.

Flow diagram

Enzyme and substrate
 
Enzyme–substrate complex
 
Enzyme–product complex
 
Enzyme and products