Succinate is converted to fumarate by the enzyme dehydrogenase. This reaction can be inhibited by adding malonate. a) What are enzymes and what are their function? Use this information to explain how malonate acts as an inhibitor.

a) What are enzymes and what are their function? Use this information to explain how malonate acts as an inhibitor.

What are enzymes? Enzymes are proteins that act as catalysts in living cells. Catalysts increase the rate at which chemical reactions occur without being consumed or permanently altered in reactions. As a catalyst, an enzyme can facilitate the same chemical reaction over and over again.

Why are they important? Enzymes speed up reactions and prevent toxin build-up.

What is the structure of an enzyme? Like all proteins, enzymes are made of one or more long chains of amino acids. Each enzyme has a unique sequence of amino acids that cause it to fold into a specific shape. Each enzyme has an active site, which is a cleft that allows the substrates to interact, so that the reaction can take place. Because the enzyme's active site is specific and unique, each enzyme is specific in the reaction it can catalyse; generally one reaction per molecule at a given time, almost like a lock and key.

When the enzyme and substrate form a complex, structural changes occur so that the active site fits precisely around the substrate. The reaction takes place and the product, being a different shape to substrate, moves away from active site. The active site then returns to the original shape.

Inhibitors Enzyme inhibitors reduce the rate of an enzyme-catalysed reaction by interfering with the enzyme in some way. This effect may be temporary or permanent. There are different types of inhibitors. Competitive enzyme inhibitors work by preventing the formation of enzyme-substrate complexes because they have a similar shape to the substrate molecule. This means that they fit into the active site, but remain unreacted because they have a different structure to the substrate. This means less substrate molecules can bind to the enzymes so the reaction rate is decreased.

Non-competitive enzyme inhibitors work not by preventing the formation of enzyme-substrate complexes, but by preventing the formation of enzyme-product complexes. So they prevent the substrate from reacting to form product. Usually, non-competitive inhibitors bind to a site other than the active site, called an allosteric site. This alters the 3D tertiary structure of the enzyme, so that it can no longer catalyse a reaction.