Enzymes

Enzymes

• Catalyst: a substance that increases the rate of a chemical reaction and is not changed in the process.
• Enzymes: proteins that function as biological catalysts.
• Enzymes are important in all living organisms as chemical reactions that take place in organisms normally happen too slowly to keep the organism alive - unless speeded up by enzyme action.

Enzyme action

• 
• Enzymes work on substances called substrates. The reaction takes place on a part of the surface of the enzyme called the active site.
• The substrate enters the active site to form an enzyme-substrate complex. The enzyme then produces the product(s).
• Only substrate molecules with a shape that fits in to the active site will take part in the reaction catalyzed by the enzyme.

Factors affecting enzyme action

• Temperature
• Increasing the temperature of an enzyme-controlled reaction increases the rate of reaction up to a maximum, which occurs at the optimum temperature.
• This is because greater kinetic energy is causing a greater number of effective collisions between the active site of the enzyme and substrate molecules.
• At higher temperatures the rate of reaction decreases quickly until it stops acting as a catalyst.
• This is due to a change in the shape of the active site meaning that the substrate can no longer fit - the enzyme is denatured.
• pH
• Most enzymes work best at one value of pH.
• At some values of pH the shape of the active site changes to that the substrate molecules no longer fit - denaturation of the enzyme.