Enzymes & Temperature

Enzymes are proteins and have a specific shape, held in place by bonds

• This is extremely important around the active site area as the specific shape is what ensures the substrate will fit into the active site and enable the reaction to proceed

• Enzymes work fastest at their ‘optimum temperature’ – in the human body, the optimum temperature is 37⁰C

• Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape -this is known as denaturation

• Substrates cannot fit into denatured enzymes as the shape of their active site has been lost

• Denaturation is irreversible - once enzymes are denatured they cannot regain their proper shape and activity will stop

Increasing the temperature from 0⁰C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction

• This means that low temperatures do not denature enzymes, they just make them work more slowly

Enzymes & pH

The optimum pH for most enzymes is 7 but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)

• If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed

• This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity

• Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop

Effect of pH on enzyme activity