Enzymes & Temperature (Cambridge International IGCSE Biology)

Enzymes & temperature: Extended

Spec point — 5.1.4 · Explain the effect of changes in temperature on enzyme activity in terms of kinetic energy, shape and fit, frequency of effective collisions and denaturation

Extended Tier Only

• 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 37 °C
• Heating to high temperatures (beyond the optimum) breaks the bonds that hold the enzyme's structure together, causing it to lose its shape
• This changes the shape of the active site so it's no longer complementary to the substrate, and the enzyme is denatured
• 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

Effect of temperature on enzyme activity

• Increasing the temperature from 0 °C 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

Graph showing the effect of temperature on the rate of enzyme activity