Enzyme

Biological catalyst that speed up the rate of reaction without being changed

Enzyme and substrate randomly move about in solution When an enzyme and it’s complementary substrate randomly collide forming enzyme substrate complex and a reaction occurs A product forms from the substrate when are released from the active site The enzyme is unchanged and will go catalyse further reaction

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

X-axis = temperature Y axis = rate of enzyme activity

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

X-axis = pH Y-axis = rate of enzyme activity