Using the lock and key hypothesis, explain the action of sucrase on sucrose.

Sucrase was the lock and sucrose was the key [0.5].

Sucrose has a shape complementary to the active site of sucrase [0.5] and thus binds to it to form the enzyme-substrate complex [0.5].

Sucrose is then broken down [0.5] to form the products fructose and glucose [0.5]. The products are then released and sucrase remains unchanged and is ready for the next reaction [0.5].

The optimum temperature of sucrase is 55 ^oC. What would happen if a mixture of sucrase and sucrose was placed in a water bath of 80 ^oC.

Sucrase would be denatured [1]. The active site would be altered [0.5]. Sucrose is not complementary to shape of active site [0.5]. Sucrose can no longer bind to it [0.5] and is thus not broken down [0.5].

Explain how reducing sugar may have appeared in the sample from A.

Starch was broken down by salivary amylase in the mouth to form maltose.

Maltose is a reducing sugar.

The juice from duct X is boiled for 10 minutes and then mixed with peanut oil and water. The mixture is shaken vigorously for a while. State and explain what you expect to observe.

A white emulsion is formed. [1] The juice from duct X contains bile which emulsifies fats into smaller fat droplets.[1] Since bile is not an enzyme, boiling has no effect on its activity. [1]