Question

3 fig. 3.1 shows the apparatus used to investigate the effect of bile on the digestion of milk fat by lipase. the reaction mixture contained milk, the enzyme and an alkali. in experiment 1, bile was replaced by an equal volume of water. in each experiment, the ph was recorded at 2 minute intervals. in experiment 2, bile was added. (image of apparatus: ph electrode in reaction mixture, connected to ph meter) fig. 3.1 the results are shown in table 3.2. table 3.2 | time (in minutes) | ph - experiment 1 (bile not added) | ph - experiment 2 (bile added) | |---|---|---| | 0 | 9.0 | 9.0 | | 2 | 9.0 | 8.7 | | 4 | 9.0 | 8.3 | | 6 | 8.7 | 8.0 | | 8 | 8.4 | 7.5 | (a) (i) use the lock and key hypothesis to explain how lipase specifically catalyses the digestion of fat molecules. 3

Explanation:

The 'lock and key' hypothesis states that an enzyme (lipase here) has an active site with a specific shape, like a lock. Fat molecules (substrate) have a complementary shape, like a key. Lipase's active site fits only fat molecules, forming an enzyme - substrate complex. This complex formation lowers the activation energy for fat digestion, and the enzyme catalyzes the breakdown of fat into products (e.g., fatty acids and glycerol), after which the enzyme is released to act on more fat molecules.

Answer:

According to the 'lock and key' hypothesis: 1. Lipase has an active site with a specific three - dimensional shape. 2. Fat molecules (substrate) have a complementary shape to the active site of lipase, similar to a key fitting into a lock. 3. Only fat molecules can fit into the active site of lipase to form an enzyme - substrate complex. 4. Once the complex is formed, lipase catalyzes the breakdown of fat molecules (e.g., into fatty acids and glycerol), and then the enzyme is released to bind with more fat molecules.