Temperature / °C Time for film to clear / s 20 150 30 80 40 35 50 90 60 210 70 did not clear Fig. 4.1 Protease enzymes digest protein. A food scientist inve...

This question tests enzyme action, the effect of temperature including denaturation, and the biuret food test.

(a) When a protease digests protein the products are amino acids [1].

(b) The protease worked fastest at 40 °C [1] (the optimum temperature, where clearing time was shortest).

(c) Describe the change from 20 to 70 °C [3]: from 20 to 40 °C the rate increases (the clearing time falls) [1]; the rate is fastest at the optimum, 40 °C [1]; above 40 °C the rate decreases and the film takes longer to clear or does not clear [1]. Below the optimum, more heat gives molecules more kinetic energy and more successful collisions; above it, denaturation takes over.

(d) No clearing at 70 °C because the enzyme is denatured [1]; the high temperature permanently changes the shape of the active site [1]; so the substrate can no longer bind and no digestion of the protein occurs [1]. Denaturation is permanent, which is why the film never clears rather than just clearing slowly.

(e) The protease is useful in washing powder because it removes protein stains such as blood, egg or food [1], and it works without needing a high temperature, so washing at lower temperatures saves energy [1].

(f) The missing word is specific [1] - each enzyme acts on only one type of substrate because its active site fits only that substrate.

(g) The test for protein [3]: add biuret solution (sodium hydroxide followed by copper sulfate) [1]; mix [1]; a positive result turns the solution purple/violet (it stays blue if no protein is present) [1].