Sucrose phosphorylase is an enzyme found in some species of bacteria. One function of this enzyme is for the production of compounds that help to protect the cell from harmful osmotic changes in the external environment. Fig. 5.1 shows the reversible reaction that takes place within the bacterial cell. [Figure 5.1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

1. [1] fructose ; Ια or β
2. [2] any two from:
3. formation of enzyme-substrate complex / substrate fits into active site ;
4. A substrate binds to active site
5. (so) reactants held close together (e.g. for bond formation) ;
6. lowers, activation energy / energy of activation ; A Ea / Ae
7. can award annotated on a sketch
8. detail; e.g. transfer of electrons
9. strain on bonds
10. alternative pathway
11. holds substrate in a way that the bonds needed to be broken are exposed
12. [4] I ref. to denaturation, either mp2 or mp10 can be awarded
13. any four from:
14. immobilised
15. 1 higher optimum temperature ; AW e.g. peak/ max activity/ 100% activity;
16. 2 74/75/76°C, v, 56 / 57 / 58 / 59°C ;
17. A one correct value and calculation e.g. 17°C lower
18. 3 idea that greater range of pH with, higher activity / greater stability; AW
19. allow use of comparative data at one pH value to support if answer unclear
20. 4 idea that if pH changes, less effect on enzyme activity;
21. A resists changes in pH
22. 5 ref. to more active at, higher temperatures / temperatures above 68°C;
23. A more thermostable / less effect on enzyme at higher temperatures
24. A free enzyme not active above 70°C
25. allow use of comparative data at one temperature to support if answer unclear
26. 6 one advantage of immobilised; e.g. reusable
27. Ο less/no, contamination of product (by enzyme)
28. Ο easier, downstream processing / separation of enzyme from product
29. Ο longer shelf-life useful if enzyme, difficult to obtain A ref. to cost effective
30. Ο can use in continuous processes so more productive
31. Ο suggestion that (can carry out process at) lower pH (more acid conditions and) may be more effective against microorganisms
32. free enzyme
33. 7 higher activity, at lower temperatures / between 35°C to 68°C;
34. in context of a range, quoting one temperature not enough
35. 8 two temperatures, comparative values for both enzymes to support mp7 ;
36. 9 optimum temperature lower so cheaper maintaining that temperature ;
37. AW
38. A lower temperatures cost efficient to maintain and enzyme works well/AW
39. 10 (values of optimum) 74 / 75 / 76°C, v, 56 / 57 / 58 / 59°C ;
40. A calculation, e.g. 17°C lower
41. 11 lower optimum temperature still high enough to kill microorganisms;