3. Enzymes

Question 1

Suggest reasons for the higher activity of immobilised sucrase over the range of pH between 5.5 and 8.0 compared with sucrase free in solution. [4m]

Answer 1

• immobilisation has stabilising effect
• OH- ions do not penetrate the alginate beads
• shape of ACTIVE SITE of immobilised enzyme is less distorted
• fewer bonds (hydrogen/ionic) within immobilised enzyme break

Question 2

Suggest how the difference in one amino acid is responsible for the lower activity of catalase Q compared with catalase P. [2m]

Answer 2

• amino acid is part of the ACTIVE SITE
• different R group gives different properties
• different tertiary structure
• different interactions between polypeptides in catalase

Question 3

Suggest why product inhibition is useful when lactase is acting as an intracellular enzyme, but can be a disadvantage when extracted lactase is used free in solution for the production of lactose-free milk. [2m]

Answer 3

Pro: control/effective metabolism
eg. if enough glucose present, there is no need for breakdown of lactose; this is to avoid osmotic problems

Con: reduced productivity, as enzyme needs to be remained active for production of lactose-free milk

Question 4

Suggest how using immobilised lactase helps to reduce the problem of product inhibition. [2m]

Answer 4

• products and enzyme do not mix (are kept separated)

- product removed immediately

Question 5

Explain how the addition of a competitive inhibitor results in the same value for Vmax but a higher value for Km. [4m]

Answer 5

• competitive inhibitor competes with substrate for ACTIVE SITE
• fewer ESCs form
• lower reaction rate at low substrate concentration
• at high substrate conc. inhibitor has no effect (substrate outcompetes inhibitor)
• Vmax is the same as it is determined by enzyme conc. - active sites are saturated
• intercept to curve gives higher value for Km

Question 6

7 advantages of using small (alginate) beads rather than large beads

Answer 6

1. pack more beads into the column
2. slows the passage of milk through the column
3. more time for enzyme to be exposed to substrate
4. small beads have a larger SA:V ratio
5. rate of reaction will be faster
6. faster rate of diffusion of substrate
7. will take less time to collect results at each temperature

Question 7

6 steps to investigate the progress of an enzyme-catalysed reaction experimentally

Answer 7

1. constant variables - constant pH / temperature
2. take samples at regular time intervals
3. determine substrate concentration / product concentration
4. plot graph of dependent variable (y-axis) against time (x-axis)
5. measure rate of disappearance or substrate OR rate of appearance of product
6. determine initial rate