3.1 RP

Question 1

Give examples of variables that could affect the rate of an enzyme-controlled reaction

Answer 1

• Enzyme concentration / volume
• Substrate concentration / volume
• Temperature of solution
• pH of solution
• Inhibitor concentration

Question 2

Describe how temperature can be controlled

Answer 2

• Use a thermostatically controlled water bath
• Monitor using a thermometer at regular intervals

Question 3

Describe how pH can be controlled

Answer 3

• Use a buffer solution
• Monitor using a pH meter at regular intervals

Question 4

Why were the enzyme & substrate solutions left in the water bath for 10 mins before mixing?

Answer 4

• So solutions equilibrate / reach the temperature of the water bath

Question 5

Describe how the rate of an enzyme-controlled reaction can be measured

Answer 5

• Measure time taken for reaction to reach a set point eg. concentration / volume / mass / colour of substrate or product
• Rate of reaction = 1 / time

• Measure concentration / volume / mass / colour of substrate or product at regular intervals throughout reaction
• Plot on a graph with time on the x axis and whatever is being measured on the y axis
• Draw a tangent at t = 0 (or any other time for rate at a particular point)
• Initial rate of reaction = change in y / change in x

Question 6

Explain why using a colorimeter to measure colour change is better than comparison to colour standards

Answer 6

• Not subjective
• More accurate

Question 7

Explain a procedure that could be used to stop the enzyme substrate reaction

Answer 7

• Boil / add strong acid / alkali → denature enzyme
• Put in ice → lower kinetic energy so no E-S complexes form
• Add high concentration of inhibitor → no E-S complexes form