Required practical 1

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 and add hot / cold water if temperature fluctuates

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 a control experiment.

Answer 5

● Use denatured enzymes (eg. by boiling)
● Everything else same as experiment, eg. same conc. /volume of substrate (at start) and enzyme, same type / volume of buffer solution, same temperature

Question 6

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

Answer 6

● Measure time taken for reaction to reach a set point, eg. concentration / volume / mass / colour of substrate or product
● 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 7

Suggest a safety risk and explain how
to reduce this risk.

Answer 7

● Handling enzymes may cause an allergic reaction
● Avoid contact with skin by wearing gloves and eye protection

Question 8

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

Answer 8

● Not subjective
● More accurate

Question 9

Explain a procedure that could be
used to stop each reaction.

Answer 9

● 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

Question 10

Explain why the rate of reaction decreases over time throughout each experiment

Answer 10

● Initial rate is highest as substrate concentration not limiting / many E-S complexes form
● Reaction slows as substrate used up and often stops as there is no substrate left