RP1 -> the effect of ___ on the rate of an enzyme controlled reaction

variables that could affect the rate of an enzyme controlled reaction

● Enzyme concentration / volume

● Substrate concentration / volume

● Temperature of solution

● pH of solution

● Inhibitor concentration

Any one of these can be the independent variable and need to be varied (eg. by preparing a dilution series of varying concentrations). All others (except inhibitors) would be control variables so would need to be kept constant.

Describe how temperature can be controlled

● Use a thermostatically controlled water bath

● Monitor using a thermometer at regular intervals and add hot / cold water if temperature fluctuates

Describe how pH can be controlled.

• Use a buffer solution

• Monitor using a pH meter at regular intervals

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

So solutions equilibrate / reach the temperature of the water bath

Describe a control experiment.

● 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

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

● Measure time taken for reaction to reach a set point,

eg. concentration / volume / mass / colour of substrate or product

○ Rate of reaction = 1 / time; example units = s-1

● Measure concentration / volume / mass / colour of substrate or product at regular intervals (or using a continuous data logger) 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; example units = cm3 s-1

Describe how processed data can be presented as a graph

● Independent variable on x axis, rate of reaction on y axis, including units

● Linear number sequence on axis, appropriate scale (graph should cover at least half of grid)

● Plot coordinates accurately as crosses

● Join point to point with straight lines if cannot be certain of intermediate values OR draw a smooth curve but do not extrapolate

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

● 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

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

● Handling enzymes may cause an allergic reaction

● Avoid contact with skin by wearing gloves and eye protection

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

● 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

Explain why using a colorimeter to

measure colour change is better than

comparison to colour standards.

● Not subjective

● More accurate