core practical 1: investigate a factor affecting the initial rate of reaction

what is the method for this experiment?

1. Dilute stock solution of trypsin with distilled water to produce solutions with concentrations of 0.2%, 0.4%, 0.6% and 0.8%

2. Make a control by adding 2cm3 of tryspsin solution and 2cm3 of distilled water - use this to set the colorimeter absorbance to zero

3. to another cuvette, add 2cm3 of milk suspension and 2cm3 of stock trypsin solution. Mix, place in the colorimeter and measure absorbance at 15 second intervals for 5 minutes.

4. Rinse the cuvette with distilled water. Repeat step 3 with all concentrations of trypsin solution.

independent variable

tryspin concentration

dependent variable

rate of reaction in absorbance units

why do you measure the initial rate of reaction?

• reaction is rapid and milkv(substrate) conc quickly declines

• the only time when substrate concentration is known

• allows for comparisons to be made at the start of the reaction - as the controlled variable of substrate conc is the same for all levels of the independent reaction.

precautions that need to be taken when using cuvettes

• add the same volume of solution to the cuvette

• make sure to callibrate before each reading

• hold cuvette by the top to prevent smudges/finger prints on the cuvette

what will this experiment show?

• as trypsin concentration increases, the rate of reaction increases. (calculated by drawing a tangent)

• This is because as conc of enzymes increases, the availability of active sites increase so more enzyme-substrate complexes form.

control variables

temperature, pH, volume of enzyme and milk solutions.

how can you increase the accuracy of this experiment?

dataloggers to automatically take readings at certain time intervals