A laboratory technician needs to estimate the concentration of pepsin in an unlabelled solution.
The technician tests two reference pepsin solutions at pH 2. The volume and concentration of substrate, temperature and total volume of the reaction mixture are kept the same. The time taken for the reaction to finish is recorded three times for each reference solution.
| Concentration of pepsin in %\%% | Time for reaction to finish in repeat 1 in s\mathrm{s}s | Time for reaction to finish in repeat 2 in s\mathrm{s}s | Time for reaction to finish in repeat 3 in s\mathrm{s}s |
|---|---|---|---|
| 0.5 | 90 | 100 | 110 |
| 1.0 | 45 | 50 | 55 |
The technician calculates rate using rate=1000mean time\text{rate} = \dfrac{1000}{\text{mean time}}rate=mean time1000.
Calculate the mean time and rate for each reference pepsin solution.
The technician tests the unlabelled sample using the same procedure and under the same conditions as the reference solutions. The unlabelled sample has a mean reaction time of 62.5 s.
Calculate its rate and use the reference results to suggest the concentration of pepsin in the sample.
184 exam-style questions on OCR GCSE Biology 1.2 What happens in cells (and what do cells need)?, covering 1.2.1 Structure of DNA, 1.2.2 Nucleotides and complementary bases, 1.2.3 Protein synthesis, 1.2.4 DNA structure and the proteins made, 1.2.5 Investigating enzymatic reactions, and 1.2.6 Mechanism of enzyme action. Each one has a worked solution and a mark scheme showing where the marks go.