Proteins · Paper 1 — Free Biology HL Practice Questions

A student adds catalase to equal volumes of the same concentration of hydrogen peroxide ($\text{H}_2\text{O}_2$) at 25°C and at 45°C. The initial rate of oxygen production is higher at 45°C, yet the total volume of oxygen collected after 10 minutes identical in both trials. Which of the following best explains why the initial rate is higher at 45°C?

A student investigates the effect of pH on the activity of pepsin by measuring amino acid concentration produced after 10 minutes at 37 °C. Each test tube contains identical concentrations of protein substrate and pepsin, buffered to a different pH. The results are shown below. pH — Amino acid concentration (mmol $\text{L}^{-1}$) 2 — 12 4 — 8 6 — 3 8 — 1 Which conclusion is best supported by these data?

Secondary structure in proteins (alpha-helices and beta-sheets) is stabilised primarily by hydrogen bonds between backbone carbonyl and amide groups. A scientist analyses the amino acid mixture produced in a Miller-Urey experiment and wants to determine whether these amino acids could form polypeptides with stable secondary structure. Which property of the amino acid mixture is most important to confirm?