Biology 9700 · AS & A Level · Structure of nucleic acids and replication of DNA
Structure of nucleic acids and replication of DNA — practice question
Catalase is an enzyme that speeds up the decomposition of hydrogen peroxide, a toxic waste product of metabolism. The reaction is $2\text{H}_2\text{O}_2 \xrightarrow{\text{catalase}} 2\text{H}_2\text{O} + \text{O}_2$. Fig. 3.1 presents the findings of an investigation into how hydrogen peroxide concentration affects the rate of the catalase-controlled reaction, both in the absence of inhibitors and in the presence of two different inhibitors.
(a)[1]
The inhibitors used in this investigation act by different mechanisms. Identify which of curves X, Y and Z correspond to: the reaction with the non-competitive inhibitor, the reaction with the competitive inhibitor, and the reaction with no inhibitor at all.
(b)[4]
Using Fig. 3.1, compare the maximum reaction rate, $V_{\max}$, and the Michaelis-Menten constant, $K_m$, for curves X, Y and Z.
(c)[4]
Describe how DNA is structured.
(d)[2]
Cells have mechanisms that repair DNA damage caused by hydrogen peroxide. Mistakes during repair can change the DNA structure. Research has examined the possible risks linked to foods and drinks containing hydrogen peroxide, because this compound may be regarded as a mutagen. Mutagens cause mutations. Explain why hydrogen peroxide can be considered a mutagen.
Worked solution & mark scheme
This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Correct matching of X (no inhibitor), Y (competitive inhibitor) and Z (non-competitive inhibitor)” …