Biology 9700 · AS & A Level
Mode of action of enzymes
100 practice questions on Mode of action of enzymes, with worked solutions and instant marking.
Which statement accurately describes how competitive enzyme inhibitors act?
Feb/March 2016
What does the enzyme DNA polymerase produce in a cell?
Feb/March 2016
An enzyme was mixed with a slight excess of its substrate. Every variable was held constant. A student had to draw a graph showing how the concentration of the enzyme-substrate complex varies with time. Which graph represents this accurately?
Feb/March 2017
The diagram illustrates an enzyme, the substrate and an enzyme/substrate complex. Which statement explains why the substrate can enter the enzyme's active site?
Feb/March 2018
Which protein-structure levels can determine an enzyme’s specificity?
Feb/March 2019
The diagram shows the reversible binding between the active site of an enzyme and the inhibitors X and Y. Which row correctly names the type of inhibition shown by inhibitor X and inhibitor Y?
Feb/March 2019
Antibiotics fall into two main categories: broad spectrum and narrow spectrum. Broad spectrum antibiotics act on a broad range of bacteria, whereas narrow spectrum antibiotics act on particular kinds of bacteria. Which uses of antibiotics could lead to antibiotic-resistant bacteria?
Feb/March 2021
Which statement gives an example of an extracellular enzyme?
Feb/March 2023
Which row gives the correct description of enzymes that catalyse reactions according to the lock-and-key hypothesis?
Feb/March 2023
A scientist studied how quickly hydrogen peroxide decomposed. Four experiments were done using different mixtures: substrate only, substrate + enzyme, substrate + enzyme + competitive inhibitor, substrate + enzyme + non-competitive inhibitor. The results are shown in the graph sketch. Which row gives the correct lines for two of the experimental mixtures?
Feb/March 2023
A student carried out an investigation into the hydrolysis of lipid in high-fat milk, using the enzyme lipase. • $1\ \text{cm}^3$ of enzyme solution was added to $10\ \text{cm}^3$ of high-fat milk. • The temperature was maintained at a constant value. • The pH of the reaction mixture was measured at time $0$ minutes and then at 1-minute intervals for $20$ minutes. Which statements describe the results that would be expected for this investigation?
Feb/March 2024
Catalase is an enzyme which decomposes hydrogen peroxide into water and oxygen. Catalase was introduced into a hydrogen peroxide solution, and the oxygen given off was gathered in a gas syringe. The overall volume of oxygen produced from the beginning of the reaction was measured every 10 seconds for 1 minute. The results are displayed in the table. What conclusion can be drawn from these results?
Feb/March 2025
Succinic dehydrogenase is an enzyme that catalyses the conversion of succinate into fumarate during aerobic respiration. Malonate is a reversible inhibitor of succinic dehydrogenase. By binding to the enzyme’s active site, malonate lowers the enzyme’s activity. Malonate and succinate are unable to bind to the active site at the same time. Which statement explains the effect of malonate on the activity of succinic dehydrogenase?
Feb/March 2025
Lysozyme, which is released by tear glands, builds up as deposits on contact lenses. Which ingredient would be suitable in a cleaner for contact lenses to remove these deposits?
May/June 2010
The enzyme lysozyme released by tear glands builds up on contact lenses. Which ingredient would be effective in a contact lens cleaner for removing these deposits?
May/June 2010
The graph illustrates the activation energy for an enzyme-catalysed reaction and for the same reaction when no catalyst is present. Which of the following indicates the activation energy of the reaction without a catalyst?
May/June 2011
Which of the following statements are true for every enzyme?
May/June 2011
What is synthesised by the enzyme RNA polymerase?
May/June 2011
Some inhibitors of enzyme reactions attach to the enzyme/substrate complex. Which statements about this type of inhibition are correct?
May/June 2011
Which protein-structure levels are able to determine an enzyme’s specificity?
May/June 2011
The graph illustrates how a reaction proceeds with and without an enzyme. What is the activation energy of the reaction when the enzyme is present?
May/June 2012
Which graph shows the pattern of change in the concentration of a substrate and its product in the same enzyme-catalysed reaction?
May/June 2012
Glucose in urine may be identified by means of a biochemical test. If the end of a test strip coated with the enzyme glucose oxidase is placed into urine, the appearance of a blue colour shows that glucose is present. This test is dependable and can be done at home by people with diabetes. Which characteristic of the enzyme makes this test so dependable?
May/June 2012
The graph illustrates the course of a reaction with and without an enzyme present. What is the activation energy for the reaction when the enzyme is present?
May/June 2012
Which processes are needed to make nitrogen in dead plant material available to growing plants?
May/June 2013
Two pairs of students each recorded how many oxygen bubbles were released in 1 minute while investigating the effect of catalase from plant tissue on hydrogen peroxide. Each pair carried out the experiment five times and then worked out the mean number of bubbles per minute. Which pair has correctly worked out the mean?
May/June 2013
The statements concern enzymes. Which of these statements is true for every enzyme?
May/June 2014
A tropical grass has been discovered to contain an unusual enzyme. It speeds up the hydrolysis of the fungal polysaccharide chitin into amino sugars. It also reduces the activity of an enzyme in locust guts that catalyses the digestion of amylose. Which description best fits the actions of this unusual enzyme?
May/June 2014
The drug ritonavir is sometimes used to treat HIV/AIDS. Ritonavir is made up of three amino acids and acts as a competitive inhibitor of HIV protease. Which of the following statements about ritonavir are correct?
May/June 2014
Which statements show some functions of enzymes? 1 speed up the breakdown of larger molecules into smaller ones 2 reduce the activation energy needed to begin a reaction 3 raise the number of collisions between molecules 4 provide the activation energy needed to begin a reaction
May/June 2014
What occurs once carbonic anhydrase has catalysed a reaction involved in the transport of carbon dioxide?
May/June 2015
Which levels of protein structure are invariably involved when competitive and non-competitive inhibitors attach to enzymes?
May/June 2015
What is necessary for DNA to be transcribed?
May/June 2015
Influenza virus contains an enzyme named neuraminidase, which breaks down glycoproteins in the membrane of the cell that the virus will infect. The glycoprotein binds to the active site of neuraminidase by induced fit. Which statements concerning the induced fit hypothesis of enzyme action are correct?
May/June 2016
Which row concerning competitive inhibitors of enzymes is correct?
May/June 2016
Which statement applies only to the induced fit theory of enzyme action?
May/June 2016
What decides the specificity of an enzyme?
May/June 2017
The statements below concern enzymes. Which of these statements are correct according to the induced fit hypothesis?
May/June 2017
In what way is the Michaelis-Menten constant ($K_m$) used?
May/June 2017
The graph illustrates energy changes during a chemical reaction. What is the activation energy when an enzyme is present?
May/June 2017
Scientists have developed a nucleic acid (HNA) whose sugar contains the same number of carbon atoms as glucose rather than deoxyribose. Even though HNA can store genetic information, naturally occurring DNA polymerase is unable to replicate HNA. Which statements might account for the fact that naturally occurring DNA polymerase cannot replicate HNA?
May/June 2017
A student carried out an investigation into the hydrolysis of the lipid present in high-fat milk, using the enzyme lipase. • $1\,\text{cm}^3$ of enzyme solution was added to $10\,\text{cm}^3$ of high-fat milk. • The temperature was held constant. • The pH of the reaction mixture was measured at time $0$ minutes and then every minute for $20$ minutes. Which statements are supported by the results of the investigation?
May/June 2018
Catechol is a chemical present in several fruits. The enzyme catechol oxidase can oxidise catechol into a quinone. Parahydroxybenzoic acid (PHBA), which has a structure similar to catechol, inhibits catechol oxidase. Phenylthiourea (PTU) also inhibits catechol oxidase by binding to a copper atom in the enzyme. In what way do both of these inhibitors lower enzyme activity?
May/June 2018
What effect does an enzyme have in an enzyme-catalysed reaction?
May/June 2018
How is the Michaelis-Menten constant, $K_m$, for an enzyme defined?
May/June 2019
A solution of amylase was mixed with a starch suspension. After 30 seconds, three samples of the mixture were tested using iodine solution, Benedict’s solution and biuret reagent. Which results would be expected?
May/June 2019
An unchanged volume of the enzyme catalase was mixed with an unchanged volume of hydrogen peroxide solution. The diagram illustrates how the concentration of product altered during the reaction. What accounts for the shape of this graph?
May/June 2019
A set volume and concentration of substrate and enzyme were combined. Every other variable was held constant. The enzyme-catalysed reaction was allowed to continue until it had finished. Which graph shows the way the rate of reaction changes over time?
May/June 2019
Which levels of protein structure would always be altered if an enzyme acts by the induced fit hypothesis?
May/June 2019
The enzyme β-galactosidase is able to catalyse the hydrolysis of four substrates, A, B, C and D, which have similar structures. Each substrate has a different $K_m$ value. Which substrate does β-galactosidase have the lowest affinity for?
May/June 2019
In what way does penicillin affect bacteria?
May/June 2019
A solution of amylase was added to a suspension of starch. The mixture was stirred and maintained at $40^\circ\text{C}$ for 45 minutes. Samples were then tested using different reagents. What set of results would be expected?
May/June 2019
Protease enzymes occur in numerous places both inside and outside cells. Four such locations are given. Which of these locations are sites of intracellular hydrolysis?
May/June 2020
An enzyme has been altered for industrial use. Compared with the unmodified enzyme, it has a lower Michaelis-Menten constant ($K_m$). What is true about the modified enzyme?
May/June 2020
Scientists have produced a nucleic acid, HNA, whose sugar has the same number of carbon atoms as glucose rather than deoxyribose. Even though HNA can store genetic information, naturally occurring DNA polymerase cannot copy HNA. Which statements could account for naturally occurring DNA polymerase being unable to copy HNA?
May/June 2020
The enzyme carbonic anhydrase catalyses the reaction: $\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{HCO}_3^- + \text{H}^+$ Which statements describe the function of the enzyme carbonic anhydrase?
May/June 2020
Which graph correctly displays the activation energy for a reaction when an enzyme has been added?
May/June 2021
The figure illustrates sucrose and sucralose. The enzyme sucrase hydrolyses sucrose but is unable to hydrolyse sucralose. Four students were asked to propose reasons why sucrase can hydrolyse sucrose but not sucralose. Three of the students made correct proposals. Which proposal cannot be correct?
May/June 2021
The diagram displays the energy levels involved in an enzyme-catalysed reaction. Substrate molecules X and Y join together to form product Z. Which arrow indicates the decrease in activation energy caused by the enzyme?
May/June 2021
Which main reaction takes place in the blood capillaries at the gas-exchange surface of a human lung?
May/June 2021
The enzyme $\beta$-galactosidase is able to catalyse the hydrolysis of four substrates that have similar structures. Each substrate produces a different $K_m$ value. Which substrate does $\beta$-galactosidase have the greatest affinity for?
May/June 2021
A student carried out colorimetry to follow the hydrolysis of a protein by a protease enzyme. Biuret solution was used by the student to find the protein concentration in the hydrolysis reaction. The student then made a calibration curve from known protein concentrations. Which diagram shows the calibration curve?
May/June 2022
To investigate how the rate of an enzyme-controlled reaction changes as substrate concentration increases, a student carried out an experiment. The student repeated the investigation after introducing a fixed amount of a reversible competitive inhibitor. Which row shows the effect of a reversible competitive inhibitor on enzyme activity?
May/June 2022
Which statement about the Michaelis-Menten constant ($K_m$) is correct for an enzyme that has a low affinity for its substrate?
May/June 2022
Rifampicin is an antibiotic that is used in the treatment of tuberculosis. Its action is to inhibit RNA polymerase in bacteria. Which processes are directly affected by this antibiotic? 1 DNA replication 2 enzyme synthesis 3 ATP synthesis
May/June 2022
RNA polymerase and peptidyl transferase are both enzymes that take part in protein synthesis. Which statements describe similarities between these two enzymes?
May/June 2022
Which part of the graph indicates the activation energy for an enzyme-catalysed reaction?
May/June 2023
CYP3A4 is a key enzyme in the human digestive system, where it is required to break down a variety of toxins. The activity of CYP3A4 has been found to be lowered by compounds known as furanocoumarins. Furanocoumarins occur in some fruits, so harmful concentrations of toxins may build up in the human digestive system when fruits containing furanocoumarins are consumed. From the information given, what can be concluded about molecules of the enzyme CYP3A4?
May/June 2023
A fixed volume and concentration of substrate and enzyme were combined. Every other variable was kept unchanged. The enzyme-catalysed reaction was allowed to continue until it had finished. Which graph shows how the rate of reaction changes with time?
May/June 2023
The final product of a metabolic pathway may function as a competitive inhibitor. This is known as end-product inhibition, and it enables a cell to regulate a metabolic pathway. The diagram illustrates a metabolic pathway in which the end-product could inhibit enzyme W. What effect would there be if, rather than enzyme W, the end-product inhibited enzyme Z?
May/June 2023
Which of the following statements about the Michaelis-Menten constant ($K_m$) are correct?
May/June 2024
The diagram illustrates a straightforward metabolic pathway. $W \rightarrow X \rightarrow Y \rightarrow Z$ The letters W, X, Y and Z stand for four different substances. At every stage in the diagram, the substrate is changed in a chemical reaction that is catalysed by an enzyme. This reaction forms the next substance in the pathway. Which statements accurately describe the enzymes involved in this metabolic pathway?
May/June 2024
Which row shows the anticipated effect on $V_{\max}$ and $K_{m}$ when a competitive reversible inhibitor is introduced into an enzyme-catalysed reaction?
May/June 2024
Which bond formation is catalysed by DNA polymerase?
May/June 2024
The diagram illustrates naturally occurring D-glucose and a glucose form that may be made in a laboratory, called L-glucose. The enzyme glucose oxidase catalyses the oxidation of D-glucose. The enzyme is unable to catalyse the oxidation of L-glucose. Which statement about L-glucose accounts for this?
May/June 2024
The diagram shows various molecules in a solution. Which statement could explain what happens when some of the molecules are combined?
May/June 2024
Which feature of enzyme activity can be compared using the Michaelis-Menten constant?
May/June 2024
The number of substrate molecules that one enzyme molecule can turn into product in 1 second is known as the turnover number. It is measured when the conditions are optimum for that particular enzyme-catalysed reaction. Catalase: 2 800 000 Carbonic anhydrase: 600 000 Phosphatase: 971 Protease: 100 By what factor is catalase faster than phosphatase in converting substrate into product?
May/June 2024
Which of the following statements about an enzyme’s mode of action are correct?
May/June 2025
Prokaryotes and eukaryotes both make extracellular enzymes. In the external surroundings of some prokaryotes, extracellular digestive enzymes are present. When phagocytosis occurs in eukaryotic cells, hydrolytic enzymes digest some prokaryotes. Which row indicates the places where extracellular enzymes are made?
May/June 2025
Amylase breaks down starch molecules. Which substance will keep the same number of molecules throughout this reaction?
May/June 2025
Which graph accurately shows $K_m$ and $V_{max}$?
May/June 2025
Which statement could describe how resistance to penicillin develops in bacteria?
May/June 2025
Which reaction does carbonic anhydrase catalyse?
May/June 2025
Which molecule is needed for this reaction to take place? $\text{C}_{12}\text{H}_{22}\text{O}_{11} + \text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + \text{C}_6\text{H}_{12}\text{O}_6$
May/June 2025
The graph illustrates the progression of an enzyme-catalysed reaction at $30\degree\text{C}$. What is true at time $X$?
Oct/Nov 2010
The equation represents a reversible reaction. $\text{sucrose} + \text{water} \rightleftharpoons \text{glucose} + \text{fructose}$ (In the presence of the enzyme sucrase) For this reaction, which molecule has an active site, and what kinds of reaction take place at 1 and 2?
Oct/Nov 2010
Which levels of protein structure are invariably involved when competitive and non-competitive inhibitors attach to enzymes?
Oct/Nov 2010
S and T are end products of a biochemical pathway. Each stage in the pathway is catalysed by a different enzyme, which is encoded by specific genes. What may happen to the pathway if a mutation in gene 3 results in an inactive enzyme?
Oct/Nov 2010
The equation represents a reversible reaction. $\text{sucrose} + \text{water} \; \rightleftharpoons \; \text{glucose} + \text{fructose}$ (This occurs in the presence of sucrase.) For this reaction, which molecule has an active site, and what kind of reactions take place at 1 and 2?
Oct/Nov 2010
The graph illustrates the progress of an enzyme-catalysed reaction at $30\,^{\circ}\text{C}$. What is true at time X?
Oct/Nov 2010
The graph illustrates how an enzyme affects a reaction. Which option identifies X, Y and Z?
Oct/Nov 2011
The graph illustrates the effect of an enzyme on a reaction. Which combination identifies X, Y and Z?
Oct/Nov 2011
What effect does an enzyme have in an enzyme-catalysed reaction?
Oct/Nov 2012
What role do enzymes play in metabolism?
Oct/Nov 2012
The diagrams illustrate the point at which an inhibitor binds to an enzyme and whether the binding is permanent or temporary. Which diagrams show a non-competitive inhibitor?
Oct/Nov 2012
Which of the following statements about competitive inhibitors of enzyme action are correct? 1 Raising the concentration of the enzyme’s substrate will lessen their effect. 2 They attach to an enzyme at its active site. 3 They lower the activation energy needed for a reaction to occur. 4 They decrease the maximum rate of reaction.
Oct/Nov 2013
What does the enzyme DNA polymerase make in a cell?
Oct/Nov 2013
The enzyme lysozyme, released by tear glands, builds up on contact lenses. Which ingredient would be suitable in a cleaner for contact lenses to remove these deposits?
Oct/Nov 2013
Which statement about competitive inhibitors of enzymes is correct?
Oct/Nov 2013