Question 1
What property allows a small amount of enzyme to catalyse many reactions in a cell?
A.
The enzyme is regenerated after product formation.
B.
The enzyme becomes part of each product molecule.
C.
The enzyme supplies the energy released by the products.
D.
The enzyme changes the final energy of the products.
Question 2
A reaction joins many glucose molecules to form glycogen and releases water. What classification best describes this reaction?
A.
Catabolic condensation
B.
Anabolic condensation
C.
Anabolic hydrolysis
D.
Catabolic hydrolysis
Question 3
An enzyme is tested at increasing substrate concentrations while temperature, pH and enzyme concentration are kept constant. The rate rises rapidly at first and then levels off. What explains the levelling off?
A.
Most active sites are occupied at any moment.
B.
The enzyme molecules have all been used up as reactants.
C.
Substrate molecules have stopped moving randomly.
D.
The pH has moved away from the enzyme optimum.
Question 4
Catalase activity is measured by collecting oxygen from hydrogen peroxide. A student collects of oxygen in . What is the reaction rate?
A.
B.
C.
D.
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Question 5
What row correctly classifies examples of enzyme-catalysed reactions by location?
A.
Krebs cycle: extracellular; glycolysis: extracellular
B.
Glycolysis: extracellular; chemical digestion in the gut: intracellular
C.
Glycolysis: intracellular; chemical digestion in the gut: extracellular
D.
Chemical digestion in the gut: intracellular; Krebs cycle: extracellular
Question 6
A cell controls a metabolic pathway by changing the amount of one enzyme that catalyses an early step in the pathway.
Define enzyme.
[1]
Explain how enzyme specificity allows control of metabolism.
[2]
Question 7
Metabolic reactions can be classified as anabolic or catabolic.
State whether protein synthesis is anabolic or catabolic.
[1]
Distinguish between anabolic and catabolic reactions.
[2]
State one example of a catabolic reaction in humans.
[1]
Question 8
Enzyme-catalysed reactions can occur inside cells or outside the cells that secrete the enzymes.
Distinguish between intracellular and extracellular enzyme-catalysed reactions, using examples.
[2]
Explain one advantage of extracellular digestion.
[1]
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Question 9
The diagram shows an energy profile for the same reaction with and without an enzyme. What change is caused by the enzyme?
A.
It lowers the product energy level and makes the reaction irreversible.
B.
It removes the transition state so that no bonds need to break.
C.
It lowers the activation energy but leaves the overall energy change unchanged.
D.
It raises the activation energy and increases the product energy level.
Question 10
The best diagram of induced-fit binding in an enzyme-catalysed reaction is shown in which option?
A.
B.
C.
D.
Question 11
The diagram that best represents a cyclical metabolic pathway is shown in which option?
A.
B.
C.
D.
Question 12
A reversible inhibitor binds to a site on an enzyme that is not the active site. The active site changes shape and catalysis is reduced. What type of inhibition is described?
A.
Competitive inhibition
B.
Mechanism-based inhibition
C.
Non-competitive inhibition
D.
Substrate-level inhibition
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Question 13
In the pathway producing isoleucine, high isoleucine concentration regulates the pathway by acting on threonine deaminase. What is the mechanism?
A.
Isoleucine binds to the final product and converts it back into threonine.
B.
Threonine binds to isoleucine and prevents it from leaving the pathway.
C.
Isoleucine binds allosterically to the first enzyme, reducing entry of threonine into the pathway.
D.
Threonine deaminase permanently destroys isoleucine when its concentration becomes high.
Question 14
Penicillin inhibits bacterial transpeptidase by mechanism-based inhibition. What change could confer resistance to penicillin?
A.
A transpeptidase active site that binds penicillin more tightly
B.
An altered transpeptidase active site that binds penicillin less effectively
C.
A loss of all peptidoglycan strands from the bacterial cell wall
D.
A transpeptidase that converts penicillin into a normal cell wall monomer
Question 15
The diagram shows a substrate binding to the active site of an enzyme.
State why the overall three-dimensional structure of the enzyme is important for catalysis.
[1]
Explain induced-fit binding in enzyme catalysis.
[3]
Question 16
The graph shows the effect of substrate concentration on the rate of an enzyme-catalysed reaction when enzyme concentration is constant.
Describe the relationship shown in the graph.
[2]
Explain the plateau in the graph.
[2]
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Question 17
Enzyme activity is affected by temperature and pH.
State the effect of increasing temperature on enzyme activity below the optimum temperature.
[1]
Explain why enzyme activity decreases above the optimum temperature.
[2]
Outline why different enzymes can have different optimum pH values.
[1]
Question 18
Small mammals increase their metabolic rate in cold conditions.
Explain why metabolic reactions generate heat.
[2]
State how this heat production is useful to mammals and birds.
[1]
Question 19
The diagram represents two types of metabolic pathway.
State the feature that makes a pathway cyclical.
[1]
Compare glycolysis and the Krebs cycle as metabolic pathways.
[2]
Suggest why regeneration of an intermediate is useful in a cyclical pathway.
[1]
Question 20
Catalase catalyses the decomposition of hydrogen peroxide. In an investigation, equal volumes of catalase extract were added to hydrogen peroxide solutions at the same temperature and pH. The oxygen produced was collected in a gas syringe.
Calculate the initial rate of oxygen production using the tangent shown on the graph.
[2]
Describe the change in rate during the reaction.
[1]
Suggest why the reaction rate changes in this way.
[1]
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Question 21
A student measured the rate of an enzyme-catalysed reaction at different substrate concentrations. Enzyme concentration, temperature and pH were kept constant.
Describe the relationship between substrate concentration and reaction rate shown in the graph.
[2]
Suggest why increasing substrate concentration has little effect in the plateau region.
[1]
State one control variable that should be kept constant in this investigation, other than enzyme concentration.
[1]
Question 22
The table summarizes enzyme-catalysed reactions in three metabolic processes.
Metabolic process | Example enzyme-catalysed reaction | Where the enzymes act |
|---|---|---|
Glycolysis | glucose is converted to pyruvate | cytoplasm of cells |
Chemical digestion in the gut | food macromolecules are hydrolysed to smaller molecules | gut lumen (outside the secreting cells) |
Krebs cycle | acetyl-CoA is broken down to carbon dioxide | mitochondrial matrix of cells |
Identify the process in the table that uses extracellular enzymes.
[1]
Compare the locations of the enzymes in glycolysis and chemical digestion in the gut.
[2]
Suggest why extracellular digestion is needed before many food molecules can be absorbed.
[1]
Question 23
An enzyme is tested with no inhibitor, with a fixed concentration of a competitive inhibitor, and with a fixed concentration of a non-competitive inhibitor. Substrate concentration is then increased to a very high value. What outcome is expected?
A.
Both inhibitor curves approach the same lower maximum rate because both inhibitors bind allosteric sites.
B.
The competitive inhibitor curve can approach the uninhibited maximum rate, but the non-competitive inhibitor curve remains lower.
C.
Neither inhibitor curve changes because substrate concentration does not affect enzyme activity.
D.
The non-competitive inhibitor curve approaches the uninhibited maximum rate, but the competitive inhibitor curve remains lower.
Question 24
Catalase catalyses the decomposition of hydrogen peroxide. In an investigation, of oxygen was collected in the first of the reaction.
Calculate the mean rate of oxygen production during the first .
[1]
State one variable, other than hydrogen peroxide concentration, that should be controlled in this investigation.
[1]
Explain how enzymes increase reaction rate by affecting activation energy.
[2]
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Question 25
A reversible inhibitor binds to an enzyme at a site separate from the active site.
Define allosteric site.
[1]
Explain how a reversible non-competitive inhibitor reduces enzyme activity.
[3]
Question 26
The graph shows enzyme activity at increasing substrate concentration with no inhibitor, with a competitive inhibitor and with a non-competitive inhibitor.
Explain how statins act as competitive inhibitors.
[2]
Distinguish between the effects of competitive and non-competitive inhibition when substrate concentration is increased.
[2]
Question 27
The effect of pH on the activity of two digestive enzymes was investigated using equal enzyme concentrations and equal substrate concentrations.
State the optimum pH for amylase in this investigation.
[1]
Compare the effect of pH on the activities of pepsin and amylase.
[2]
Explain why amylase activity is low at extreme pH values.
[1]
Question 28
The diagram shows a model of induced-fit binding during an enzyme-catalysed reaction.
Identify the labelled region where catalysis occurs.
[1]
Describe the evidence in the diagram that the model represents induced fit rather than a rigid lock-and-key model.
[1]
Explain how induced-fit binding can increase the rate of product formation.
[2]
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Question 29
The energy changes in a chemical reaction are shown with and without an enzyme.
Using the graph, state the effect of the enzyme on activation energy.
[1]
State the effect of the enzyme on the overall energy difference between substrates and products.
[1]
Explain why lowering activation energy increases reaction rate in cells.
[2]
Question 30
A small mammal was exposed to decreasing environmental temperatures. Its oxygen consumption and body temperature were monitored. Oxygen consumption was used as an indicator of metabolic rate.
Environmental temperature / | Oxygen consumption / mL | Body temperature / |
|---|---|---|
35 | 1.2 | 37.0 |
30 | 1.2 | 37.0 |
25 | 1.2 | 37.0 |
20 | 1.8 | 37.0 |
15 | 2.6 | 37.0 |
10 | 3.8 | 37.0 |
5 | 5.0 | 37.0 |
Describe the change in metabolic rate as environmental temperature decreases below the thermoneutral range.
[1]
Explain why increased metabolic activity can help maintain body temperature.
[2]
Suggest one mechanism that could increase metabolic heat production in the mammal.
[1]
Question 31
The diagrams show simplified representations of three metabolic pathways.
Identify the pathway that represents glycolysis.
[1]
Distinguish between a linear pathway and a cyclical pathway using evidence from the diagrams.
[2]
State one cyclical pathway shown that occurs in metabolism.
[1]
Question 32
Two examples of enzyme regulation or inhibition are feedback inhibition in isoleucine synthesis and inhibition of bacterial transpeptidase by penicillin.
Explain feedback inhibition in the pathway that produces isoleucine.
[2]
Explain why penicillin is described as a mechanism-based inhibitor and how a changed transpeptidase can confer resistance.
[2]
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Question 33
A simplified metabolic network in a liver cell is shown. The arrows represent enzyme-catalysed reactions. Some reactions require ATP and release water; others use water and release smaller molecules.
Deduce one anabolic reaction shown in the network.
[1]
Deduce one catabolic reaction shown in the network.
[1]
Explain one difference between the anabolic and catabolic reactions shown.
[2]
Suggest why many different enzymes are needed in the network.
[1]
Question 34
An enzyme was tested at different substrate concentrations with no inhibitor, with inhibitor X and with inhibitor Y. The same enzyme concentration was used in all trials.
Identify which inhibitor is most likely to be competitive.
[1]
Explain the effect of increasing substrate concentration on competitive inhibition.
[2]
Explain why inhibitor Y is unlikely to be competitive.
[2]
Question 35
The pathway that produces isoleucine from threonine includes several enzyme-catalysed steps. Threonine deaminase catalyses the first committed step. The activity of threonine deaminase was measured at different isoleucine concentrations.
Describe the effect of increasing isoleucine concentration on threonine deaminase activity.
[1]
Explain how the data provide evidence for feedback inhibition.
[2]
Suggest why feedback inhibition is useful to the cell.
[2]
Question 36
Sucrase catalyses the hydrolysis of sucrose to glucose and fructose. The figure shows an energy model for the same reaction with and without sucrase.
I.
Explain how induced fit allows sucrase to catalyse the hydrolysis reaction.
[2]
II.
Explain what the figure shows about the effect of sucrase on activation energy.
[2]
Compare the role of sucrase with the role of sucrose in this reaction.
[1]
Evaluate the usefulness of an energy profile graph as a model of enzyme action.
[2]
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Question 37
The diagram represents part of metabolism in a liver cell, including glycogen formation, glycogen breakdown, amino acid polymerization and oxidation of glucose during respiration.
I.
Compare anabolic and catabolic reactions using examples from the diagram.
[2]
II.
Distinguish condensation and hydrolysis reactions in metabolism.
[2]
Explain why enzyme specificity is important in a network of interdependent metabolic reactions.
[3]
Question 38
A protease extracted from seeds has a narrow pH range for activity. Outside this range, the rate of protein digestion decreases rapidly.
I.
Explain how the three-dimensional structure of an enzyme produces a functional active site.
[2]
II.
Explain why changes in pH reduce protease activity away from the optimum.
[2]
Discuss why denaturation can reduce enzyme-substrate specificity even if the condition causing denaturation does not act directly on the active site.
[3]
Question 39
The activity of a membrane-embedded enzyme was measured at increasing concentrations of a soluble substrate. The enzyme molecules were fixed in the membrane, but the substrate molecules were free to diffuse.
I.
Describe the relationship between substrate concentration and reaction rate shown in the graph.
[2]
II.
Explain the relationship using molecular motion and substrate-active site collisions.
[2]
Evaluate the use of the smooth curve as a biological model for these experimental results.
[3]
Question 40
In mammals, digestive enzymes are secreted into the gut lumen, while enzymes of glycolysis and the Krebs cycle act inside cells. Metabolic reactions also contribute to body temperature regulation.
I.
Compare intracellular and extracellular enzyme-catalysed reactions.
[2]
II.
Explain why extracellular digestion is useful before absorption.
[2]
Discuss the role of metabolic heat generation in mammals.
[3]
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Question 41
Penicillin inhibits bacterial transpeptidase, an enzyme involved in cross-linking peptidoglycan in bacterial cell walls. Two bacterial strains were tested. Strain A is susceptible to penicillin. Strain B has an altered transpeptidase.
Compare the effect of penicillin on transpeptidase activity in strain A and strain B.
[2]
Explain why the persistence of inhibition after washing supports mechanism-based inhibition.
[2]
Suggest how the altered transpeptidase in strain B could confer resistance to penicillin.
[1]
Question 42
Catalase activity was investigated using potato extract and hydrogen peroxide. Oxygen production was used as a measure of enzyme activity at different temperatures.
I.
Deduce the optimum temperature for catalase in this investigation.
[1]
II.
Explain the shape of the temperature curve.
[3]
Explain how increasing hydrogen peroxide concentration would affect catalase activity if temperature was kept at the optimum.
[2]
Evaluate two aspects of the experimental design that should be controlled to make the temperature results valid.
[2]
Question 43
A student measured oxygen released by catalase from hydrogen peroxide using a gas syringe. The graph shows cumulative oxygen volume against time.
I.
Determine the initial rate of reaction from the tangent shown on the graph. Show your working.
[2]
II.
Explain why the initial rate is usually more useful than the rate calculated from the whole graph.
[2]
Suggest two improvements or precautions for this catalase investigation.
[2]
Question 44
The figure compares simplified representations of glycolysis, the Krebs cycle and the Calvin cycle.
I.
Distinguish linear and cyclical metabolic pathways using examples from the figure.
[2]
II.
Explain why regeneration of an intermediate is essential in a cyclical pathway.
[2]
Evaluate the likely effect of inhibiting one enzyme in the middle of a metabolic pathway.
[3]
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Question 45
The pathway for isoleucine synthesis begins with threonine. Isoleucine can bind to threonine deaminase, the enzyme catalysing the first committed step.
I.
Explain how isoleucine regulates its own synthesis by feedback inhibition.
[3]
II.
Explain why this is an example of negative feedback.
[2]
Evaluate the advantage of inhibiting the first committed step rather than a later step in the pathway.
[2]
Question 46
A regulatory molecule R binds reversibly to an enzyme at a site separate from the active site. The effect of R was tested at different substrate concentrations.
I.
Explain how binding of R at an allosteric site can reduce enzyme activity.
[3]
II.
Compare reversible non-competitive inhibition with irreversible mechanism-based inhibition.
[2]
Evaluate whether the graph supports the conclusion that R is a non-competitive inhibitor.
[2]
Question 47
An enzyme was tested at increasing substrate concentrations with no inhibitor, with inhibitor X and with inhibitor Y. One inhibitor is competitive and the other is non-competitive.
I.
Identify which inhibitor is competitive and which is non-competitive, using evidence from the graph.
[2]
II.
Explain the different effects of increasing substrate concentration on competitive and non-competitive inhibition.
[3]
Statins competitively inhibit HMG-CoA reductase in cholesterol synthesis. Discuss why statin dose must be controlled.
[3]
Question 48
Penicillin inhibits bacterial transpeptidase, an enzyme required for cross-linking peptidoglycan in bacterial cell walls. Some resistant bacteria have altered transpeptidase enzymes.
I.
Explain why penicillin is described as a mechanism-based irreversible inhibitor.
[3]
II.
Explain how altered transpeptidase can confer resistance to penicillin.
[2]
Discuss why inhibition of transpeptidase can kill growing bacterial cells.
[3]
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