Which of the options below refers to the features of catabolism?
E xergonic, condensation reaction, an example is polypeptide synthesis
Endergonic, hydrolysis reaction, an example is respiration
Endergonic, condensation reaction, an example is photosynthesis
Exergonic, hydrolysis reaction, an example is deamination
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1 markWhich of the following statements apply to enzymes?
They speed up the rate of chemical reactions in the body
They are fibrous proteins
The active site is where the substrate binds
The shape of the active site is complementary to the shape of the substrate molecule
I, III and IV
I, II and III
I and IV
II and III
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1 markThe following diagram shows the three stages involved in enzyme catalysis.
Which of the following provides the most accurate description of the events occurring at each stage?
| 1 | 2 | 3 |
A | The substrate collides with the enzyme | New bonds are forming within the substrate molecule | Chemical substances are released from the enzyme |
B | The substrate collides with the active site of the enzyme | The substrate is bound to the active site of the enzyme | The products are released from the active site |
C | The substrate binds to the enzyme | New chemical substances are formed while attached to the enzyme | These substances are released from the enzyme |
D | The substate collides with the active site of the enzyme | The substrate changes into different chemical substances | The products are released from the active site |
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1 markAn enzyme catalysed reaction is heated to a temperature of 65 °C.
Which of the following best explains the effect this temperature increase would have on the enzymes?
The enzyme and substrate molecules will gain kinetic energy and collide more frequently
The bonds in the enzyme will vibrate more and break, which will cause a permanent change in the shape of the active site
The bonds in the enzyme will vibrate more and break, causing a temporary change in the shape of the active site
The active site of the enzyme will permanently change shape due to the increased speed of collisions between the substrate molecule and the active site
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1 markLactase is an enzyme that is often immobilised and used in the food industry to produce lactose-free milk.
Which of the following would not be an advantage of using lactase?
Increases the sweetness of many dairy products, such as yoghurt and milk shakes
It may increase the rate of crystallisation of frozen dairy products, such as ice cream
It may increase the fermentation rate of products such as yoghurt and cheese
Lactase is able to function closer to its optimum conditions in a controlled factory environment
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1 markStudents investigated the effect of pH on catalase activity. Each experiment was repeated at a different pH value (pH = 2, 4, 7, 9, 11) and was set up as follows:
Five potato cubes of similar dimensions were used as a source of catalase
This was added to 50 cm3 of hydrogen peroxide
The volume of oxygen released from this reaction was collected in a measuring cylinder
This was used to calculate the initial rate of the reaction in dm3min-1
Which of the rows in the following table correctly identifies the variables in this experiment?
| Independent variable | Dependent variable | Control variable |
A | pH | Initial reaction rate | Volume of oxygen released |
B | Initial reaction rate | pH | Volume of hydrogen peroxide |
C | pH | Initial reaction rate | Volume of hydrogen peroxide |
D | Volume of oxygen released | pH | Initial reaction rate |
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1 markWhich of the following statements is not true about enzymes in metabolic pathways?
All metabolic reactions are catalysed by an enzyme.
All proteins are enzymes.
All enzymes are proteins.
All enzymes reduce activation energy of metabolic reactions in living organisms.
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1 markThe following statements are about enzymes:
The speed that they function at can be reduced by competitive inhibitors.
Their primary structure is translated from mRNA.
They can be embedded in the plasma membrane of a cell.
They all have quaternary structures.
Which of these statements are correct for all enzymes?
1 and 3 only
1, 2 and 3 only
2, 3 and 4 only
All of them are correct
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1 markWhich of the following sketch graphs best shows the effect of an enzyme on a biochemical reaction profile?
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1 markWhich one of the following phenomena is not a consequence of end-product inhibition in biochemical pathways?
Regulation of the pathway.
Prevention of a build-up of biochemical intermediate compounds.
Shutdown of the pathway once product levels reach zero.
Allosteric changes to an enzyme involved in the pathway.
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1 markEnzymes alter the activation energy required for a biochemical reaction to take place. Which of the following gives the best definition of activation energy?
The energy input required to break bonds in order for a reaction to take place.
The energy is released as bonds breaks in a reaction.
The energy required to allow substrates and enzymes to be closely aligned at the active site.
The energy given off when an enzyme-substrate complex forms.
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The four statements below are examples of the two types of metabolism, anabolism and catabolism.
Which one of the statements represents a type of metabolism which is different to the other three options?
Deamination of polypeptides to form urea.
Formation of glycosidic bonds between glucose and fructose.
Depletion of fat stores during a period of starvation.
Anaerobic respiration.
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The graph shows the effect of enzyme concentration on the rate of an enzyme-controlled reaction. The substrate concentration is constant.
Which statement about the graph is correct?
Between X and Z, the number of enzyme molecules is limiting.
Between Y and Z, the number of enzyme molecules is limiting.
Between X and Z, the number of substrate molecules is limiting.
Between Y and Z, the number of substrate molecules is limiting.
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The following statements apply to enzyme-catalysed reactions. Which row of the table best describes the sequence of events in an anabolic reaction?
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The graph shows the course of an enzyme-catalysed reaction at 25 °C.
Which statement about the graph is incorrect?
At X the number of available substrate molecules is high.
At X the number of enzyme/substrate complexes is the same as Y.
At Z the number of available substrate molecules is low.
At Y the number of enzyme/substrate complexes is the same as Z.
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Which statement below best describes the concept of enzyme-substrate specificity?
Enzymes and substrates fit together because they are the same type of biological molecule.
The enzyme's precise 3-D shape and chemical properties are compatible with the substrate allowing formation of enzyme-substrate complexes.
An enzyme can adapt its active site to fit a range of substrates to give maximum catalytic ability.
Projections on the enzyme's surface match projections on the substrate's surface.
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When investigating the rate of reaction of the enzyme lipase on the hydrolysis of triglycerides, the pH must be maintained to prevent the lipase denaturing.
Why might fluctuations in pH occur?
The products of hydrolysis will decrease the pH.
Lipase has a very low optimum pH.
The products of hydrolysis will increase the pH.
The water molecules produced as a byproduct of hydrolysis decreases pH.
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The breakdown of hydrogen peroxide to water and oxygen is catalysed by the enzyme catalase. In an investigation into the effect of temperature on the rate of reaction of catalase, mashed liver (which contains catalase) was added to hydrogen peroxide.
What would the independent variable be in this experiment?
The change in mass of the liver after a given time.
The temperature of the solution.
The mass of liver added at the start.
The volume of oxygen produced.
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Which of the following statements about enzymes is not correct?
They can have multiple active sites.
They are composed of one (or more) polypeptide chain(s).
Ester bonds play an important role in maintaining shape.
They catalyse both anabolic and catabolic reactions.
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A bacterial enzyme from the species Caldicoprobacter algeriensis can be immobilised onto polymethacrylate beads for the conversion of glucose into fructose in the food industry, as shown in the diagram below.
What is the name of the enzyme that is immobilised on the polymethacrylate beads?
Glucose isomerase.
Fructose convertase.
Fructose isomerase.
Glucose convertase.
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Enzymes can be immobilised in various ways. The diagram below shows two different ways of immobilisation.
Immobilised lactase enzymes are used to make milk digestible for lactose intolerant people. A student carried out an investigation to compare the activity of the enzyme lactase that had been immobilised in the two different ways shown.
A solution containing 50 mg cm–3 of lactose was poured through a column containing the immobilised enzyme.
What would be the best choice of dependent variable for this experiment?
The concentration of lactose in the solution before pouring through the column.
The concentration of glucose in the milk after pouring through the column.
The concentration of enzyme remaining in the column.
The temperature of the solution as it exits the column.
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A student wished to use a starch solution of 0.01% for an enzyme experiment. A stock solution of 1.0% starch solution was provided.
Which of the following dilutions would be the best method to achieve the desired concentration with greatest precision, using standard laboratory equipment?
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Which of the following statements about metabolism are correct?
Metabolism involves chemicals called metabolites.
Metabolism involves reactions in a linear chain.
Metabolism involves reactions in a cycle.
Metabolism involves only the breakdown of molecules.
I and IV only
II and III
All of the statements
I, II and III
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The graph below shows the energy changes during a reaction.
What effect would adding an enzyme have on the energy changes of the reaction?
Reduction in energy at A
Reduction in energy at B
Reduction in energy at C
Reduction in energy at D
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What is the difference between a competitive and non-competitive inhibitor?
| Competitive inhibitor | Non-competitive inhibitor |
A | Interferes with active site | Interferes with an alternative site |
B | Interferes with an alternative site | Interferes with the active site |
C | Changes the active site | Changes the substrate |
D | Changes the substrate | Changes the active site |
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Cyanide ions are an example of an allosteric inhibitor that targets the enzyme cytochrome c oxidase in aerobic respiration.
Which row best describes the action of cyanide ions?
| Can bind to an alternative site | Can bind to the active site |
A | Yes | Yes |
B | Yes | No |
C | No | Yes |
D | No | No |
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Isoleucine can be described as an end-product inhibitor.
Which statement best describes the action of isoleucine?
It acts as a competitive inhibitor to threonine and it binds to an allosteric site on threonine deaminase.
It acts as a competitive inhibitor to threonine and it binds to the active site on threonine deaminase.
It acts as a non-competitive inhibitor to threonine and it binds to an active site on threonine deaminase.
It acts as a non-competitive inhibitor to threonine and it binds to an allosteric site on threonine deaminase.
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Which graph shows the rate of a reaction taking place in the presence of a competitive inhibitor compared to the rate of a reaction in the absence of an inhibitor?
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The table below gives information on the rates of several enzyme-catalysed reactions.
Rate of reaction / product formed sec⁻¹ | Enzyme |
1.0 x 10⁶ | Citrate synthase |
5.2 x 10³ | Aconitase |
9.2 x 10⁴ | Fumarase |
3.7 x 10⁷ | Malate dehydrogenase |
Which enzyme catalyses the reaction with the fastest rate of product formation?
Citrate synthase
Aconitase
Fumarase
Malate dehydrogenase
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Which statement best describes how to calculate the initial rate of a reaction from a graph such as the one below?
Draw a tangent that crosses the origin and that corresponds to the first part of the curve, calculate the rate by dividing change in volume by change in time.
Draw a tangent that corresponds to an area part way along the curve, calculate the rate by dividing change in volume by change in time.
Draw a tangent that crosses the origin and that corresponds to the first part of the curve, calculate the rate by dividing change in time by change in volume.
Draw a tangent that corresponds to an area part way along the curve, calculate the rate by dividing change in time by change in volume
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1 markThe activity of two types of protease enzymes was measured in two different species of fish; species X and species Y. Protease enzymes are responsible for breaking down proteins into amino acids. The results of the research are shown in the graph.
The unit U denotes the enzyme required for the production of 1 μmol of product per minute. The bars represent the standard deviation.
Which statement about protease enzymes is correct?
The activity of the stomach protease of species Y is 2.5 times greater than that of species X.
The activity of the intestinal protease of species X is significantly higher than the stomach protease of species X.
The activity of the stomach protease of species X is 3.5 times less than that of species Y.
The activity of the intestinal proteases of both species X and Y are significantly higher than the stomach proteases.
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1 markThe following graph shows the change in energy that occurs during an enzyme catalysed reaction.
Which of the following would be the most accurate description of this graph?
This is an anabolic reaction that releases energy. Large, complex molecules are broken down into smaller, simpler ones during hydrolysis reactions.
This is a catabolic reaction that releases energy. Large, complex molecules are broken down into smaller, simpler ones during hydrolysis reactions.
This is an anabolic reaction that requires an input of energy. Large, complex molecules are formed from smaller, simpler ones during condensation reactions.
This is an catabolic reaction that requires an input of energy. Large, complex molecules are formed from smaller, simpler ones during condensation reactions.
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1 markBeetroot (Beta vulgaris) is a root vegetable with a characteristic red colour that is due to the pigment betanin found within the vacuoles of beetroot cells.
Scientists investigated the effect of temperature on the release of betanin from the beetroot cells. This was recorded as the mean absorbance when using a colorimeter, with a higher absorbance indicating more pigment released. The scientists deduced that the pigment is released when the membrane proteins of the tonoplast surrounding the vacuole denature.
The graph below shows their results.
Which of the following descriptions would best explain the point where enzymes start to denature inside the beetroot cells?
Enzymes would denature at 30°C. At this point, the amount of pigment released from the beetroot cells is increasing and this indicates denaturing of the membrane proteins of the vacuole
Enzymes would denature when the temperature inside the beetroot cells increase to above 40°C. This is the point when membrane proteins begin to denature and release more pigment
The enzymes inside the beetroot cells would start to denature at 50°C. The greatest amount of pigment is released from the cells at this point which indicates that the membrane proteins of the vacuole are fully denatured
At temperatures above 60°C, the enzymes inside the beetroot cells will be denatured. Most of the pigment has been released at this point, indicating that the membrane proteins of the vacuole are denatured
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1 markScientists extracted enzymes from different parts of the digestive tract of a mammal. The containers of enzyme samples got mixed up with each other before the scientists could label them. In order to identify the enzymes, they monitored the enzyme activity of each sample at different pH levels to determine the optimum pH for each.
The graph below shows the results for two of the samples (X and Y).
Which of the following would be the most valid conclusion that the scientists can draw from these results?
Enzyme X is from the stomach of the mammal since it performs at an optimum when conditions are acidic, while enzyme Y is most likely from the mouth of the mammal where conditions are more neutral
Enzyme X is from the stomach of the mammal since it performs at an optimum when conditions are acidic, while enzyme Y is most likely from the small intestine of the mammal where conditions are more alkaline
Enzyme Y is from the stomach of the mammal since it performs at an optimum when conditions are acidic, while enzyme X is most likely from the small intestine of the mammal where conditions are more alkaline
Enzyme Y is from the mouth of the mammal since it performs at an optimum when conditions are neutral, while enzyme X is most likely from the small intestine of the mammal where conditions are more alkaline
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1 markβ-glucosidases are a diverse group of enzymes which hydrolyse glycosidic bonds and are present in a wide variety of organisms. One of their uses in the food industry is the hydrolysis of bitter compounds during juice extraction to increase the sweetness of the final product. These enzymes are often immobilised when used in the food industry to increase production and save on costs.
Scientists compared the activity of free β-glucosidase to that of immobilised β-glucosidase over a range of different temperatures. Their results are shown in the graph below.
Which of the following would be the most valid comparison between free and immobilised β-glucosidase?
Immobilised β-glucosidase activity increases at a faster rate, compared to the free enzyme, for temperatures below the optimum, however, activity decreases at a slower rate for temperatures above the optimum temperature
The activity of free β-glucosidase decreases at a lower rate for temperatures above the optimum, compared to the immobilised enzyme. At 60°C there is a 400% increase in rate of activity
The activity of immobilised β-glucosidase decreases at a lower rate for temperatures above the optimum, compared to the free enzyme. At 60°C there is a 400% higher rate of activity
The activity of free β-glucosidase increases at a faster rate for temperatures below optimum compared to the immobilised enzyme, however, activity decreases at a slower rate above the optimum temperature
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1 markStudents investigated the effect of starch concentration on the activity of amylase.
They used a 1% starch solution and made two dilutions of 0.1% and 0.01%
They added 10 cm3 of amylase to each of the three test tubes
They took samples of each solution at 10 second intervals for 30 seconds in total
Iodine solution was added to each sample to test for the presence of starch
They came to the conclusion that the amylase did not properly break down the starch
Their teacher suggested that the students could achieve some more useful results by making some simple improvements to their experimental design.
Which of the following would represent the best improvements to their experimental design?
More dilutions should have been done over a smaller range of concentrations, there should have been multiple test tubes for each concentration and the experiment should have been conducted for at least 2 minutes
More dilutions should have been done over a greater range of concentrations, there should have been multiple test tubes for each concentration and the experiment should have been conducted for at least 30 minutes
More dilutions should have been done over a greater range of concentrations, there should have been multiple test tubes for each concentration and the experiment should have been conducted for at least 2 minutes
More dilutions should have been done over a smaller range of concentrations, there should have been multiple test tubes for each concentration and the experiment should have been conducted for at least 30 minutes
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1 markThis diagram shows a metabolic pathway occurring in an organelle. The speed of this metabolic pathway is self-regulating as the end product acts as a competitive inhibitor to enzyme 2.
| enzyme 1 |
| enzyme 2 |
| enzyme 3 |
|
reactant | → | intermediate X | → | intermediate Y | → | end product |
What would you expect not to occur when adding an additional end product to the organelle?
Enzyme 2's activity will decrease
The amount of intermediate Y would decrease
The amount of reactant would increase
The amount of intermediate X would increase
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1 markIn the graph, Z represents the relationship between the initial rate of an enzyme-catalysed reaction and the concentration of its substrate under optimal conditions and without an inhibitor.
Which curve would represent the same experiment carried out in the presence of a low concentration of a non-competitive inhibitor?
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1 markThe graphs in A - D show the progress of an enzyme-catalysed reaction, measured by the volume of product released from the reaction mixture over time.
Which graph best depicts how a scientist would establish the average rate of reaction over the first minute of the reaction?
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1 markThe enzyme catalase was added to a large volume of hydrogen peroxide solution. The volume of oxygen produced in the first five seconds was measured at 250 cm3.
What is the initial rate of reaction in dm3 min-1 ?
50 dm3 min-1
3 dm3 min-1
0.05 dm3 min-1
3 000 dm3 min-1
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