Syllabus Edition

First teaching 2023

First exams 2025

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Mode of Action of Enzymes (CIE AS Biology)

Exam Questions

2 hours42 questions
11 mark

Which statements are true about the optimum temperature of all enzymes?

1

It is equal to the human body temperature (36.5 – 37.5°C)

2

Enzyme/substrate complexes are formed at the quickest rate. 

3

It is the maximum temperature an enzyme will function.

4

Increasing temperature past the optimum will break bonds in the tertiary structure.

  • 1, 2 and 3 only

  • 3 and 4 only

  • 2, 3 and 4 only

  • 2 and 4 only

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21 mark

The following statements are about enzymes:

1

The speed they function at can be reduced by competitive inhibitors.

2

Their primary structure is translated from mRNA.

3

They can be embedded in the plasma membrane of a cell. 

4

They have tertiary and quaternary structures. 

Which statements are correct for all enzymes?

  • 1 and 3 only

  • 1, 2 and 3 only

  • 2, 3 and 4 only

  • All correct

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31 mark

Enzymes function optimally in detergents at temperatures between 20 and 60°C and within a pH range of 7–10.5.  The most widely used detergent enzymes efficiently break down protein, carbohydrate and fat stains.

If a washing cycle is set to run at 40°C and pH 8, which row best describes what is happening.

  protease carbodydrase lipase
A condensation of peptide bonds condensation of glycosidic bonds condensation of ester bonds
B condensation of peptide bonds hydrolysis of peptide bonds hydrolysis of ester bonds
C hydrolysis of peptide bonds hydrolysis of glycosidic bonds hydrolysis of ester bonds
D condensation of glycosidic bonds hydrolysis of ester bonds hydrolysis of peptide bonds

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    41 mark

    Which of the statements below correctly describe the roles of enzymes?

    1

    They catalyse the building of larger molecules from smaller molecules.

    2

    They cause more frequent collisions between molecules.

    3

    They lower the activation energy required to start a reaction.

    4

    They are translated from mRNA by a ribosome. 

    • All 4 statements

    • 1, 2 and 3 only

    • 2, 3 and 4 only

    • 1, 3 and 4 only

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    51 mark

    Which level(s) of protein structure arise from being made of several polypeptide chains?

    1

    Primary

    2

    Secondary

    3

    Tertiary

    4

    Quaternary

    • 2 and 3 only

    • 3 and 4 only

    • 4 only

    • All 4 statements

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    61 mark

    Which of the following statements is true of all enzymes?

    • They are soluble in water.

    • They have a quaternary structure.

    • They have only one active site.

    • They catalyse anabolic reactions.

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    71 mark

    Washing powder contains various enzymes to remove stains efficiently from clothing 

    Which of the following would be the most important for removing a butter stain from a shirt? 

    • proteases

    • lipases

    • carbohydrases

    • cellulase

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    81 mark

    During the production of fruit juice, the enzyme pectinase is used to break down pectin, a polysaccharide commonly found in the cell walls of plant cells. This releases more juice.

    What product would be formed by the hydrolysis of the cell walls?

    • α-glucose

    • cellulose

    • starch

    • β-glucose

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    91 mark

    Catalase was added to a large amount of hydrogen peroxide solution.  The volume of oxygen produced in the first five seconds was measured to be 250 cm3

    What is the initial rate of reaction in dm3 min-1?

    • 50 dm3min-1

    • 3 dm3min-1

    • 0.05 dm3min-1

    • 3000 dm3min-1

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    101 mark

    What best describes the effect of an enzyme in an enzyme-catalysed reaction?

    • Increases activation energy and has no effect on the energy yield.

    • Increase activation energy and decreases the energy yield.

    • Decreases activation energy and has no effect on the energy yield.

    • Decreases activation energy and increase the energy yield.

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    11 mark

    Biological washing detergents use enzymes to efficiently break down food stains.  They contain protease, carbohydrase and lipase.  As the optimum temperatures for these enzymes is around 40°C, they allow washing to be conducted at lower temperatures and so are seen to be environmentally friendly.  

    Which of these would be the washing advice on a packet of biological detergent? 

      wash silk clothing 90°C wash cycle remove blood stains

    A

    B

    C

    D

    yes

    yes

    no

    no

    yes

    no

    no

    no

    Yes

    Yes

    No

    Yes

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      21 mark

      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.

      What is the correct reason for this?

      • hydrolysed products will decrease the pH

      • lipase has a very low optimum pH

      • hydrolysed products will increase the pH

      • the addition of water molecules produced by hydrolysis decreases pH

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      31 mark

      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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      41 mark

      The graph below shows the activation energy of an enzyme-catalysed reaction, and the same reaction without a catalyst.

      What is the value of activation energy for the enzyme-catalysed reaction?

      q4

      • 0

      • 5

      • 20

      • 25

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      51 mark

      Which levels of protein structure always determine the specificity of an enzyme?

      1 Primary
      2 Secondary
      3 Tertiary
      4 Quaternary, when present
      • 1, 2 and 3 only

      • 3 and 4 only

      • 2, 3 and 4 only

      • All 4 statements

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      61 mark

      Which of the following statements about enzymes is not correct?

      • They can have multiple active sites.

      • They are comprised 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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      71 mark

      Which type of bonds would be the last to break when an enzyme is heated above its optimum temperature?

      • Hydrogen

      • Hydrophobic interactions

      • Ionic

      • Disulfide bridges

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      81 mark

      Why do large increases in temperature or pH reduce the rate of reaction in enzymes?

      1 They disrupt ionic bonds.
      2 They change the three-dimensional shape of the enzyme
      3 They increase hydrophobic interactions.
      4 They cause changes in the hydrogen bonds.
      • All 4 statements

      • 1, 2 and 3 only

      • 2, 3 and 4 only

      • 1, 2 and 4 only

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      91 mark

      Colorimeters are often used in biology to provide quantitative data on the rate of enzyme activity. 

      Which of the following statements about colorimeters is not true?   

      • A beam of light with a specific wavelength is passed through a solution.

      • Any light passing though the solution is produced by a light measuring device.

      • The colorimeter calculates the absorbance or percentage transmittance.

      • Colorimeters can be used to compare different samples.

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      101 mark

      The graph below shows the activation energy of an enzyme-catalysed reaction and the same reaction without a catalyst.

      tbMVSp9m_q4

      Which values represent the activation energy of the uncatalysed reaction?

      • 15 to 30

      • 20 to 25

      • 20 to 30

      • 25 to 30

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      11 mark

      The breakdown of hydrogen peroxide to water and oxygen is catalysed by the enzyme catalase.  In an investigation into the effect of pH on the rate of reaction of catalase, potato cubes were added to hydrogen peroxide.

      Which of these would not be a control variable in this experiment?

      • the temperature

      • the mass of potato cubes added at the start

      • the amount of oxygen

      • the volume of hydrogen peroxide added at the start

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      21 mark

      Phenylalanine is one of the nine amino acids necessary to sustain human life. Other molecules can bind directly to the surface of phenylalanine and undergo chemical reactions. The chemical reaction facilitated involves the breakdown of a large molecule into two parts, a process termed hydrolysis.

      Which level of protein structure is most important for this hydrolysis reaction?

      • None

      • Secondary

      • Tertiary

      • Quaternary

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      31 mark

      The graph shows the activation energy of an enzyme-catalysed reaction and the same reaction without a catalyst.

      tbMVSp9m_q4

      Which of the following statements is not true?

      • The reaction is exothermic.

      • The activation energy of the catalysed reaction is double the uncatalyzed reaction.

      • The enzyme has almost halved the activation energy.

      • The products have less energy than the reactants.

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      41 mark

      The diagram below shows a metabolic pathway that generates an important hormone: 

      reactant space rightwards arrow with enzyme space 1 on top space intermediate space straight X space rightwards arrow with enzyme space 2 on top space space intermediate space straight Y space rightwards arrow with enzyme space 3 on top space hormone space

      A metabolic poison is able to slow the production of the hormone by inhibiting one or more of the enzymes in the pathway.  The effect of adding this poison is a large increase in the amount of reactant, a decrease in the amount of intermediate X, a slight increase in amount of intermediate Y and a large decrease in the amount of the hormone 

      Which enzymes is the metabolic poison targeting?

      • enzyme 1 only

      • enzymes 1 and 2 only

      • enzymes 2 and 3 only  

      • enzymes 1 and 3 only

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      51 mark

      The HIV virus produces a long polypeptide that is hydrolysed by a protease enzyme to producing several smaller peptides. The smaller peptides help the virus to successfully invade their host, so this viral protease is the target of many anti-AIDS drugs.

      Which feature is important if this drug is to be successful in preventing AIDS?

      • The ability to inhibit many types of bacterial enzyme.

      • The ability to competitively inhibit protease enzymes

      • The ability to disrupt only specific viral protease enzymes

      • The ability to non-competitively inhibit protease enzymes.

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      61 mark

      This figure shows a calibration curve for of blood samples at 5% concentration with known amounts of glucose.  An average person has a blood glucose level of around 350 mg/l when measured 30 minutes after consuming a starchy meal.  q5

      The blood of a person with type 2 diabetes was sampled 30 minutes after eating a starchy meal.  A colorimeter was used to assess the amount of glucose present in the person’s blood. To do this, first the blood sample was diluted to 1/20th of its original concentration with water (so that light could penetrate more easily). Then Benedict’s reagent was added, and the solution was heated in a water bath for five minutes.  The final step was to measure the absorbance of red light by the sample using a colorimeter.

      What absorbance value could reflect the diabetic blood sample?

      • 10%

      • 20%

      • 30%

      • 60%

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      71 mark

      The following equation shows a reversible reaction:

      screenshot-2023-05-06-225439

      In this reaction, which row best describes what is occurring?

        active site present on reaction at 1 reaction at 1 reaction at 2

      A

      B

      C

      D

      lipase

      glycerol

      glycerol

      lipase

      hydrolysis

      condensation

      condensation

      hydrolysis

      increases pH

      decrease pH

      increase pH

      decreases pH

      Condensation

      Hydrolysis

      Hydrolysis

      Condensation

                         

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        81 mark

        4-Oxalocrotonate tautomerase forms part of a bacterial metabolic pathway that catabolises several small molecules together into a larger molecule.  With a monomer size of just 62 amino acid residues, this enzyme is one of the smallest enzymes known.  However, in solution, the enzyme forms a hexamer of six identical subunits, so the active site is formed by amino acid residues from several subunits.  

        Which level of protein structure is most important in the catabolic reaction in the bacterial metabolic pathway?

        • Primary

        • Secondary

        • Tertiary

        • Quaternary

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        91 mark

        In an experiment, students were trying to determine the amount of starch in different types of flour.  They blended equal amounts of the different foods in 100 cm3 of water and then added iodine to each of the solutions.  They then took a sample from each of the blended food mixtures and analysed them with a colourimeter.  The colourimeter was set to measure the percentage transmission of dark blue light.  

        The graph below shows their results:screenshot-2023-05-06-224849

        Which food substance contained the most starch?

        • Rye flour

        • Maize flour

        • Wheat flour 

        • Oat flour

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        101 mark

        The graph below shows a calibration curve for the absorbance of different concentrations of glucose in solution. 

        q5

        Calibration curves can be used to determine the concentration of unknown samples.  A student was wanted to determine how much sucrose they had in an unknown sample using the figure above. To make their results comparable, they first added sucrase to hydrolyse the sucrose into glucose and fructose.  They then set their colourimeter to the same settings as the one used in the calibration curve and tested the unknown sample. The sample had an absorbance of 25%.  

        How much sucrose was present in the unknown solution?

        • 0 mg/l

        • 200 mg/l

        • 400 mg/l

        • 800 mg/l

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