A LevelBiologyCIEExam Questions2. Biological Molecules2.3 Proteins

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First teaching 2023

First exams 2025

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Proteins (CIE A Level Biology)

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2.3 Proteins

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2.3 Proteins

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11 mark

The diagram shows a biological molecule found in cells.

Which arrow labels a peptide bond?

screenshot-2023-05-03-151424

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    21 mark

    The tertiary structure of a protein molecule is maintained by which bonds?

      peptide hydrogen disulfide ionic
    A X ✓ X ✓
    B ✓ ✓ X X
    C X ✓ ✓ ✓
    D ✓ X ✓ X

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      31 mark

      The protein myoglobin has a similar function to haemoglobin except myoglobin does not have a quaternary structure.

      Why does myoglobin not have a quaternary structure?

      • Myoglobin has only one polypeptide chain.

      • Myoglobin has a fibrous rather than a globular structure.

      • Myoglobin does not contain a haem group.

      • Myoglobin does not contain any alpha helices.

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      41 mark

      Which of the following statements about fibrous proteins is incorrect?

      • They are very sensitive to changes in heat.

      • They are insoluble.

      • They are used as structural proteins.

      • The often form long coils.

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      51 mark

      How can the quaternary structure of haemoglobin be described?

      1. a specific order of amino acids
      2. a globular structure
      3. an α-helix
      4. a dipeptide
      5. four polypeptide chains connected together 

      • 5 only

      • 2, 3 and 5

      • 1, 2 and 3

      • 2 and 5

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      61 mark

      Which description of collagen is correct?

      • Three collagen fibres coil around each other to form a strong, insoluble structure termed a triple helix.

      • Both amino acids of the same polypeptide and amino acids of different polypeptides are joined by peptide bonds.

      • The smallest amino acid, glycine, is found in a high proportion in collagen.

      • Collagen polypeptides consist of many alpha helices in a regular spiral arrangement.

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      71 mark

      Protein X is a transport protein found dissolved in blood plasma and is used to transport different things around the body. It contains six internal disulfide bridges and has a roughly spherical shape.

      Protein Y is a structural protein found in the hair and nails of mammals. It is made of two alpha-helices twisted round each other to make a coiled coil.

      Are albumin and keratin examples of globular or fibrous proteins? 

      • Both are globular proteins

      • Both are fibrous proteins

      • X is globular, Y is fibrous

      • Y is globular, X is fibrous

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      81 mark

      In protein molecules, which bonds are responsible for producing the primary, secondary and tertiary structure? 

        level of structure
      primary secondary tertiary
      A covalent ionic ionic
      B ionic hydrogen covalent
      C peptide hydrogen disulfide
      D covalent ionic hydrogen

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        91 mark

        Two amino acids, both containing two carboxylic acid (-COOH) groups are illustrated below. 

        q9

        Which labelled groups take part in the formation of a dipeptide of these amino acids? 

        • 1 and 5

        • 2 and 3

        • 2 and 4

        • 1 and 4

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        101 mark

        The protein haemoglobin contains iron. 

        What is the role of iron within the molecule?  

        • It undergoes reduction and oxidation (redox) reactions

        • It stabilizes the quaternary structure of haemoglobin

        • It enables haemoglobin to dissolve in red blood cells

        • It binds oxygen to haemoglobin

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        11 mark

        Protein molecules contain multiple different types of bond, some of which are stronger than others.

        Which is the correct order from weakest to strongest? 

        • disulfide bonds, ionic bonds, hydrogen bonds, hydrophobic interactions

        • ionic bonds, disulfide bonds, hydrophobic interactions, peptide bonds

        • hydrophobic interactions, hydrogen bonds, peptide bonds, ionic bonds

        • hydrophobic interactions, hydrogen bonds, disulfide bonds, peptide bonds

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        21 mark

        Amino acids consist of oxygen, hydrogen, carbon and nitrogen atoms. The diameter of each atom when bonded to another atom is shown in the table below.

        atom single bond / nm double bond / nm
        O
        H
        C
        N        		 0.13
        0.06
        0.154
        0.14        		 -
        0.110
        0.120
        0.134

        Using the figures in the table, the approximate length of one amino acid is 0.7nm.

        2-3-diagram-3

        What is the approximate length of a dipeptide of this amino acid?

        • 1.0 nm

        • 1.2 nm

        • 1.4 nm

        • 1.6 nm

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        31 mark

        Haemoglobin carries oxygen in the blood. 

        Which of the following best describes why this is possible? 

        1

        Oxygen binds to iron reversibly 

        2

        Oxygen binding causes haemoglobin to change shape

        3

        Oxygen binds to the haem group

        • 1 only

        • 1 and 2

        • 2 and 3

        • 1, 2 and 3

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        41 mark

        A protein entirely made from repeating residues of the same amino acid was produced. 

        The graph shows the structure of this protein molecule at different pH values.q-14-cie-2-3

        Which statement is true?

        • At pH2 the protein has lost its secondary structure

        • At pH2 the protein has lost its tertiary structure

        • At pH10 the protein has lost its primary structure

        • At pH10 the protein has lost its secondary structure

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        51 mark

        The structure of collagen is illustrated in the diagram below.

        Which label correctly identifies a molecule of collagen?

        screenshot-2023-05-15-143613

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          61 mark

          Which of the following causes fibrous proteins to be insoluble?

          • They are very long

          • Their surface has non polar amino acids

          • They are usually structural

          • They have more than one polypeptide chain

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          71 mark

          Which row of statements describes haemoglobin correctly? 

          A

          polypeptide chains interact to produce an almost spherical molecule

          an iron ion is present within each haem group

          quaternary structure of two alpha chains and two beta chains

          each molecule can transport a total of four oxygen atoms

          B

          four polypeptide chains, each containing a prosthetic group

          iron ions can associate with oxygen forming oxyhaemoglobin

          in each chain, hydrophobic R groups of amino acids point towards the centre of the molecule

          at 50 % saturation, two oxygen molecules are transported by the molecule

          C

          polypeptide chains produce a loose helical shape, which curls to form a spherical molecule

          iron ions in the molecule can bind reversibly with oxygen

          in each chain, hydrophobic R groups of amino acids surround the iron ion

          each molecule can transport a total of eight oxygen atoms

          D

          polypeptide chains interact to produce a globular chain

          each chain contains a prosthetic group of amino acids surrounding an iron 

          two identical alpha chains and two identical beta chains

          each chain can transport an oxygen molecule

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            81 mark

            Which of the following facts about collagen explain its role in muscles and tendons?

            1 Collagen is insoluble
            2 Collagen chains form a helical structure
            3 Different collagen molecules are bonded together by covalent bonds
            4 Collagen is made of amino acids with small R groups

            • 1 and 2

            • 1, 2 and 3

            • 2, 3 and 4

            • All

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            91 mark

            The diagram shows a polypeptide of the protein glutenin, which has an important role in maintaining the strength and elasticity of bread dough.

            screenshot-2023-05-15-145320

            What is the structure of glutenin and why? 

             

            Structure

            Reason

            A

            Secondary

            the loose spiral is an alpha helix

            B

            Tertiary

            a 3D shape is formed from the different regions

            C

            Quaternary

            there are globular and fibrous regions

            D

            Quaternary

            the structure consists of spiral and coiled regions 

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              101 mark

              Every amino acid has an R group which gives the molecule its properties. The diagram below shows the R groups for the amino acids Arg, Ser, Glu and Val.

              screenshot-2023-05-15-145530

               

              Acidic

              Basic

              Hydrophilic

              Hydrophobic

              A

              Glu

              Arg

              Ser

              Val

              B

              Ser

              Arg

              Glu

              Val

              C

              Glu

              Val

              Ser

              Arg

              D

              Arg

              Val

              Glu

              Ser

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                11 mark

                What describes a globular protein that is not soluble in water?

                • having amino acids with polar R groups facing out

                • having amino acids with hydrophobic R groups facing out

                • having amino acids with hydrophilic R groups facing out

                • having a central core of amino acids with hydrophobic R groups

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                21 mark

                Four proteins 1, 2, 3 and 4 are described below

                1

                consists of four polypeptides each with a prosthetic group

                2

                consists of a globular tertiary structure with a binding site

                3

                consists of four polypeptides held together by disulfide bonds

                4

                consists of three polypeptides tightly coiled together

                Which description matches the proteins collagen, haemoglobin and the enzyme lipase? 

                 

                Collagen

                Haemoglobin

                Lipase

                A

                1

                3

                4

                B

                3

                2

                1

                C

                4

                3

                2

                D

                4

                1

                2

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                  31 mark

                  An experiment was undertaken to test the permeability of the plasma membrane and tonoplast of beetroot cells in various different chemicals. Vacuoles of beetroot cells carry a red pigment which cannot diffuse through their plasma membranes and tonoplasts to leave the cell.

                  The beetroot was cut into equal 1 cm3 cubes before being washed under a tap for 15 minutes to remove pigment released from outer damaged cells. The cubes were then placed in the various solutions, all of which turned red.

                  The table below shows four possible behaviors of phospholipids and proteins in different solutions, which is correct?

                    solution protein denatures solution phospholipids dissolve
                  A ethanol ✓ dilute HCl ✓
                  B dilute HCL ✓ ethanol ✓
                  C ethanol ✓ 40°C water ✓
                  D 40°C water ✓ dilute HCl ✓

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                    41 mark

                    A total of four polypeptide chains, 2 alpha chains and 2 beta chains, make up a globular protein called Haemoglobin. In normal cases, the DNA code for each beta chain for glutamic acid in the sixth triplet.

                    However, Sickle cell anaemia in individuals causes the base triplet to change and code for valine instead.

                    This mutation changes one aspect of the haemoglobin molecule. Which is it?

                    • the quaternary structure

                    • the iron content

                    • the secondary structure

                    • the primary structure

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                    51 mark

                    When leaving the lungs, haemoglobin is 98 % saturated. 

                    How many oxygen atoms will be carried by the majority of haemoglobin molecules?

                    • 2

                    • 4

                    • 6

                    • 8

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                    61 mark

                    There is estimated to be 20,000 genes in the human body, but over 300,000 proteins.

                    If a chain consists of y amino acid residues and there are no different amino acids available, how many different polypeptides can be made?

                    • ny

                    • nitalic cross timesy

                    • yn

                    • n / y

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                    71 mark

                    The diagram shows a fibrous and globular protein with three amino acids labelled 1, 2 and 3. Amino acids 1 and 2 are on the outer surface of the protein whereas amino acid 3 in internal.

                    qn-26

                    Which row identifies the most likely amino acid R group at each point?

                      R group
                      1 2 3
                    A H CH(CH3)2 CH(CH3)2
                    B H (CH2)4NH2 CH2OH
                    C CH3 CH(CH3)2 (CH2)4NH2
                    D CH3 CH2OH CH(CH3)2

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                      81 mark

                      The graph shows the effect of pH on enzyme activity.

                      qn-29

                      Which of the following R groups in the active site will be directly affected by pH?

                      • -CH3

                      • -CH2OH

                      • - CH2SH

                      • - (CH2)4NH

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                      91 mark

                      A protein found in the stomach is placed in water, this causes the protein to denature. 

                      Which of the following bonds are affected?

                      qn-30

                      • 1 only

                      • 1, 3 and 4

                      • 1 and 4

                      • All

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