IBBiologyHLExam QuestionsForm & FunctionProteins

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First teaching 2023

First exams 2025

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Proteins (HL IB Biology)

Exam Questions

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Proteins

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1
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The following diagram shows a dipeptide with various parts of the molecule numbered (1 to 4).

e-1

Which row of the table below correctly identifies each labelled part of this dipeptide?

  1 2 3 4
A. Carboxyl group Peptide bond R-group Amino group
B. R-group Amino group Peptide bond Carboxyl group
C. Amino group Carboxyl group Peptide bond R-group
D. Amino group Peptide bond R-group Carboxyl group

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    2
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    Which of the following is not a function of proteins?

    • Involved in the formation of the cytoskeleton within a cell that facilitates chromosome movement

    • Act as a store of chemical potential energy in cells

    • Act as chemical messengers that are secreted by glands and act on different parts of the body

    • They may speed up chemical reactions within a cell

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    3
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    A simple tetrapeptide consists of four amino acids.

    How many different combinations of amino acids would be possible for this peptide?

    • 16 000

    • 160 000

    • 1 600 000

    • 16 000 000

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    4
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    Which of the following are ALL examples of proteins?

    • Rubisco, collagen, amylopectin

    • Amylopectin, collagen, guanine

    • Insulin, amylose, spider silk

    • Rhodopsin, immunoglobulins, rubisco

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    5
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    Which of the following would represent all the elements that are present in proteins?

    2-3easyq5

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      6
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      Which of the following is involved in the secondary structure of a protein?

      1. Double helix
      2. β-pleated sheets
      3. Hydrogen bonds
      4. Hydrophobic interactions

      • I. and II. 

      • II. and III.

      • I., II. and III. 

      • II., III. and IV.

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      11 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 0.13 -
      H 0.06 0.110
      C 0.154 0.120
      N 0.14 0.134

      Using the figures in the table, the approximate length of one amino acid is 0.7 nm, as shown below.q1-2-3-proteins-medium-ib-hl-biology

      What would be the approximate length of a dipeptide of this amino acid after a condensation reaction has occurred?

      • 1.0 nm 

      • 1.2 nm

      • 1.4 nm

      • 1.6 nm 

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      21 mark

      Which of the following chemical groups does not bond directly with the central carbon of an amino acid?

      • ‒OH

      • ‒NH2

      • ‒COOH

      • ‒H

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      31 mark

      All life (except for a few primitive, prokaryotic species) use the same 20 amino acids joined into polypeptides.

      Which of the four statements above is not a possible hypothesis for why all life uses the same 20 amino acids?

      • Only the 20 amino acids existed when life began, so all life now uses them.

      • All organisms share a common ancestor, so the link between the genetic code and amino acids sequences is already fixed. 

      • Polypeptide chains join together to increase the range of possible functions that they can carry out

      • 20 amino acids is more than enough to give a huge, almost infinite range of characteristics for all life. 

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      41 mark

      Which of the following causes fibrous polypeptides to be insoluble?

      • They are very long.

      • Their surface has nonpolar amino acids.

      • They are usually structural.

      • They have more than one polypeptide chain.

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      51 mark

      Which row of the table best classifies common proteins with differing numbers of polypeptide chains?

        One polypeptide chain Two polypeptide chains Three polypeptide chains
      A Collagen Insulin Haemoglobin 
      B Lysozyme Insulin Collagen
      C Lysozyme Haemoglobin Insulin
      D Haemoglobin Lysozyme Collagen

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        61 mark

        Which of the following words best describes the structure of a large macromolecule (such as a protein) and its final 3-D shape?

        • Presentation

        • Structure

        • Confirmation

        • Conformation

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        71 mark

        Which of the following statements about the proteome is correct?

        • The proteome is the full range of proteins that an organism could produce from its genome. 

        • The proteomes of closely related people are identical. 

        • The proteome is usually smaller than the genome of an organism. 

        • The proteome varies during an organism’s lifetime. 

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        81 mark

        Which of the following diagrams correctly shows the structure of a dipeptide?

        q8-2-3-proteins-medium-ib-hl-biology

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          91 mark

          When using molecular visualisation software to represent large biological molecules, which aspect of a macromolecule would not necessarily be distinguishable?

          • The surface topography (eg. of a cell-surface receptor).

          • The location of the active site of an enzyme.

          • The flexing of a molecule when in aqueous solution.

          • The presence of a cavity to show an ion channel through a membrane protein.

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          101 mark

          Which interactions or features differentiate tertiary structure from secondary structure in proteins?

          1. Hydrogen bonds
          2. Disulphide bridges
          3. Hydrophobic interactions
          4. Alpha-helices
          5. Interactions between R-groups of amino acids

          • I and II

          • II and V

          • II, III and IV 

          • II, III and V

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          111 mark

          Which of the following best describes the quaternary structure of proteins?

          • The three-dimensional structure of a polypeptide chain

          • Arrangement of beta-pleated sheets

          • The linear sequence of amino acids

          • How polypeptide chains are arranged

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          11 mark

          The formation of the 3D shape of a globular protein relies on hydrophobic and hydrophilic interactions. 

          Which of the statements below correctly describes this process? 

          • When peptide bonds form, the condensation reaction releases water, which forms hydrogen bonds with the hydrophilic R groups of the amino acids.

          • Certain hydrophilic amino acid R groups are able to form hydrogen bonds with other hydrophilic amino acids R groups on different proteins.

          • Hydrophobic R groups of amino acids are repelled by the water surrounding the protein, forcing them into the centre of the protein away from the water, and the hydrophilic R groups get pulled to the outside.

          • Hydrophilic R groups are repelled by the water and are forced away into the centre of the 3D structure, causing the shape to be distorted.

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          2
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          Human insulin is a peptide hormone consisting of 51 amino acids.

          Which of the following would represent the minimum number of bases that the gene coding for insulin would consist of?

          • 26

          • 51

          • 102

          • 153

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          3
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          Trypsin is a digestive enzyme found in pancreatic juices that breaks down proteins into polypeptides in the small intestine. The image below represents the three dimensional structure of trypsin.

          2-3hardq2

          Image courtesy of 0fb1d8. Licensed under Creative Commons Attribution-Share Alike 4.0 International license. Reused and distributed under conditions found at: https://creativecommons.org/licenses/by-sa/4.0/deed.en

          Which of the following would be the most accurate description of the conformation of trypsin?

          • It is a functional protein that is folded into a specific shape which is held in position by bonds between the R-groups of neighbouring amino acids, with hydrophilic R-groups facing towards the outside of the molecule

          • It is a functional protein that is folded into a specific shape which is held in position by bonds between the R-groups of neighbouring amino acids, with hydrophobic R-groups facing towards the outside of the molecule

          • It is a structural protein that is folded into a specific shape which is held in position by bonds between the R-groups of repeating amino acids

          • It is a functional protein that is folded into a specific shape which is held in position by bonds between the R-groups of neighbouring amino acids, with hydrophilic R-groups facing towards the inside of the molecule

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          4
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          Rituximab is an example of a therapeutic protein that is used to treat certain types of cancers and autoimmune diseases. It is very sensitive to temperature and pH changes and is typically injected into the bloodstream of patients.

          Which of the following statements would explain why therapeutic proteins, such as rituximab, cannot be taken orally?

          I. The molecule would vibrate so fast once in the stomach that the intermolecular bonds would break

          II. The conformation of the protein will change once in the stomach and it may become non-functional

          III. The protein may become insoluble once in the stomach and form a precipitate due to the breakage of ionic bonds

          IV. Conditions in the stomach will cause the hydrophobic R-groups of the protein to be exposed to the outside of the molecule

          • I and IV

          • I, II and III

          • II and III

          • II, III and IV

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          5
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          The denaturation of three different proteins (P, Q and R) at different temperatures were investigated. The more denatured a protein is, the less stable the molecule becomes. The following graph shows the results of this investigation.

          h-4

          Which of the following would be the most valid conclusion that the scientists can draw from these results?

          • Protein R would be less stable and had a lower rate of denaturation above 70°C compared to protein Q, while protein P was fully denatured by 80°C

          • Protein R would be more stable and had a lower rate of denaturation above 70°C compared to protein Q, while protein P was the least heat tolerant of all the proteins

          • Protein Q would be more stable and had a lower rate of denaturation below 70°C compared to protein R, while protein P was fully denatured by 80°C

          • Protein Q would be less stable and had a higher rate of denaturation below 70°C compared to protein R, while protein P was the least heat tolerant of all the proteins

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          6
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          Which of the following statements applies to both the proteome and genome of an organism?

          I. Every cell in an organism is reliant on this for its survival

          II. It is a reflection of the actual events taking place inside the cells of an organism

          III. There are slight variations present between individual organisms

          IV. It can be variable over time depending on the activities of the cell

          • I and II

          • I and III

          • I, II and IV

          • II, III and IV

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          7
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          Ustilago maydis is a fungal pathogen affecting maize. It secretes toxins, known as killer toxins, with the best-characterised one being the KP6 toxin. This particular toxin consists of two small polypeptides that are not linked by covalent bonds. The diagram below shows the ribbon structure of one of the polypeptides of the KP6 toxin.7-3_q3h

          Which of the following is the most accurate description of the structure of this polypeptide?

          • This polypeptide represents the tertiary structure of a protein due to the hydrogen bonds that form between the carboxyl group of one R-group and the amino group of another amino acid

          • This polypeptide represents the secondary structure of a protein due to the presence of hydrogen bonds that forms triple-helices and β-pleated sheets

          • This polypeptide represents the quaternary structure of a protein due to the existence of more than one chain that can fit together to form the toxin

          • This polypeptide represents the secondary structure of a protein due to the presence of hydrogen bonds that forms α-helices and β-pleated sheets

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