Lesson 3.1.4.1.2

3.1.4.1.2 Protein structure: primary to quaternary Quiz: AQA Biology, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.1.4.1.2, Protein structure: primary to quaternary: 20 multiple choice questions for the AQA Biology (7402), Unit 1: Biological molecules, written with Revision Ninja.

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The 20 questions

  1. What is the primary structure of a protein?

    • The arrangement of several polypeptide chains into one complex
    • The coiled alpha helix formed by hydrogen bonds
    • The three-dimensional shape formed by folding of the whole chain
    • The specific sequence of amino acids in the polypeptide chain

  2. Which bonds stabilise the alpha helix and beta-pleated sheet of secondary structure?

    • Disulfide bridges between cysteine side chains
    • Glycosidic bonds between adjacent amino acids
    • Ionic bonds between charged R groups
    • Hydrogen bonds between backbone C=O and N-H groups

  3. Which level of protein structure is defined by two or more polypeptide chains held together?

    • Quaternary structure
    • Primary structure
    • Tertiary structure
    • Secondary structure with no exceptions

  4. How many polypeptide chains does normal adult haemoglobin contain?

    • 1
    • 4
    • 8
    • 2

  5. Which bond is a covalent link that can stabilise the tertiary structure of a protein?

    • Glycosidic bond between two glucose units
    • Hydrogen bond between two peptide groups
    • Ionic bond between two charged side chains
    • Disulfide bridge between two cysteine residues

  6. Which types of bond help maintain the tertiary structure of a protein?

    • Glycosidic bonds and phosphodiester bonds, which hold together the sugar and nucleotide polymers only
    • Ester bonds between glycerol and fatty acids, which hold together the lipid molecules in membranes
    • Hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions
    • Hydrogen bonds between two glucose units, which hold the polysaccharide chains together in a plant

  7. What is a beta-pleated sheet?

    • A primary structure in which the sequence of amino acids forms a fixed fold through the chain backbone
    • A quaternary structure made of four identical polypeptide chains that are held together by covalent bonds
    • A secondary structure in which polypeptide chains lie side by side and are held by hydrogen bonds
    • A tertiary structure that is held together only by disulfide bridges between cysteine residues

  8. A mutation changes one amino acid in a protein's primary structure. What is the most likely effect?

    • It has no effect, because only quaternary structure determines function
    • It always stops the protein being made at all
    • It may alter how the chain folds, changing tertiary structure and possibly function
    • It changes only the number of polypeptide chains in the protein

  9. In sickle cell disease, one amino acid in a haemoglobin chain is replaced by a hydrophobic one on the surface. Which effect is most likely?

    • Haemoglobin loses all four of its polypeptide chains
    • Haemoglobin forms more disulfide bridges with the plasma proteins
    • Haemoglobin dissolves more readily in the blood plasma
    • Haemoglobin molecules stick together to form fibres, distorting red blood cells

  10. Adding a reducing agent breaks the disulfide bridges in a protein. Which structural level is most directly affected?

    • Secondary structure, because the alpha helix is formed by disulfide bridges
    • Tertiary structure, because disulfide bridges help maintain the 3D shape
    • Quaternary structure, because subunits are always joined by disulfide bridges
    • Primary structure, because the amino acid sequence is changed

  11. Heating a protein breaks its hydrogen and ionic bonds. What happens to its structure and function?

    • It denatures, losing its 3D shape and often its function, while the primary sequence is unchanged
    • It gains a larger number of peptide bonds, which strengthens the protein and makes it more functional
    • It forms additional quaternary subunits, which increases its functional activity in the cell membrane
    • It is hydrolysed into separate amino acids, so the primary sequence of the protein is completely destroyed

  12. Which level of structure is most important for the shape of an enzyme's active site?

    • Primary structure alone, because the sequence fixes the active site shape
    • Secondary structure, because it always forms a flat sheet at the active site with no exceptions
    • Tertiary structure, because it determines the shape of the folded active site
    • Quaternary structure, because all enzymes have four polypeptide chains

  13. A protein has three identical polypeptide chains, each with 100 amino acids. How many peptide bonds are present in total?

    • 300
    • 297
    • 303
    • 294

  14. Which description best matches a fibrous protein such as collagen?

    • Compact spherical molecules with a hydrophobic core that binds oxygen
    • Long strands with a regular repeating structure that gives mechanical strength
    • Molecules that are phosphorylated and act as energy carriers in cells
    • Small peptides that are hydrolysed rapidly in the gut to release amino acids with no exceptions

  15. Which level of structure is disrupted when the shape of a protein changes but its amino acid sequence remains the same?

    • Secondary structure only, because no other level is affected by folding
    • Quaternary structure only, because subunits always change shape first
    • Primary structure, because the sequence is altered by the change in shape
    • Tertiary structure, because its folding is changed while the primary sequence is intact

  16. A student claims that the primary structure alone determines a protein's function. Which evaluation is most accurate?

    • Incorrect, because only the quaternary structure of a protein has any effect on whether it can function
    • Incorrect, because the primary structure has no influence whatsoever on the shape that the protein adopts
    • Partly correct, since the primary sequence determines folding, but function also depends on the final 3D and quaternary structure
    • Correct, because the primary structure fully determines the folding of the chain and therefore all of its function

  17. Changing the pH of a protein solution far from its normal range can disrupt its shape. Which interaction is most directly affected?

    • Glycosidic bonds between subunits, because their oxygen atoms are protonated
    • Ionic bonds between charged R groups, because their ionisation state changes
    • Phosphodiester bonds, because the pH alters the sugar-phosphate backbone
    • Peptide bonds in the primary structure, because the pH hydrolyses them

  18. Haemoglobin shows cooperative oxygen binding. Which explanation is most accurate?

    • Oxygen binding removes the quaternary structure, which then increases the rate of binding
    • Binding of oxygen to one subunit changes the shape of the others, making them more likely to bind oxygen
    • Oxygen binding breaks the peptide bonds, allowing the other subunits to bind more oxygen
    • Oxygen forms covalent bonds with each subunit, so each binding is independent

  19. Explain why collagen is strong, using its quaternary structure.

    • Collagen contains many disulfide bridges that link each amino acid in the chain to the next amino acid
    • Three polypeptide chains wind into a triple helix, with many hydrogen bonds between chains that give strength
    • Collagen contains phosphate groups that cross-link its chains together into a rigid three-dimensional lattice
    • Collagen has four identical chains that repel one another strongly, which creates tension in the tissue

  20. Which description accurately links a protein's quaternary structure to its function?

    • Quaternary structure removes the need for peptide bonds, so the protein is more flexible
    • Quaternary structure prevents the protein from folding, so it remains as a linear chain
    • Quaternary structure makes the protein soluble in lipids, so it can cross the membrane
    • Association of subunits can create binding sites and interactions that a single chain cannot provide

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