Lesson 3.1.4.1.3

3.1.4.1.3 Bonds in protein structure and the biuret test: AQA Biology, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.1.4.1.3, Bonds in protein structure and the biuret test: 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. Which solution is added to sodium hydroxide in the biuret test?

    • Copper(II) sulfate
    • Iron(II) sulfate
    • Sodium chloride
    • Potassium iodide

  2. What colour change indicates a positive result in the biuret test?

    • Blue to brick-red
    • Blue to purple
    • Yellow to blue-black
    • Clear to cloudy

  3. What does the biuret test detect?

    • Ester bonds
    • Phosphodiester bonds
    • Peptide bonds
    • Glycosidic bonds

  4. What colour is a negative result in the biuret test?

    • Blue
    • Brick-red
    • Blue-black
    • Purple

  5. Which bond is the weakest of those that stabilise protein tertiary structure?

    • Hydrogen bond
    • Peptide bond
    • Disulfide bridge
    • Ionic bond

  6. Between which groups do ionic bonds form in a protein tertiary structure?

    • Adjacent carboxyl groups
    • Uncharged amino acids
    • Oppositely charged R-groups
    • Adjacent peptide bonds

  7. Which amino acid contributes the sulfur atoms that form disulfide bridges?

    • Alanine
    • Glycine
    • Cysteine
    • Serine

  8. Which chemical bond produces a positive purple result in the biuret test?

    • Glycosidic bond
    • Ester bond
    • Peptide bond
    • Phosphodiester bond

  9. What is the minimum number of peptide bonds needed for a positive biuret test?

    • Two
    • One
    • Three
    • Four

  10. Why does a glucose solution give a negative result in the biuret test?

    • Lacks ester bonds
    • Lacks reducing sugars
    • Lacks peptide bonds
    • Lacks glycosidic bonds

  11. A colorimeter reading of biuret-treated protein standards is 0.8 at 2 mg/cm3 and 1.6 at 4 mg/cm3. An unknown gives 1.2. What is the protein concentration?

    • 6 mg/cm3
    • 2.4 mg/cm3
    • 2 mg/cm3
    • 3 mg/cm3

  12. How many peptide bonds are present in a linear pentapeptide molecule?

    • Four
    • Three
    • Five
    • Six

  13. Where do non-polar R-groups cluster within a globular protein in water?

    • Peptide backbone
    • Active site
    • Protein interior
    • Protein surface

  14. Why can the biuret test not prove a sample contains only protein?

    • It detects carbohydrates
    • It is qualitative
    • It requires heating
    • It destroys proteins

  15. Why do individual free amino acids give a negative biuret test result?

    • No carboxyl groups
    • No amine groups
    • No peptide bonds
    • No carbon atoms

  16. Which condition is required for copper(II) ions to form a purple biuret complex?

    • Boiling water
    • Alkaline pH
    • Acidic pH
    • High temperature

  17. Which type of bond maintains the primary structure of a protein during heating?

    • Disulfide bridges
    • Ionic bonds
    • Hydrogen bonds
    • Peptide bonds

  18. What does a pale lilac biuret result indicate compared to a dark purple one?

    • Higher protein concentration
    • Lower protein concentration
    • Absence of bonds
    • Presence of lipids

  19. What effect does a change in pH have on protein ionic bonds?

    • Breaks disulfide bridges
    • Hydrolyses peptide bonds
    • Alters R-group charge
    • Denatures primary structure

  20. What level of protein structure is directly detected by the biuret test?

    • Primary structure
    • Quaternary structure
    • Tertiary structure
    • Secondary structure

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