Lesson 18B.4

18B.4 Proteins and the peptide bond Quiz: Pearson Edexcel Chemistry, Unit 18

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 18B.4, Proteins and the peptide bond: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 18: Organic Chemistry III, written with Revision Ninja.

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The 20 questions

  1. Which reaction forms a peptide bond?

    • Addition, in which amino acids combine across a double bond with no atoms lost in the process at all
    • Hydrolysis, in which water breaks a carbon-carbon bond between two residues and releases both of them
    • Condensation, in which an amine group of one amino acid reacts with a carboxylic acid of another, losing water
    • Oxidation, in which a carboxylic acid is converted to an aldehyde by loss of hydrogen from the chain

  2. What are the products of complete hydrolysis of a protein?

    • Its constituent amino acids
    • Nucleotides and phosphate ions
    • Glucose and fatty acids
    • Ethanoic acid and ammonia

  3. Which reagent is commonly used to hydrolyse a protein into amino acids?

    • Bromine water under UV light
    • Hot aqueous acid, such as hydrochloric acid
    • Lithium tetrahydridoaluminate in dry ether
    • Cold water with no catalyst

  4. What is the primary structure of a protein?

    • The arrangement of the chains into a sheet pattern
    • The sequence of amino acids joined by peptide bonds
    • The folding of several chains held together by disulfide bridges
    • The coiling of the chain into a helix held by hydrogen bonds

  5. Which functional group is present in a peptide bond?

    • An ester, -COO-
    • A carboxylic acid, -COOH
    • An ether, -O-
    • An amide, -CONH-

  6. How many amino acids are released when a dipeptide is completely hydrolysed?

    • 1
    • 2
    • 3
    • 4

  7. Which amino acids are released when the dipeptide glycine-alanine is hydrolysed?

    • Glycine and alanine
    • Glycine and ethanoic acid
    • Glycine and alanine, plus carbon dioxide only
    • Alanine and ammonia only

  8. How many peptide bonds are in a tetrapeptide?

    • 2
    • 4
    • 1
    • 3

  9. How many moles of water are consumed in complete hydrolysis of 1 mol of a tripeptide?

    • 2 mol, which is 36 g
    • 3 mol, which is 54 g
    • 1 mol, which is 18 g
    • 4 mol, which is 72 g

  10. Why is glycine not optically active?

    • It has two carboxylic acid groups, so it is achiral
    • Its alpha carbon has two hydrogen atoms, so it is not chiral
    • It has a benzene ring, which makes it optically inactive
    • It has no amine group, so it cannot be chiral

  11. Which statement about amino acids in aqueous solution at neutral pH is correct?

    • All amino acids can exist as zwitterions, since they have both an acidic and a basic group
    • Only glycine forms a zwitterion, since it is the simplest amino acid
    • Only aromatic amino acids form zwitterions, since they are the only ones with charges
    • No amino acid forms a zwitterion, since zwitterions form only in strongly acidic solution

  12. Why is the peptide C-N bond described as partly double-bond in character?

    • The bond is a pure single bond with no electron sharing between the nitrogen and the carbonyl carbon
    • The bond is ionic, with a complete transfer of electrons from nitrogen to carbon in the link
    • The bond contains a triple bond, which is the strongest type of bond and so cannot rotate in the chain
    • Delocalisation of the nitrogen lone pair into the C=O group gives partial double-bond character

  13. Why is the primary structure of a protein important?

    • It determines only the molar mass of the protein, not any other property of the folded molecule
    • It determines the colour of the protein in solution, which depends on the sequence of the amino acids
    • It determines the number of water molecules that the protein holds in its folded structure
    • It determines the amino acid sequence, which controls how the chain folds and its properties

  14. What is the number of amino acid residues in a chain with 150 peptide bonds?

    • 151
    • 300
    • 75
    • 150

  15. A pentapeptide is completely hydrolysed. How many water molecules are needed?

    • 10
    • 5
    • 3
    • 4

  16. Which description best matches a peptide?

    • A cyclic molecule of nitrile groups bonded to carbon
    • A single amino acid with an amide group attached
    • A polymer of only glycine residues, linked by ester groups
    • A short chain of amino acids joined by peptide bonds

  17. Why does hydrolysis of a protein require heating with acid for a long time?

    • Long heating is needed only to make the amino acids visible in the solution for later detection
    • Acid is needed to remove the amine groups before hydrolysis, which then releases the amino acids
    • The peptide bond is ionic and dissolves only in hot acid, so the chain breaks apart completely
    • The peptide bond is strong and resistant to hydrolysis, so harsh conditions are needed

  18. Why can a protein lose its shape when heated?

    • Heat breaks the hydrogen bonds and other interactions that hold the folded shape, without breaking the peptide bonds
    • Heat breaks the peptide bonds, releasing the free amino acids that then form new bonds with water
    • Heat evaporates the amino acids from the protein chain, leaving behind a shorter chain of residues
    • Heat converts the peptide bonds into ester links, which change the shape of the chain permanently

  19. Which bond is broken when a peptide is hydrolysed by acid?

    • The N-H bond of the amine group
    • The O-H bond of the carboxyl group
    • The C=O bond of the carbonyl group
    • The C-N bond of the amide link

  20. What is the name for one amino acid unit within a protein chain?

    • An isotope of the amino acid
    • A monomer with a carbon-carbon double bond
    • A zwitterion with two charges
    • A residue

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