Lesson 3.3.13.4

3.3.13.4 DNA Quiz: AQA Chemistry, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.3.13.4, DNA: 20 multiple choice questions for the AQA Chemistry (7405), Unit 3: Organic chemistry, written with Revision Ninja.

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The 20 questions

  1. What three components make up a nucleotide in DNA?

    • Glucose, phosphate and an amino acid
    • A phosphate group, 2-deoxyribose and a base
    • Ribose, uracil and a lipid
    • A phosphate, a fatty acid and a base

  2. Which base is NOT found in DNA?

    • Thymine
    • Cytosine
    • Guanine
    • Uracil

  3. What type of sugar is 2-deoxyribose in DNA?

    • A disaccharide
    • A pentose sugar
    • A hexose sugar
    • A triose sugar

  4. How are nucleotides joined together in a DNA strand?

    • By ionic bonds between phosphate groups, which link each nucleotide to the next one
    • By covalent bonds between the phosphate of one nucleotide and the sugar of the next
    • By peptide links between the sugars, which join the nucleotides into a polymer
    • By hydrogen bonds between the bases of one strand only, which hold the chain together

  5. How many strands make up a DNA double helix?

    • One
    • Two
    • Four
    • Three

  6. How many hydrogen bonds form between adenine and thymine?

    • 1
    • 2
    • 3
    • 4

  7. Which base pair forms three hydrogen bonds?

    • Guanine and cytosine
    • Thymine and cytosine
    • Adenine and thymine
    • Adenine and guanine

  8. If one DNA strand reads A-T-G-C, what is the sequence of the complementary strand?

    • A-T-G-C
    • T-A-C-G
    • G-C-T-A
    • C-G-A-T

  9. Why does adenine pair only with thymine in DNA?

    • The complementary shapes allow two hydrogen bonds to form between them
    • Adenine and thymine are both purines, so they fit together in the double helix
    • Adenine has a triple bond to thymine, which makes the pair much stronger than others
    • Thymine contains an ester group that bonds to adenine and holds the pair together

  10. Which bond links the phosphate and sugar units in a DNA backbone?

    • Hydrogen bonds only between the sugar and the base of each nucleotide in the chain
    • Metallic bonds between the sugar units, which hold the chain together in the helix
    • Ionic bonds between the phosphate groups, which hold the backbone together in solution
    • Covalent (phosphodiester) bonds

  11. If 30% of one DNA strand is adenine, what percentage of thymine is in the complementary strand?

    • 60%
    • 70%
    • 30%
    • 20%

  12. What gives DNA its overall negative charge?

    • The base pairs
    • The phosphate groups in the backbone
    • The deoxyribose sugar units
    • The hydrogen bonds between strands

  13. Why does the separation of DNA strands allow replication?

    • Separated strands form ionic bonds with each other, which then rejoin them after copying
    • Replication depends on the strands forming peptide links between the bases of each pair
    • The strands are identical, so no new copy is needed because the original can be reused
    • Each strand can act as a template for a new complementary strand because of base pairing

  14. Why is the DNA double helix stabilised?

    • Hydrogen bonds between base pairs and stacking between bases
    • Disulfide bonds between phosphate groups, which link the two backbones in the helix
    • Peptide links between sugar units, which hold the two strands together in the helix
    • Metallic bonds between the two strands, which hold the helix together in solution

  15. Which statement about a single DNA strand is correct?

    • It is a double helix held by peptide links between the bases of its two strands
    • It is a polymer of nucleotides with bases attached to the sugars in the chain
    • It has no bases attached to the sugar units, so it has no genetic information
    • It contains only amino acids linked by peptide bonds, forming a polypeptide chain

  16. How many hydrogen bonds are present in 10 A-T base pairs?

    • 40
    • 20
    • 30
    • 10

  17. What is broken when DNA strands separate, as in denaturation by heating?

    • The covalent bonds in the sugar-phosphate backbone
    • The hydrogen bonds between base pairs
    • The C-C bonds in the sugar
    • The peptide links joining the bases

  18. Which component of a nucleotide carries the base attachment?

    • The phosphate group
    • The carboxylic acid group
    • The amino group
    • The deoxyribose sugar

  19. Why do A-T rich regions of DNA separate more easily than G-C rich regions when heated?

    • A-T pairs have only two hydrogen bonds, compared with three for G-C pairs
    • G-C pairs have no hydrogen bonds, so they separate more easily when heated
    • A-T pairs have a higher molar mass, so they require more energy to separate
    • A-T pairs contain covalent bonds that are weaker than the bonds in G-C pairs

  20. Which bases are purines?

    • Guanine and thymine
    • Adenine and guanine
    • Adenine and cytosine
    • Thymine and cytosine

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