Lesson 3.1.5.1.1

3.1.5.1.1 Nucleotides and the structure of DNA and RNA Quiz: AQA Biology, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

In partnership with Revision Ninja

Lesson 3.1.5.1.1, Nucleotides and the structure of DNA and RNA: 20 multiple choice questions for the AQA Biology (7402), Unit 1: Biological molecules, written with Revision Ninja.

Host it live on the board and students join with a game code on their own devices, or revise alone with Free Play. The answers are revealed in the game.

Host this setFree Play

The 20 questions

  1. Which three components make up a nucleotide?

    • A hexose sugar, a phosphate group and a fatty acid chain that together form a glycerolipid molecule
    • A pentose sugar, an amino group and a carboxyl group that together form a single amino acid unit
    • A pentose sugar, a phosphate group and a nitrogen-containing organic base
    • A glycerol backbone, a phosphate group and a peptide bond that together form a phospholipid molecule

  2. Which pentose sugar is found in DNA nucleotides?

    • Deoxyribose
    • Fructose
    • Ribose
    • Glucose

  3. Which base is found in RNA but not in DNA?

    • Adenine
    • Thymine
    • Uracil
    • Guanine

  4. Which bond joins adjacent nucleotides in a polynucleotide chain?

    • Peptide bond formed by condensation between two amino acids
    • Phosphodiester bond
    • Glycosidic bond
    • Hydrogen bond between two complementary bases

  5. Which base pairs are complementary in DNA?

    • Adenine with uracil, and thymine with guanine
    • Adenine with thymine, and cytosine with guanine
    • Adenine with guanine, and cytosine with thymine
    • Adenine with cytosine, and guanine with thymine

  6. How many hydrogen bonds form between cytosine and guanine?

    • 4
    • 3
    • 2
    • 1

  7. Which description best matches an RNA molecule?

    • A ring of glucose units joined by glycosidic bonds
    • A double helix of two long polynucleotide chains
    • A relatively short single polynucleotide chain
    • A chain of amino acids joined by peptide bonds

  8. In a DNA sample, 30% of the bases are adenine. What percentage of the bases are guanine?

    • 20%
    • 70%
    • 40%
    • 30%

  9. A DNA molecule contains 100 A-T base pairs and 50 C-G base pairs. How many hydrogen bonds hold the base pairs together?

    • 300
    • 400
    • 250
    • 350

  10. A DNA double helix is made of two strands each of 1000 nucleotides. How many phosphodiester bonds are present in total?

    • 1999
    • 2000
    • 1998
    • 1996

  11. Which of these bases is a purine, with a double-ring structure?

    • Guanine
    • Uracil
    • Thymine
    • Cytosine

  12. Which base pairs with adenine in RNA?

    • Uracil
    • Cytosine
    • Guanine
    • Thymine

  13. What structural difference separates ribose from deoxyribose?

    • Deoxyribose contains a nitrogen atom within its ring, which is absent from the ribose ring
    • Deoxyribose has a six-carbon ring rather than the five-carbon ring that is found in ribose
    • Deoxyribose has an extra phosphate group attached to carbon 1 of the sugar ring structure
    • Deoxyribose lacks an oxygen atom on carbon 2, having a hydrogen atom there instead

  14. What does the term double helix describe in the structure of DNA?

    • A single polynucleotide chain folded back on itself into a closed ring of linked nucleotides
    • A chain of glucose units coiled into a spiral shape by glycosidic bonds between the sugar units
    • Two polypeptide chains joined together by disulfide bridges between cysteine residues in the chain
    • Two polynucleotide chains wound around each other and held together by base-pair hydrogen bonds

  15. A DNA molecule has 20% cytosine among 3000 total bases. How many guanine bases are present?

    • 300
    • 600
    • 1200
    • 900

  16. Evaluate the claim that because DNA has only four bases, it cannot carry enough information to encode the complexity of an organism.

    • The claim is not sound, because information is held in the sequence of many bases in a long chain, not in the number of base types
    • The claim is sound, because four bases can only encode four different traits, so DNA could carry little information
    • The claim is sound, because DNA is far too simple a molecule to be the basis of inheritance, given its few bases
    • The claim is not sound, because proteins carry most of the genetic information instead of DNA, which only regulates them

  17. Explain why the double helix of DNA is stable, given that it is held together by hydrogen bonds between base pairs.

    • Each hydrogen bond is strong and covalent, so a single bond between two bases is enough to hold the whole helix firmly
    • Many hydrogen bonds form along the helix and stacked bases add stability, so the combined interactions hold the strands firmly
    • The phosphate groups form ionic bonds with the bases on the opposite strand, locking the two strands together along the helix
    • The double helix is held together by peptide bonds between the paired bases, which link the two strands at every base pair

  18. Explain why an mRNA molecule is single-stranded and relatively short, in relation to its function.

    • It is short because it must be stored in the nucleus indefinitely in order to protect the genes from damage
    • It is single-stranded because it binds to proteins only, so the strand is folded tightly to fit into the protein complex
    • It is single-stranded because uracil cannot pair with any other base in the cell, so only one strand can form
    • It carries a copy of a gene's sequence from the nucleus to ribosomes, so a short single strand is sufficient and can be read directly

  19. Explain why DNA is more stable than RNA in the cell, relating the difference to the structure of the sugar.

    • Ribose forms peptide bonds with the bases that make RNA more easily digested in the cytoplasm than DNA
    • Deoxyribose lacks the hydroxyl group on carbon 2, so DNA is less susceptible to hydrolysis than RNA
    • Ribose contains more phosphate groups than deoxyribose, which makes RNA chemically less stable in the cell
    • Deoxyribose contains a double bond that makes DNA less reactive with water in the cytoplasm of cells

  20. A DNA sample is found to have 40% thymine. Which conclusion about this sample is correct?

    • It is RNA, because thymine is found only in RNA molecules and never in double-stranded DNA
    • It has 40% cytosine and 60% guanine, since the bases in DNA are not paired in equal proportions
    • It has 60% cytosine and 40% guanine, because the thymine content determines the guanine content
    • It has 10% cytosine and 10% guanine, assuming it is double-stranded DNA

All AQA Biology quizzes