Lesson 2.2.1

2.2.1 Nucleotides, DNA and RNA structure Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 2

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 2.2.1, Nucleotides, DNA and RNA structure: 20 multiple choice questions for the Pearson Edexcel Biology A (Salters-Nuffield) (9BI0), Unit 2: Genes and Health, written with Revision Ninja.

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The 20 questions

  1. What are the three components of a nucleotide?

    • A pentose sugar, a phosphate group and a nitrogenous base
    • A glycerol molecule, a phosphate group and a fatty acid
    • An amino acid, a phosphate group and a hydroxyl group
    • A glucose molecule, a sulfur atom and a nitrogenous base

  2. Which sugar is found in DNA nucleotides?

    • Ribose
    • Fructose
    • Deoxyribose
    • Glucose

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

    • Uracil
    • Guanine
    • Cytosine
    • Thymine

  4. Which bases are purines?

    • Uracil and cytosine
    • Thymine and cytosine
    • Adenine and thymine
    • Adenine and guanine

  5. Which bases are pyrimidines?

    • Adenine and guanine, both single-ring bases found in DNA and RNA
    • Cytosine, thymine and uracil
    • Adenine and uracil, both single-ring bases that pair with thymine in DNA
    • Guanine and thymine, both single-ring bases that pair with cytosine in DNA

  6. What type of bond links adjacent nucleotides in a DNA strand?

    • Phosphodiester bond, formed by condensation between the phosphate and the sugar of the next nucleotide
    • Glycosidic bond, formed by hydrolysis between two pentose sugars that are linked in the strand backbone
    • Peptide bond, formed by condensation between the amine group of one amino acid and the carboxyl group of another
    • Hydrogen bond, formed between the phosphate groups of adjacent nucleotides along the sugar-phosphate backbone of the strand

  7. Which base pairs with adenine in DNA, and how many hydrogen bonds form between them?

    • Thymine, with two hydrogen bonds
    • Guanine, with three hydrogen bonds
    • Cytosine, with two hydrogen bonds
    • Thymine, with three hydrogen bonds

  8. In a DNA molecule, the proportion of adenine is 30%. What is the proportion of guanine?

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

  9. A DNA double helix contains 10 A-T base pairs and 5 G-C base pairs. How many hydrogen bonds hold the two strands together?

    • 35
    • 40
    • 30
    • 25

  10. Which description of the two strands of a DNA double helix is correct?

    • They run antiparallel, so one runs 5' to 3' and the other runs 3' to 5'
    • They are joined by peptide bonds between the bases on opposite strands
    • They are joined by covalent phosphodiester bonds between the two strands
    • They run parallel, so both strands run 5' to 3' in the same direction

  11. What is the structural difference between a DNA nucleotide and an RNA nucleotide?

    • DNA contains glucose and cytosine, whereas RNA contains fructose and guanine
    • DNA contains ribose and thymine, whereas RNA contains deoxyribose and uracil
    • DNA contains ribose and uracil, whereas RNA contains deoxyribose and thymine
    • DNA contains deoxyribose and thymine, whereas RNA contains ribose and uracil

  12. Why is RNA generally single-stranded while DNA is double-stranded?

    • RNA lacks any bases, so it cannot pair with another strand under any conditions in cells
    • DNA is single-stranded only in mitochondria, whereas RNA is double-stranded in the nucleus
    • RNA is usually made as a single copy that folds on itself, whereas DNA pairs with a complementary strand
    • RNA is double-stranded because it contains uracil, which forms more hydrogen bonds than thymine

  13. A short DNA strand has the sequence 5'-ATGC-3'. What is the sequence of the complementary strand written 5' to 3'?

    • ATGC
    • GCAT
    • CGTA
    • TACG

  14. Which feature of DNA allows it to be copied accurately during replication?

    • The short length of each strand, which means that copying is unlikely to make errors
    • Complementary base pairing, so each strand can act as a template for a new strand
    • The presence of uracil in every nucleotide, which prevents the strands from separating
    • The presence of amino acids in each strand, which stabilises the sequence

  15. Why is the DNA double helix stable despite being made of two strands held together by weak hydrogen bonds?

    • The strands are joined by glycosidic bonds, which are stronger than phosphodiester bonds
    • The hydrogen bonds are covalent, so they cannot be broken easily under normal conditions
    • Many hydrogen bonds form along the length of the helix, and base stacking adds stability
    • The helix is held together by peptide bonds, which are very strong in the cell environment

  16. What does the term phosphodiester bond describe?

    • A bond between two bases on opposite strands of the double helix
    • A bond between the phosphate group of one nucleotide and the sugar of the next nucleotide
    • A bond between two fatty acids and a glycerol backbone in a triglyceride
    • A bond between two amino acids in a polypeptide chain

  17. A student extracts DNA from a sample and finds that the proportion of cytosine is 18%. What proportion of thymine is expected?

    • 32%
    • 64%
    • 18%
    • 50%

  18. Which of these best describes a nucleoside?

    • A pentose sugar joined to a nitrogenous base, without a phosphate group
    • A nitrogenous base joined to a phosphate group, without a sugar
    • A chain of several nucleotides joined by hydrogen bonds
    • A pentose sugar joined to a phosphate group, without a base

  19. Why is the base sequence of DNA important for an organism?

    • It determines the number of hydrogen bonds in the strand, which sets the rate of respiration
    • It determines the proportion of water in the nucleus, which affects the activity of enzymes
    • It determines the size of the cell, because each base codes for a fixed number of cells
    • It determines the sequence of amino acids in proteins through the genetic code

  20. A DNA sample contains 200 nucleotides in total. Each nucleotide has a mass of about 330 daltons. What is the approximate mass of the sample?

    • 660 daltons
    • 330 000 daltons
    • 6600 daltons
    • 66 000 daltons

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