AQA GCSE Biology

DNA structure

AQA GCSE Biology revision on DNA structure. Aligned to the AQA GCSE Biology 8461 specification. This bank has 25 practice questions on this topic.

Sample questions (3 of 25)

  1. Question 1

    Which component of a DNA nucleotide forms the backbone of the double helix?

    • A) Nitrogenous base pair
    • B) Phosphate and sugar
    • C) Amino acid sequence
    • D) Hydrogen bond links
    Show answer

    Answer: Phosphate and sugar

    Each nucleotide consists of a phosphate group, a deoxyribose sugar, and a base. The phosphate of one nucleotide bonds to the sugar of the next to form the repeating sugar-phosphate backbone, while the bases project inward.

  2. Question 2

    Which term describes the specific pairing arrangement of nitrogenous bases in DNA?

    • A) Random base pairing
    • B) Complementary pairing
    • C) Double helix pairing
    • D) Nucleotide matching
    Show answer

    Answer: Complementary pairing

    Adenine always pairs with thymine, and cytosine always pairs with guanine. This predictable interaction is known as complementary base pairing, which ensures the genetic code is copied accurately during replication.

  3. Question 3

    What type of chemical bond holds the two strands of the DNA double helix together?

    • A) Strong covalent bonds
    • B) Weak hydrogen bonds
    • C) Ionic mineral bonds
    • D) Carbon peptide links
    Show answer

    Answer: Weak hydrogen bonds

    The two strands of DNA are held together by hydrogen bonds between the complementary base pairs. These bonds are weak, allowing the strands to separate easily for transcription or replication while keeping the overall structure stable.

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