Explain how the double helix structure of DNA enables the molecule to carry out both storage and transmission of genetic information.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The sequence of bases along a DNA strand encodes genetic information, acting as a genetic code. Complementary base‑pairing (A–T and C–G) between the two strands means each strand can serve as a template for replication. The two strands are held together by hydrogen bonds, which are weak enough to allow strand separation during replication or transcription. The helical, double‑stranded structure protects the base sequence from chemical damage – the sugar–phosphate backbone shields the bases on the outside, contributing to long‑term stable storage of information.
Examiner tips
- Use the exact terms ‘complementary base‑pairing’, ‘hydrogen bonds’, ‘sugar‑phosphate backbone’, and ‘genetic code’.
- Show the logical link: base sequence → information storage; base pairing → template for replication; weak H‑bonds → strand separation; backbone protection → stability.
- Keep the answer concise – 4 points, one sentence per point.
Common mistakes
- Confusing the direction of replication with the direction of the genetic code; writing ‘A–G’ or ‘C–T’ instead of the correct pairs.
- Over‑expanding the answer with irrelevant details such as the role of histones or chromatin structure.
Mark scheme (4 marks)
- The sequence of bases along the DNA strand encodes genetic information / acts as a genetic code.
- Complementary base pairing (A–T and C–G) between the two strands means each strand can serve as a template for replication.
- The two strands are held together by hydrogen bonds, which are weak enough to allow strand separation during replication or transcription.
- The helical / double-stranded structure protects the base sequence from chemical damage / the sugar–phosphate backbone shields the bases on the outside, contributing to long-term stable storage of information.
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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