Explain how complementary base pairing in DNA contributes to both the accurate storage and the faithful transmission of genetic information.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Adenine pairs only with thymine and cytosine only with guanine through specific hydrogen bonds, so the base sequence of one strand determines the sequence of the other strand.
During replication each strand acts as a template; complementary base pairing ensures the new strand is an exact copy, preserving the genetic information.
The specificity of base pairing makes mismatches rare, and proofreading/repair mechanisms can detect and correct errors, maintaining the integrity of stored information.
The two complementary strands are held together by hydrogen bonds, giving the double helix stability for long‑term storage while allowing the strands to separate during replication or transcription.
During replication each strand acts as a template; complementary base pairing ensures the new strand is an exact copy, preserving the genetic information.
The specificity of base pairing makes mismatches rare, and proofreading/repair mechanisms can detect and correct errors, maintaining the integrity of stored information.
The two complementary strands are held together by hydrogen bonds, giving the double helix stability for long‑term storage while allowing the strands to separate during replication or transcription.
Examiner tips
- Use the exact base‑pairing pairs (A‑T, C‑G) and mention hydrogen bonds; link each point to the marks scheme.
- Show how template strands lead to faithful copying and error correction.
- Mention stability and strand separation as separate points.
Common mistakes
- Confusing A‑C or G‑T pairs; not specifying hydrogen bonds; omitting the role of proofreading/repair mechanisms.
Mark scheme (4 marks)
- Adenine pairs only with thymine (and cytosine only with guanine) via specific hydrogen bonds, meaning the base sequence of one strand determines the sequence of the other strand.
- During DNA replication each strand acts as a template, and complementary base pairing ensures that the new strand produced is an exact copy of the original, preserving the genetic information.
- The specificity of base pairing means that errors (mismatched bases) are rare and can be detected and corrected by proofreading/repair mechanisms, maintaining the integrity of stored information.
- The two complementary strands are held together by hydrogen bonds between bases, making the double helix stable for long-term storage of information, yet the bonds are individually weak enough to allow strand separation during replication or transcription.
Key terms in this question
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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