# Explain how complementary base pairing in DNA contributes to both the accurate storage and the faithful transmission of genetic information.

> IB DP Biology Higher Level (2023 syllabus) — A1.2 Nucleic acids · Explain · 4 marks

## Mark scheme (4 marks)

1. 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.
2. 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.
3. 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.
4. 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

- [complementary base pairing](https://www.gradenine.co.uk/glossary/complementary-base-pairing)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-complementary-base-pairing-in-87ac8a72) · Published by Druglandscape Ltd.