Explain how the structure of a DNA nucleotide relates to its function in storing genetic information.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
DNA is a polymer made from nucleotide monomers. The sequence of bases in DNA acts as a code for the sequence of amino acids in a protein.
Model answer (5 marks)
1. A DNA nucleotide consists of a deoxyribose sugar, a phosphate group and a nitrogenous base.
2. The four bases are adenine, thymine, cytosine and guanine.
3. The linear sequence of these bases forms a code that determines the sequence of amino acids in a protein.
4. Bases pair specifically – A with T and C with G – which stabilises the double‑stranded structure.
5. The double‑helix with complementary base pairing allows accurate replication of the genetic information during cell division.
2. The four bases are adenine, thymine, cytosine and guanine.
3. The linear sequence of these bases forms a code that determines the sequence of amino acids in a protein.
4. Bases pair specifically – A with T and C with G – which stabilises the double‑stranded structure.
5. The double‑helix with complementary base pairing allows accurate replication of the genetic information during cell division.
Examiner tips
- Use the exact terms – deoxyribose, phosphate, base; A‑T, C‑G; double helix; replication.
- Show the link between base sequence and protein coding.
- Mention complementary base pairing as the basis for accurate copying.
- Keep each point concise and directly tied to the marks scheme.
Common mistakes
- Confusing ribose with deoxyribose; writing RNA bases (U) instead of DNA bases.
- Failing to mention the complementary base pairing or the double‑helix structure.
- Giving extra information not asked, such as transcription or translation details.
Mark scheme (5 marks)
- A DNA nucleotide contains a deoxyribose sugar, a phosphate group, and a (nitrogenous) base
- There are four different bases (adenine, thymine, cytosine, guanine) in DNA
- The sequence / order of bases acts as a code / carries the genetic information / instructions for making proteins
- Bases pair specifically / complementary base pairing (A with T, C with G) holds the two strands together
- The double-stranded / double helix structure with complementary base pairing allows accurate copying / replication of genetic information
Key terms in this question
Related
- All AQA A-Level Biology (7402) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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