A1.2.6—DNA as a double helix
DNA forms a double helix from two antiparallel polynucleotide strands held together by hydrogen bonds between complementary bases in the molecule.
- Syllabus
- First assessment 2025
- Objective
- A1.2.6
- Level
- HL
Exam analysis
Chance of appearing12%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1–2
Common command terms
- Describe
- Explain
- Deduce
- Draw
- Sketch
Scoring notes
- Common mistake
- Mixing up covalent sugar-phosphate bonds with hydrogen bonds between complementary bases.
Recent exam appearances
November 2025Paper1A HL · TZ31[ 1 ]A1.2.6—DNA as a double helix
November 2024Paper1 HL · TZ08[ 1 ]A1.2.6—DNA as a double helix
May 2024Paper1 HL · TZ19[ 1 ]A1.2.6—DNA as a double helix
May 2023Paper1 HL · TZ125[ 1 ]A1.2.6—DNA as a double helix
May 2023Paper1 HL · TZ222[ 1 ]A1.2.6—DNA as a double helix
Practice this objective
Coverage 2013–2025 · Updated 14 Jul 2026
Concept essentials
- DNA as a double helix should be described using precise molecular vocabulary.
- Structure and information must be kept separate: backbones provide continuity while bases carry sequence meaning.
- Exam answers should match the command term and avoid adding unsupported extra claims.