D1.2.12 (HL)—Directionality
Directionality in gene expression means RNA is synthesized and mRNA is translated in defined 5 prime to 3 prime directions during synthesis.
- Syllabus
- First assessment 2025
- Objective
- D1.2.12
- Level
- HL
Exam analysis
Chance of appearing2%of analysed past papers
Latest appearanceNovember 2023
Most common paperPaper1
Typical marks1
Common command terms
- Identify
Scoring notes
- Common mistake
- Choosing a start codon without using the 5 prime to 3 prime direction shown in the diagram.
Recent exam appearances
November 2023Paper3 ["HL"] · TZ23(c)[ 1 ]D1.2.12 (HL)—Directionality
May 2021Paper1 ["HL"] · TZ227[ 1 ]D1.2.12 (HL)—Directionality
Practice this objective
Coverage 2021–2023 · Updated 16 Jul 2026
Concept essentials
- RNA synthesis proceeds in the 5 prime to 3 prime direction.
- The ribosome reads mRNA codons from 5 prime to 3 prime.
- Start codon position is interpreted using mRNA direction.
- Template and product strands have opposite orientations during transcription.