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D1.1.7 (HL)—Leading vs. lagging strand

Leading versus lagging strand explains how DNA is copied, checked, amplified or analysed through specific strand relationships, enzymes and molecular techniques.

Syllabus
First assessment 2025
Objective
D1.1.7
Level
HL

Exam analysis

Chance of appearing2%of analysed past papers
Latest appearanceNovember 2024
Most common paperPaper1
Typical marks1

Common command terms

  • Identify

Scoring notes

Common mistake
Saying both strands are copied continuously instead of identifying discontinuous lagging-strand synthesis.

Recent exam appearances

November 2024Paper1 ["HL"] · TZ026[ 1 ]D1.1.7 (HL)—Leading vs. lagging strand
May 2022Paper1 ["HL"] · TZ126[ 1 ]D1.1.7 (HL)—Leading vs. lagging strand
Practice this objective

Coverage 2022–2024 · Updated 16 Jul 2026

Concept essentials

  • Leading versus lagging strand depends on matching each strand, enzyme or laboratory step to its exact function.
  • Template strands and complementary base pairing give leading versus lagging strand its copying accuracy.
  • Leading versus lagging strand is clearer when amplification, separation and profiling are not confused.
  • Molecular evidence for leading versus lagging strand must be interpreted from bands, isotopes, primers or enzyme roles.
ConceptIB Biology HL