Anatomy and Physiology 12 · Biology · Lesson 4.1
DNA replication
- Level
- Grade 12
- Reading time
- 14 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Copying the genetic code.
What is DNA replication?
Short answer
DNA replication is the process by which a cell copies its DNA before dividing, so each new cell gets a complete set. The double helix unwinds, and each strand serves as a template while the enzyme DNA polymerase adds complementary nucleotides (A with T, G with C). The result is two identical DNA molecules, each keeping one original strand — called semiconservative replication.
Concept preview
What you will be able to do
- 01Recap the structure of DNA: the double helix, antiparallel strands and complementary base pairing.
- 02Explain what semiconservative replication means and why it produces faithful copies.
- 03Describe the roles of helicase, primase, DNA polymerase and ligase at the replication fork.
- 04Distinguish the leading and lagging strands and explain Okazaki fragments.
- 05Explain how proofreading makes replication extraordinarily accurate.
DNA, deoxyribonucleic acid, is the molecule that carries the instructions for building and running every cell in your body, and its most famous feature is its shape: the double helix, two long strands wound around each other like a spiral staircase. Each strand is a chain of repeating units called nucleotides, and every nucleotide has three parts joined together: a phosphate group, a five-carbon sugar called deoxyribose, and one of four nitrogen-containing bases. The sugars and phosphates link up to form the two long handrails, the sugar-phosphate backbone, while the bases point inward toward the centre to form the flat steps of the staircase. This tidy, repetitive architecture is exactly what makes the molecule so easy to copy.
School Plan
DNA replication
This lesson's full explanation, worked examples, quiz and practice are locked. Full access is on the School Plan.
Log in or start free and you will return right here.
Related topics
Frequently asked questions
- What does "semiconservative" mean?
- Each new DNA molecule keeps one original strand and one newly made strand, so half of each copy is conserved.
- What enzyme builds the new DNA strand?
- DNA polymerase, which adds complementary nucleotides along each template strand.