DNA Replication
DNA copies itself semi-conservatively.
About this topic
DNA replication copies the molecule before cell division. The enzyme helicase unwinds and unzips the helix, exposing template strands; DNA polymerase adds complementary nucleotides to each strand, producing two identical double helices. Each new DNA has one original strand and one new strand: semi-conservative replication, shown by Meselson and Stahl.
Replication takes place in S phase and is highly accurate, with proofreading by polymerase. Errors that escape become mutations.
Replication is described as semi-conservative: each new DNA molecule has one old strand and one new strand. Helicase breaks hydrogen bonds between base pairs, and at each replication fork DNA polymerase builds a new strand only in one direction, so one strand is made continuously and the other in short fragments joined by ligase. Replication begins at many origins at once so that the huge genome is copied in hours.
Polymerase also proofreads, so errors are about one in a billion bases; those that slip through are mutations. The Meselson-Stahl experiment, using heavy nitrogen, proved the semi-conservative model. The lab technique PCR copies DNA in a similar way using heat cycles. Students often forget that replication happens in S phase before mitosis, not during it.
Key ideas
- Helicase unzips the strands
- DNA polymerase adds bases
- Each new molecule has one old strand
Quick check
Use cases: where DNA Replication helps
- Homework: review the key idea behind DNA Replication before you start a problem set.
- Exam revision: use the quick check to test whether you can recall DNA Replication without notes.
- Visual learning: play with the interactive lab to see how DNA Replication changes when you adjust its inputs.
- Teaching a friend: explain DNA Replication in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is DNA Replication?
DNA copies itself semi-conservatively.
What will I learn in DNA Replication?
Helicase unzips the strands. DNA polymerase adds bases. Each new molecule has one old strand.
Is DNA Replication part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the DNA Replication lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study DNA Replication?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.