Semi-conservative replication
DNA copies itself by unzipping. Each old strand is used as a template for a new strand, so every new double helix has one old and one new strand.
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Analogy
Photocopying a double-sided page by splitting it and copying each side.
In practice
Helicase unwinds the helix. DNA polymerase adds matching nucleotides to the new strand.
Practice
Flashcards
- Why is DNA replication called semi-conservative?Each new double helix keeps one original strand and gets one new strand.
Interview questions
- Describe the steps of DNA replication and explain why it is called semi-conservative.
- Helicase unwinds and separates strands
- Primase starts a primer
- DNA polymerase adds nucleotides 5' to 3'
- Leading continuous, lagging in Okazaki fragments
- Each helix has one old and one new strand
Questions people ask
Who proved DNA replication is semi-conservative?
Meselson and Stahl showed it in 1958. They grew bacteria in heavy nitrogen, then moved them to light nitrogen and tracked the DNA density. After one round the DNA was of medium density, matching one old and one new strand. This ruled out the idea of a fully conserved copy.
How accurate is DNA replication?
Very accurate. DNA polymerase picks the wrong base roughly once in 100,000 bases, but it can proofread and correct most of these mistakes. Repair systems fix others afterwards. In the end, only about one error in a billion bases survives, so most daughter cells have nearly identical genomes.