Replication
ScienceDefinition
DNA replication is the biological process by which a cell copies its entire DNA before cell division, ensuring each daughter cell receives an identical set of genetic instructions. It is semi-conservative, meaning each new DNA molecule contains one original strand and one newly synthesized strand.
How It Works
- Helicase unwinds and separates the double helix at the origin of replication, creating a replication fork.
- Single-strand binding proteins stabilize the separated strands to prevent them from re-annealing.
- Primase synthesizes short RNA primers on each template strand.
- DNA polymerase III adds complementary nucleotides to the primers, building the new strand in the 5' to 3' direction.
- The leading strand is synthesized continuously; the lagging strand is made in short Okazaki fragments.
- DNA polymerase I replaces RNA primers with DNA, and DNA ligase seals the gaps between fragments.
Examples
- Every human cell copying all 6 billion base pairs before mitosis
- Bacteria replicating their circular chromosome before binary fission
- PCR in a lab mimicking replication to amplify DNA samples
Key Fact
Replication is semi-conservative (Meselson-Stahl experiment, 1958); DNA polymerase adds nucleotides only 5'→3'
Study This Concept
Practice replication with free review games in these units: