Dna replication
ScienceDefinition
DNA replication is the biological process by which a cell copies its entire DNA molecule before cell division, ensuring each daughter cell receives an identical set of genetic instructions. It is semi-conservative, meaning each new double helix contains one original strand and one newly synthesized strand.
How It Works
- Helicase unwinds and separates the two strands of the double helix at the replication fork.
- Single-strand binding proteins stabilize the separated strands to prevent them from re-annealing.
- Primase synthesizes a short RNA primer on each template strand to provide a starting point.
- DNA polymerase III adds complementary nucleotides to each template strand in the 5' to 3' direction.
- The leading strand is synthesized continuously, while the lagging strand is made in short Okazaki fragments.
- DNA ligase joins the Okazaki fragments on the lagging strand to create a continuous strand.
- The result is two identical double-stranded DNA molecules, each with one old and one new strand.
Examples
- Every time a human cell divides, all 6 billion base pairs of DNA must be replicated
- PCR (polymerase chain reaction) in forensic labs mimics DNA replication to amplify tiny DNA samples
- Errors in replication that escape proofreading can cause mutations leading to genetic diseases
Key Fact
Replication is semi-conservative; human DNA polymerase adds ~1,000 nucleotides per second with an error rate of about 1 in 10⁹ bases after proofreading.
Study This Concept
Practice DNA replication with free review games in these units: