DNA replicates through a precise biological process that ensures each new cell receives an exact copy of the genetic material. This process occurs during cell division and involves several key steps:
Steps of DNA Replication
1. Initiation (Preparing for replication)
- DNA replication begins at specific locations on the DNA called origins of replication.
- An enzyme called helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds between base pairs, creating a Y-shaped structure called the replication fork.
- This separation exposes each strand to serve as a template for new DNA synthesis
2. Elongation (DNA synthesis)
- DNA strands are antiparallel, so replication occurs differently on each strand:
- The leading strand is synthesized continuously in the 5' to 3' direction toward the replication fork.
- The lagging strand is synthesized discontinuously in short fragments called Okazaki fragments away from the replication fork.
- DNA polymerase enzymes add complementary nucleotides (A pairs with T, and C pairs with G) to the exposed template strands.
- Primase synthesizes short RNA primers to provide starting points for DNA polymerase.
- On the lagging strand, multiple primers are used, and DNA polymerase synthesizes Okazaki fragments that are later joined together
3. Termination (Finishing the process)
- RNA primers are removed by exonuclease enzymes.
- DNA polymerase fills in the gaps with DNA nucleotides.
- DNA ligase seals the fragments into continuous strands.
- The two resulting DNA molecules each contain one original (parental) strand and one newly synthesized strand, making replication semi-conservative.
- The DNA rewinds into its double helix structure
Additional Details
- DNA replication occurs during the S phase of the cell cycle.
- Multiple proteins and enzymes coordinate the process, ensuring high fidelity with proofreading mechanisms to minimize errors.
- In eukaryotes, replication starts at multiple origins to complete the process efficiently, while prokaryotes typically have a single origin
This coordinated mechanism ensures that genetic information is accurately copied and passed on to daughter cells during growth, repair, and reproduction.
