Summary
Highlights
DNA replication is the process where DNA copies itself. This is crucial before a cell divides during mitosis, ensuring that both resulting daughter cells receive an identical copy of the original DNA. DNA replication occurs during the S phase of the cell cycle, with 'S' standing for synthesis.
Inside the nucleus, DNA exists as a double helix, with two strands connected by hydrogen bonds between nitrogenous bases. The first step in replication involves the enzyme DNA helicase, which unwinds and separates these two strands by breaking the hydrogen bonds. Each separated half then serves as a template for a new DNA strand, exposing the nitrogenous bases to free nucleotides.
The second step involves the creation of two new, identical DNA strands, assisted by the enzyme DNA polymerase. This enzyme adds free nucleotides from the nucleus to the original template strands. DNA polymerase creates new hydrogen bonds according to the base-pair rule: adenine bonds with thymine, and guanine bonds with cytosine. This results in each template strand forming a complementary mirror image.
After replication, two duplicate DNA molecules are produced from the original. This prepares the cell for mitosis. In summary, DNA replication duplicates DNA during the S phase, ensuring identical DNA for daughter cells. DNA helicase unwinds the DNA, and DNA polymerase adds nucleotides based on the base-pair rule, resulting in two identical DNA molecules.