DNA Replication in S Phase

DNA replication, which takes place in the S phase of the cell cycle, increases the amount of DNA present in cells. Each new cell receives an accurate duplicate of the genetic data present in the original cell thanks to the highly coordinated and precise process of DNA replication. There are numerous crucial steps in this process, which takes place in the nucleus of eukaryotic cells:

1. Initiation: At locations on the DNA molecule known as the origins of replication, the process of DNA replication starts. These locations are recognized by enzymes and proteins, which then start the double-stranded DNA helix unwinding process.

2. Unwinding and Separation: Helicase enzymes separate the double helix, resulting in the formation of two single-stranded DNA templates. As a result, DNA synthesis takes place inside a replication bubble that has two replication  forks, where DNA synthesis will occur in both directions.

3. Priming: Short RNA primers that are complementary to the single-stranded DNA templates are created by the primase enzyme. These primers serve as the scaffolding for the synthesis of DNA.

4. DNA Synthesis (Elongation): As the DNA strands grow, complementary nucleotides are added by DNA polymerase enzymes after they have bound to the primers. The direction of DNA synthesis is 5' to 3', indicating that the 3' end of the developing strand receives additional nucleotides. The DNA molecule is antiparallel, which causes the two DNA strands to replicate in different orientations.

5. Okazaki Fragments (Lagging Strand): Since DNA synthesis only happens in one direction on each template strand, the strand facing the opposite direction only undergoes intermittent synthesis. This results in the formation of short DNA fragments called Okazaki fragments on the lagging strand.

6. Ligation and Repair: DNA polymerases continue to add nucleotides until they reach the template's end or come across an Okazaki fragment that has already been created. DNA ligases are enzymes that fill in the gaps between adjacent fragments to form a continuous DNA strand.

7. Termination : DNA replication keeps going in both directions until the whole DNA molecule has been copied. All DNA areas are replicated when the replication forks from adjacent bubbles come together and merge, which marks the end of replication.

By the end of the S phase, the DNA replication process had produced two identical DNA molecules, each made up of a freshly synthesized ("daughter") strand in addition to the original ("parental") strand. During the future phases of the cell cycle, these two DNA molecules will be divided into two daughter cells.

Overall, DNA replication during the S phase makes certain that each cell receives an exact and complete copy of the genetic data required for proper cellular function and inheritance.