Ongoing replication refers to the process of DNA replication that is continuously happening in a cell during the specific phase of its cell cycle known as the S phase (for Synthesis). This is when the cell duplicates its DNA, creating two identical copies of each chromosome to ensure that each daughter cell will receive a complete set of chromosomes during cell division.
The process of DNA replication involves several key steps:
- Initiation: The process begins at specific points in the DNA called origins of replication. Proteins bind to the origins, unwinding the double helix and creating a replication bubble.
- Elongation: New DNA strands are synthesized by the enzyme DNA polymerase. This process occurs in both directions along the DNA strand, creating a replication “fork” at each end of the replication bubble.
- Termination: Replication continues until the entire molecule of DNA has been copied.
It’s important to note that DNA replication is highly regulated to ensure accuracy. Errors in DNA replication can lead to mutations, which can potentially cause diseases like cancer. Cells have several mechanisms to correct errors that occur during DNA replication, such as DNA repair pathways and cell cycle checkpoints that can halt the cell cycle to allow time for repair.
When DNA damage is too severe and cannot be repaired, or when cells have reached their replicative senescence (as I described in the previous response), the cell may undergo programmed cell death (apoptosis) to prevent the propagation of damaged DNA to daughter cells.
In the context of cancer, ongoing replication in the presence of DNA damage, genomic instability, or non-functional p53 can lead to the accumulation of mutations and promote tumor progression.
