The S Phase of Cell Division

Cell division entails the division of a parent cell into multiple progeny cells. Cell division is a very important process for the maintenance of life. The two types of cell divisions; mitosis and meiosis, vary in the process that is followed for the division of cells and also the number of daughter cells that are formed after the process of cellular division. 

The process of cell division consists of a preparatory phase and an actual phase where cell division takes place. The preparatory phase is also known as the interphase. Interphase can be further divided into three different phases based on the preparatory activities that take place during that particular phase.

Interphase

Interphase is the part of the cell cycle that involves the various activities of the cell that are required for the preparation of the process of cell division. This phase does not show any microscopic changes because the cell morphology does not go through many changes. 

Interphase consists of three different phases: the G1 phase, the S phase and the G2 phase. The G1 phase is characterised by the growth of the cells, the S phase is characterised by the synthesis of genetic material and the G2 phase is characterised by the preparation of the cell for the actual cell division. 

During the process of cell division, the interphase is the part where the cell spends the longest time in. The stage of actual cell division is much shorter. 

Stages of interphase 

During the G1 phase, the cell grows and functions as a normal cell. This process is also accompanied by a high amount of protein synthesis. This means that the cell grows in size and the cellular organelles that are present inside the cell also grow in number. During this phase the number of cytoplasm increases. 

The next stage is called the S phase. During this phase, the amount of genetic material is doubled. Despite the increase in the amount of genetic material, the number of chromosomes remains constant. 

The next phase is called the G2 phase. During this phase, the cell continues to prepare for the process of division. This phase is also characterised by the division of cell organelles such as mitochondria and chloroplast. 

Synthesis phase

The S phase, which is also known as the synthesis phase, is the phase of the cell cycle that consists of the replication of the genetic material present inside the cell. This phase occurs between the G1 and the G2 phases. 

The process of cellular replication is very critical for the success of the process of cell division. Due to this, several checks have been placed through the entirety of the synthesis phase. 

i) Regulation of S phase 

When the cell enters the S phase, its entry is regulated by a checkpoint called the G1 restriction point. This checkpoint is used to ensure whether the cell possesses an adequate amount of nutrients that are required for it to continue the process of cellular division. 

This process is irreversible and once the cell passes this checkpoint it will go forward to complete the entire S phase. 

Several enzymes carry out these checks and their composition varies from organism to organism. Some of these enzymes perform actions such as regulation of transcription and expression of certain genes. 

ii) DNA replication during the S phase

During the S phase, the process of replication of the genetic material takes place. This process is very important because replication of DNA is required so that the genetic material can be equally distributed among the daughter cells. 

For the process of DNA replication, the formation of a replication fork is required. A replication fork is formed by the unwinding of the two strands of DNA. 

Once the DNA strands are unwound, the enzymes that are required for the process of DNA replication bring in nucleotides that are complementary to the existing DNA strand and it leads to the formation of two new strands of DNA. 

iii) Importance of S phase

The S phase is a very important part of the cell cycle. This phase involves the duplication of the genetic material of the cell. This is of great importance because it helps in encoding the genome before the cell divides. 

The transition from the G1 phase to the S phase is also particularly important because it leads to the production of certain enzymes that are required to carry out various checks and to proceed with the cell cycle smoothly. 

Conclusion

It can be concluded that the S phase is an important part of the cell cycle. The cell cycle is divided into the interphase and the division phase. The interphase is the preparatory phase wherein the cell prepares for the process of division. 

The interphase is further divided into the G1, S and G2 phases. The S phase involves the division of genetic material inside the cell. This process is important because the genetic material needs to be duplicated before it can get equally divided among the two daughter cells. 

The S phase also includes various checkpoints because it is very important to check if the replication process of DNA has taken place correctly. Failure to do so can lead to faulty cell division and can also cause chromosomal abnormalities in the organism.