Define Cell Cycle

In layman’s terms, the cell cycle can be defined as a series of events that take place intravenously in a cell leading to the formation of two daughter cells through DNA duplication and cytokinesis along with the division of cell organelles. These events take place for the purpose of the development and growth of the cell.

The Cell Cycle and Its Phases

The cell cycle, also known as the cell division cycle, is a 4-stage process that takes place in a somatic cell during which two significant molecular processes take place. These processes are the duplication of the parent chromosome, which takes place during the S phase of the cell cycle, and the equal distribution of the chromosomes to the daughter cells (occurring during M phase)

The phases of the cell cycle that occur in eukaryotic cells can be broken down into two important phases: interphase and the mitotic phase. During the phase known as interphase, the cell undergoes significant growth and replicates a DNA copy. During the mitotic phase, also known as the M phase, the cell divides its DNA into two sets, leading to the formation of two daughter cells and the conclusion of the mitotic cycle.

G1 (Gap 1) Phase

• This is the first stage of the interphase, also known as G1 or the first gap phase, and it is characterised by diminutive changes brought on by the increased biochemical activity of the cell. It is the primary stage of the interphase
• In addition to a wide variety of metabolic activities that ultimately result in the beginning of DNA replication, this phase is distinguished by the transition of the chromosomes from their condensed state to their expanded state
• In this phase, the chromatin fibres have characteristics that distinguish them from earlier phases: they are less coiled and thinner, fully stretched, and ready for transcription. The process of transcription results in the generation of RNAs as well as a sequence of protein molecules, both of which are necessary for the beginning of the DNA replication process
• G1 is the longest of the four phases, lasting significantly longer than the other three. Its duration also varies from cell to cell
• This is an important stage in the process during which the cell grows and assembles the chromosomal DNA building blocks and the related proteins. In addition to this, it stores sufficient amounts of energy in order to carry out the process of chromosome replication
• During this phase, the process of DNA synthesis starts off at a separate checkpoint. After the conclusion of all of the biochemical processes that are taking place at this particular stage, the cell moves one step closer to dividing

The S Phase, or Synthesis

• During this period of the interphase, DNA synthesis and the production of histones are both active
• In this location, the replication of chromosomes is made possible by connected proteins as well as the replication of DNA. Although some of the synthesis of histone proteins takes place during the G1 phase, the vast majority of it takes place during this phase
• Because the process of DNA replication is discontinuous and only semi-conservative, it results in the formation of identical pairs of molecules of DNA.
• The sister chromatids continue to be firmly connected to the centromeric region even after the number of chromosomes has been increased. The number of chromosomes in a cell’s nucleus does not change
• The centrosomes of animal cells, which are located at the centre of each animal cell, are connected to the centrioles, which are aligned in a direction that is perpendicular to one another. The centrioles play a functional role in the organisation of the process of cell division
• During this phase, the centrosome will undergo duplication, which will result in the production of the mitotic spindle, which is the apparatus that coordinates the movement of chromosomes when mitosis is occurring

G2 (Gap 2) Phase

• The S phase comes after this one and replaces it. In this case, each chromosome is composed of two chromatids, which results in the cell having twice as much DNA
• In this part of the cell, the cell regains its energy and produces proteins that are necessary for the chromosomes to manipulate
• Replication occurs in only a small percentage of the cell’s organelles. The cytoskeleton is disassembled in order to free up resources for the mitotic process
• There is a possibility of seeing further cell proliferation. The finishing touches of the preparations for the mitotic phase have to be put in place before the cell can go on to the first phase of mitosis

M Phase, or Mitotic Phase

• The G2 phase will follow immediately after this phase. At this point, the cell will divide into two daughter cells, and the chromosomes will be equally distributed across the two daughter cells. Following the transition from the M phase into the G1 phase, the subsequent cell cycle will start to be repeated. On the other hand, there are cells that skip the G1 phase entirely. These are known as G0 cells in the cell cycle

The following tiers of the process are included in it:

• This stage is characterised by the disappearance of the nucleus, the formation of spindle fibres, and the condensation of DNA into sister chromatids
• During metaphase, the sister chromatids align themselves along the plane of the cell equator by attaching their respective centromeres to the spindle fibres
• The stage of cell division known as anaphase is characterised by the separation of sister chromatids at the centromere, which occurs as a result of the mitotic spindle pulling them in opposite directions
• During telophase, the chromosomes reach the opposite poles of the cell and begin to unravel into tiny strands of DNA. The spindle fibres are lost. Nuclear membrane resurfaces
• Cytokinesis is the process in which the cell membrane divides and animal cells separate. The cell plate that eventually becomes the new cell wall is formed by plant cells
• Cells that have completed their life cycle and entered the G0 phase are in an inactive state because during this phase they are not actively preparing to divide into new cells. There are often only a few of these cells that continue to exist at this stage forever

Conclusion 

The cell cycle is a 4-stage process in a somatic cell that involves two major molecular activities. The S phase of the cell cycle involves chromosomal duplication and equitable distribution to daughter cells (occurring during M phase)

Eukaryotic cell cycle phases are interphase and mitosis. The cell grows and replicates DNA during interphase. During the mitotic phase, or M phase, the cell divides its DNA, forming two daughter cells and ending the mitotic cycle.