Cell Cycle, Mechanism, and its various Phases For Class 11th and NEET


We are well known that the Cell, The Basic Unit of Life, makes up all living beings. The zygote created as a result of fertilization divides indefinitely, resulting in a multicellular creature. The multi-faceted, cellular complexity and body organization of a cellular organism are astounding. The proliferation of cells From a single parent cell, two daughter cells are produced. There are two primary steps involved:

(1) Cell Growth

 (2) Cell Division

Cell Cycle: Definition

The Cell Cycle is a well-ordered sequence of events that results in cell division and the formation of two daughter cells that are identical to their parents. It is a highly controlled mechanism that is required for appropriate cell function (growth). Any interruption in the regulation of the cell cycle has the potential to cause cancer. Despite the scientific community’s intense interest in finding a solution for this threat, one-sixth of the world’s population is being hunted by it. Cell division happens in all living species, but it occurs in prokaryotes and eukaryotes in diverse ways. Prokaryotic cells have a basic shape, no nuclear membrane, and a single circular chromosome in their genome. As a result, binary fission is used to divide it.

Aspects of the Cell Cycle in History

Cell cycle phases were discovered in 1970, and a general mechanism for regulating the commencement of cell cycle phases was discovered. The Go phase has been recognized.

Mechanism of cell cycle control – Pardee (1974) concentrated on the cell cycle’s regulatory mechanism. He figured out how cells switch from the proliferative to the Go phases of the cell cycle. Scientists discovered how centromeres assisted in chromosomal segregation and extracted a functional centromere from budding yeast in 1980. During the cell cycle, they detected cyclic fluctuations in the amounts of cyclins.

Origins of replication sites were discovered in 1980, which led to the discovery of cell cycle checkpoints and associated control mechanisms. The cell cycle checkpoints were found and their control mechanisms were elucidated, and the entire mechanism—how damaged DNA arrests the cell cycle via checkpoint regulation and P53—was discovered. Cyclin-dependent kinase (a novel protein class) is discovered in 1990. Cyclin C, D, and E were discovered in new classes, and CDK inhibitors were discovered. The chemicals CDK and cyclin, which control the cell cycle in eukaryotic cells, were discovered. In biology and medicine, it was a fantastic breakthrough. Scientists are currently concentrating on particular treatments for various stages of the cell cycle as well as diseases associated with it.

Cell Cycle Explanation

When cell division is examined under a microscope, a succession of changes occurs within 1 second, ranging from chromosome condensation through chromosome alignment and segregation. In human cells for one hour Such drastic alterations, on the other hand, are not typical. The following step will take more than 20 hours. A dynamic shift to take place. During this time between cell divisions, what do cells do? The process through which the structural components of cells proliferate is known as multiplication. The cell’s components, such as chromosomes, are doubled. The process of segregation into two cells is repeated. This procedure is known as the cell cycle

In a typical eukaryotic cell, the cell cycle contains two main phases:

Interphase – The time between the end of the first cell division and the start of the second cell division, during which the cell is primarily involved in cell growth and a variety of metabolic activities.

The M Phase (Mitosis Phase) is the actual division phase of the cell.

The interphase is split into three parts:

During the G1 phase, cells synthesize RNAs and proteins and prepare for DNA and chromosomal replication. The cell is metabolically active and continues to develop throughout the G1 phase, but it does not duplicate its DNA.

The S phase (Synthesis) is the time when DNA is synthesized. Although the number of chromosomes remains constant, the amount of DNA per cell doubles. Proteins for mitosis are generated in the G2 phase of the cell cycle. Cells continue to multiply.

The dividing phase is included in the M – Phase. It comprises of the following elements: Prophase, Metaphase, Anaphase, Telophase

It’s worth noting that a human cell growing in a cell culture medium completes its cell cycle in roughly 24 hours, and cell division takes around an hour. Over 95% of the cell cycle is spent in the interphase.

1. One of the most important events of the G1 phase is cell proliferation. In the cell cycle, the G1 phase is the most varied in terms of time.

2. In the cell cycle, the shift from G1 to S is a crucial regulatory point.

3.G2  (the gap between S and M). This gap phase is used to guarantee that the genetic material (DNA) is properly copied and packed by proofreading it.

4. When cells cease dividing and depart the cell cycle due to a lack of growth-promoting signals they are said to be in G0 or quiescence (Quiscent phase). They can live for days, weeks, or even a lifetime in some cells (e.g. nerve cells, eye lens cells).

The cell cycle is “excited” by the majority of differentiated cells. Both positive and negative regulatory signaling molecules play a role in the orderly progression through each phase.

A eukaryotic chromosome has three important components:

Centromere, The chromosome’s attachment point for spindle microtubules. Before cell division, the kinetochore (a protein structure) assembles on the chromosome.

Telomeres are the natural tips (ends) of chromosomes that give stability. The site where DNA synthesis begins is known as the origin of replication.

During metaphase, the kinetochore (a multiprotein complex) forms at each centromere. Sister chromatids’ kinetochores then link up with microtubules from opposite spindle poles. Sister chromatids separate and travel to opposing poles during anaphase, resulting in two daughter cells.

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