Explanation of Cell Cycle, Division, and Phases

Introduction

Cell division may be known as the process by which a parent cell separates into two or more daughter cells. It generally occurs as part of a larger cell cycle. There are two different types of eukaryotic cell division. Nutritional division, in which each daughter cell is genetically identical to the mother cell (thread division), and germ cell division, in which the number of chromosomes in the daughter cell is made 1/2 to produce haploid gametes (meiosis). 

Cell Cycle

The cell cycle or cell-division cycle is a series of events that occur within a cell and divide into two daughter cells. These events include the replication of its DNA (DNA replication) and some organelles, as well as the division of the cytoplasm and other components into two daughter cells in a process called cell division. 

Cell cycle in cells with nuclei

In cells with nuclei (eukaryotes, i.e. animals, plants, fungi, and protist cells), the cell cycle is the two major phases of interphase and mitosis (M)  (including mitosis and cytokinesis). It can be divided into stages. During interphase, cells grow, collect the nutrients needed for mitosis, and replicate their DNA and some organelles. 

Cell cycle in cells without nuclei

In anucleated cells  (prokaryotes, i.e. bacteria and archaea), the cell cycle is divided into periods B, C, and D. Period B lasts from the end of cell division to the beginning of DNA replication. DNA replication occurs during the C period. Period D indicates the stage from the end of DNA replication to the division of bacterial cells into two daughter cells. 

Phases of the Cell Cycle

The eukaryotic cell cycle includes 4 wonderful phases: G1 section, S section (synthesis), G2 section (together called interphase), and M section (mitosis and cytokinesis). M section is itself composed of tightly coupled processes: mitosis, wherein the cell`s nucleus divides, and cytokinesis. Cells that have temporarily or reversibly stopped dividing are said to have entered a quiescent state called the G0 phase. 

G0 phase (quiescence):

G0 is the resetting phase when cells leave the cycle and stop dividing. The cell cycle begins at this stage. Non-proliferative (non-dividing) cells of multicellular eukaryotes generally enter the G1 to G0 resting state and can remain dormant for long periods, and in some cases indefinitely (as is often the case with neurons). 

Interphase:

Interphase shows the section between two consecutive M phases. Interphase is a series of changes that occur in newly formed cells and their nuclei before they can divide again. Interphase usually lasts at least 91% of the total time required for the cell cycle. 

Interphase progresses in three stages, G1, S, and G2, followed by a cycle of mitosis and cytokinesis. The nuclear DNA content of cells is replicated in the S phase. 

G1 phase (First growth phase):

The first phase within the interphase from the end of the previous M phase to the start of DNA synthesis is called G1 (G stands for gap). Also called the growing phase. In G1, the cell has three options: 

1. Continuation of the cell cycle and entry in the S phase.
2. It stops the cell cycle, enters the G0 phase, and differentiates. 
3. Since it stopped in the G1 phase, it can enter the G0 phase or return to the cell cycle. 

S phase (DNA replication):

The next S phase begins when DNA synthesis begins. When complete, all chromosomes will be replicated. That is, each chromosome is composed of two sister chromatids. At this stage, the amount of DNA in the cell doubles, but the ploidy and the number of chromosomes do not change. 

G2 phase (growth):

The G2 phase is a period of protein synthesis and rapid cell proliferation that occurs after DNA replication and prepares cells for mitosis. 

Mitotic phase (chromosome separation):

The relatively short M phase is composed of fission (nuclear movement). It is a usually short phase of the cell cycle. The pattern of events is divided into phases. Phases correspond to the completion of activity in one group and the start of the next. These phases, in turn, are  known as: 

1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase 

Cytokinesis phase (separation of all cell components):

Immediately after mitosis, cytokinesis occurs, dividing the nucleus, cytoplasm, organelles, and cell membranes into two cells that contain approximately equal proportions of these cellular components. Mitosis and cytokinesis together define the division of mother cells into two daughter cells that are genetically identical to each other and their parent cells. It occupies about 10% of the cell cycle. 

Conclusion

The cell cycle, whether eukaryotic or prokaryotic, is the replication and replication of cells. Although important to living things in many ways, they can survive as a whole. In the case of Prokaryotes, a cell cycle called demitration allows them to divide into two new daughter cells and stay alive.