Cell, also called as the building block of life, is the most basic functional unit of all living organisms. Cells are organisms onto themselves, like most bacteria or amoeba which are unicellular (having a single cell) or can be functional units that make up our body, such as human beings that are multicellular, comprising approximately 100 trillion of cells. Cell cycle or cell division cycle is basically a series of events which occurs during cell division and replication. In prokaryotic cells, i.e. cells without nucleus, the cell cycle occurs through a process called binary fission.
While in eukaryotic cells, i.e. cells with nucleus, the cell cycle can be divided into four distinct phases: G1 phase (cell growth period), S phase (DNA synthesis or replication occurs), G2 phase (cell undergoes a period of rapid growth to prepare for mitosis) and M phase (mitosis). G1 phase, S phase and G2 phase are collectively known as interphase, wherein the cell grows, collects nutrients for mitosis and duplicates its DNA, and M phase (mitosis and cytokinesis), is the process in which the cell divides itself into two distinct cells, termed as daughter cells. Hence, in this article we will try to learn the entire process of mitosis or the various cell division stages.
Mitosis-Process of Cell Division
Mitosis is the cell division process wherein the eukaryotic cell splits the chromosomes (thread like strands of DNA) in its cell nucleus in to two identical sets in two separated nuclei. The process is instantly followed by cytokinesis, in which the nuclei, cytoplasm, organelles and cell membrane get divided into two separate cells having equal proportions of these cellular components. Hence, mitosis and cytokinesis together form the mitotic (M) phase of the cell division cycle, wherein the mother cell gets divided into two daughter cells which are genetically similar to each other and their parent cell. These sequence of events are divided in to cell division stages: interphase, prophase, prometaphase, metaphase, anaphase and telophase.
Cell Division Stages for Kids
Interphase: This is the first stage of cell division wherein the cell is engaged in metabolic activity and prepares itself for cell division process. Interphase comprises of three phases, including G1, S and G2 in which the cell matures by producing proteins and cytoplasmic organelles. In this phase, the DNA replicates but has not yet formed a condensed clear structure of chromosome. Hence, chromosomes are not clearly discerned in the cell nucleus and can be seen as loosely coiled chromatin (DNA molecules). The cell contains a pair of centrioles (small cylindrical cell organelles), nucleolus (a dark, circular body of protein in cell nucleus) and a nuclear membrane to keep the DNA molecules from undergoing mutation.
Prophase: In this stage, the chromatin begins to shorten and condense due to coiling, to form chromosomes. Centrioles start moving to the opposite ends of the cell and the spindle fibers extend from the centromeres (condensed region of each chromosome). The nuclear membrane and nucleolus can no longer be seen now.
Prometaphase: In prometaphase, each chromosome forms two kinetochores (protein structure on chromosomes) at the centromere, one attached at each chromatid. Microtubules (structural components of the cell) attach at the kinetochores and the chromosomes start moving.
Metaphase: The spindle fibers attach themselves to the centromere of the chromosomes and align them along the middle of the cell nucleus. The line is referred as the equatorial plate or metaphase plate. This alignment will ensure that in the next phase, when the chromosomes will separate, each newly formed nucleus will get one copy of each chromosome.
Anaphase: In this phase, as the spindle fiber shorten and the centromere splits, the paired chromosomes will separate and start moving to the opposite sides of the cell. Though the reason for this motion is still unknown, according to some studies, it is the rapid assembly and breakdown of microtubules that may cause this movement. Hence, at the end of anaphase, we get two separate identical copies of sister chromosomes.
Telophase: In telophase, the sister chromosomes attach at the opposite ends of the pole and a new nuclear membrane is formed around each set of sister chromosomes. The spindle fibers also disintegrate.
Cytokinesis: Though not a phase of mitosis, cytokinesis is a separate process that completes the entire process of cell division. It is a process of splitting the daughter cells apart by forming a furrow wherein the cell is pinched in to two. By the end of this process, each daughter cell has a complete copy of the genome of its parent cell, i.e. same number and quality of chromosomes.
To sum up, we can say that mitosis or the cell division process is essential for maintaining and controlling the chromosomal set so that each daughter cell has chromosomes which are alike in composition and number to the chromosomes of the parent cell. I hope after reading this article you will have a fair idea of what is cell division and what are the different cell division stages.