CELL DIVISION-MITOSIS Have you ever thought: Whenever there is any cut or wound in any of our body part, how the get healed up? How do a small baby grows into an adult? How does the growth takes place in our body?
These questions might appear very simple to us but they aren't! The healing up of wounds, growth of an individual and all the repairs which takes place in our body is due to the cell division. Now the next question which comes to our mind is What is Cell division and actually how it occurs?
Cell division is the process by which a parent cell divides into two or more cells called daughter cells. Cell division usually occurs as part of a larger cell cycle. All cells reproduce by dividing into two, with each parental cell giving rise to two daughter cells every time they divide. There are two types of cell division: mitosis and meiosis. Most of the time when people refer to “cell division,” they mean mitosis, the process of making new body cells and it occurs in all somatic cells. Meiosis is the type of cell division that creates egg and sperm cells i.e. Germ cells which are helpful in sexual reproduction. It ensures that humans have the same number of chromosomes in each generation. It is a two-step process while Mitosis is single step. Meiosis also allows genetic variation through a process of DNA shuffling while the cells are dividing and mitosis lack that. In this article we will see the process of Mitosis in an elaborate way: Mitosis is a fundamental process for life. During mitosis, a cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells. Mitosis is a process where a single cell divides into two identical daughter cells. The characteristics of Mitosis are:
- During mitosis one cell divides once to form two identical cells.
- The major purpose of mitosis is for growth and to replace worn out cells.
- It occurs only in somatic cells.
- Chromosomal no. are not reduced in this type of division.
- It does not allow genetic recombination.
- If not corrected in time, mistakes made during mitosis can result in changes in the DNA that can potentially lead to genetic disorders.
Mitosis has the following 4 Phases i.e. The cell divsion occurs in the following 4 steps:
The first step of cell division is prophase, during which the nucleus dissolves and the chromosomes begin migration to the midline of the cell. The characteristics of this stage are: The chromosomes condense into X-shaped structures that can be easily seen under a microscope. Each chromosome is composed of two sister chromatids, containing identical genetic information. The chromosomes pair up so that both copies of all the chromosomes are together. At the end of prophase the membrane around the nucleus in the cell dissolves away releasing the chromosomes. The mitotic spindle, consisting of the microtubules and other proteins, extends across the cell between the centrioles as they move to opposite poles of the cell.
The second step, known as metaphase, occurs when all the chromosomes are aligned in pairs along the midline of the cell. The characteristics of this stage are: The chromosomes line up neatly end-to-end along the centre (equator) of the cell. The centrioles are now at opposite poles of the cell with the mitotic spindle fibres extending from them. The mitotic spindle fibres attach to each of the sister chromatids.
As the cell enters anaphase, the chromatids, which form the chromosomes, will separate and drift toward opposite poles of the cell. The characteristics of this stage are: The sister chromatids are then pulled apart by the mitotic spindle which pulls one chromatid to one pole and the other chromatid to the opposite pole.
As the separated chromatids, now termed chromosomes, reach the poles, the cell will enter telophase and nuclei will start to reform. The characteristics of this stage are: At each pole of the cell a full set of chromosomes gather together. A membrane forms around each set of chromosomes to create two new nuclei. The single cell then pinches in the middle to form two separate daughter cells each containing a full set of chromosomes within a nucleus. This process is known as cytokinesis.
End of mitosis is marked by Cytokinesis, Iin which nuclei have reformed and the cell membrane begins to separate the cell into two daughter cells,The mitotic phase which includes both mitosis and cytokinesis is the shortest part of the cell cycle. The whole procedure is very similar among most eukaryotes, with only minor variations. As prokaryotes lack a nucleus and only have a single chromosome with no centromere, they cannot be properly said to undergo mitosis.