What is Mitosis and its phases ?

What is Mitosis?

Mitosis is a process of cell division in which a parent cell divides into two daughter cell with the same number of chromosomes.

So this is the complete definition of mitosis now lets understand it.

How a human develop from a single cell?

A human grows from only a single cell which happens due to the process of mitosis. Ovum fertilized with the sperm and then we call this single cell Embryo. Now the journey of complete human being formation starts from this single cell through the process of mitosis. Single cell(parent cell) continues to divide and form two cells(Daughter cells) and this process proceeds. 

Every human cell have 46 chromosome numbers, So when a cell divide into two new cells than these new cells also have 46 chromosome numbers. In mitosis Chromosome number is conserved and remain same as in the parent cell. That's why mitosis produce the identical cells. 

Phases of Mitosis

Mitosis has the four major phases which are:

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

In these phases karyokinesis occurs in which nucleus divides and after that cytokinesis in which cytoplasm divides.

What is interphase?

Interphase some times also called resting phase is a period before mitosis in which cell prepares itself for the division and it is a great biochemical activity.

Interphase has 3 stages:

1: G1(gap 1) is a period of extensive metabolic activity in which following activities are done:

• Cell grows in size
• Specific enzymes are synthesized
• DNA base unit are accumulated for the DNA synthesis

Some cells can exit the cell cycle and enter a phase which is called G0 If cell enters in this stage then no division occurs in the cells. We call it G not phase. Some body cells such as nerve cell and cells of the eye lense enters in the G0 phase and remain in this phase lifetime thats why our eyesight when once goes weak then it is difficult to restore the eyesight.

2: S-phase(Synthesis phase)

In this phase : Replication of the DNA occurs.

3: G2(Gap 2)

It is also called pre-mitotic phase because after it the cell enter in the mitosis. In this period energy is prepared for the chromosome movement, different protein are prepared, microtubules subunits are synthesized.

                                 

1: prophase

After the interphase cell enter in the mitosis first phase which is called prophase.

During prophase a fine thread like structure is seen inside the nucleus which is called chromatin. In the beginning of the prophase, chromatin material starts to condense and the we can see the chromosome in the cell with the light microscope during the prophase

• Chromosome becomes more and more thick and then their sister chromatids can be seen. The other changes that are seen during the prophase are:
• Nuclear envelope degenerates and disappear
• Nucleoli disappears
• Nuclear material is released in the cytoplasm
• Mitotic apparatus is arranged
• Cytoplasm becomes more viscous

 2: Metaphase(alignment of chromosomes)

Each chromosomes have two arms which are called the sister chromatids and these arms are attached at a point which is called centromere.

Centromere has a special area in the center which is made of protein and it is called kinetochore protein. On this protein mitotic apparatus is attached and then sister chromatids are separated.

Chromosomes align themselves at the equator of the cell in this phase. Mitotic apparatus arrange themselves on the poles of the cell.

                              

3: Anaphase(Seperation of the sister chromatids)

Most important and crital phase is anaphase. This is the phase in which chromosome"s chromatids are separated but with the same number of chromosomes in the daughter cells.

The kinetochore fibers attach at the kinetochore protein of the chromosome and then move towards their respective poles. At the same time polar microtubules elongates and due to their elongation the sister chromatids separates from the centromere point and move towarrds their respective poles.

4: Telophase

Telophase is actually the opposite of the prophase in which:

1. Chromosomes decondense and disappear as chromatin
2. mitotic apparatus diorganize
3. Nucleoli and nuclear membrane reorganize

But in this time the two nucleoli and nuclear membranes appear at their ooposite poles of the cell and after that cytokinesis occurs.