Mitosis and its stages

Mitosis

Cells can divide, and in unicellular organisms, this makes more organisms. In multicellular organisms, cell division is used for growth, development, and repair of the organism. Cell division is controlled by DNA, but exact copies of the DNA must be given to the daughter cells . Bacteria reproduce by a simple process called Binary fission. They have one chromosome which is attached to the cell membrane. This chromosome replicates, then the two copies are pulled apart as the cell grows. Eventually the cell pinches in two to make two cells. Eukaryotes do mitosis. In mitosis, each daughter cell gets about half of the cytoplasm from the mother cell and one set or copy of the DNA.

Before cell division occurs, the cell first has to replicate the chromosomes so each daughter cell can have a set of chromosomes. When the chromosomes are replicated and getting ready to divide, they consist of two, identical halves called sister chromatids which are joined by a central region, the centromere. Each chromosome is one long molecule of DNA and special proteins "the histone protein". DNA makes up the genes, and that genes are linearly arranged on chromosomes . Some of the proteins in the chromosomes “turn off” the genes that are not needed in that cell. For example, while every cell in your body contains exactly the same genes, you don’t need your eye-color gene operational in cells in your big toe, nor toenail-shape genes active in cells in your stomach.

Two basic types of cells

Two basic types of cells  occur in the bodies of Eukaryotes.

Somatic cells: are general body cells which have the same number of chromosomes as each other within the body of an organism. The number of chromosomes in somatic cells is consistent among organisms of the same species, but varies from species to species. These chromosomes come in pairs, where one chromosome in each pair is from the mother and one is from the father.

Since most organisms have more than one pair of chromosomes, it would also be correct to say that the organism received one set of chromosomes from its mother and one matching set from its father, and that these sets match in pairs.  

Reproductive cells        

The other type of cells found in eukaryotes are the Reproductive cells, gametes or sex cells, consisting of eggs in females and sperm in males. 

These special reproductive cells have only one set of chromosomes consisting of one chromosome from each pair.

 In humans, the somatic cells have 46 chromosomes arranged in 23 pairs, while gametes have 23 individual chromosomes. 

In fruit flies, somatic cells have 8 chromosomes  2 sets and gametes have 4 chromosomes  1 set. The term “ploid ”is used  to refer one set of chromosomes in an organism, and that term is typically combined with another word stem that describes the number of sets of chromosomes present. For example, a cell with one set of chromosomes is called haploid, a cell with two sets of chromosomes is diploid, and a cell with four sets of chromosomes is tetra ploid.
Mitosis is the process of division of the chromosomes, while cytokinesis is the process of division of the cytoplasm to form two cells. In most cells, cytokinesis follows or occurs along with the last part of mitosis.
Centrioles consist of nine sets of three microtubules, occur in animal cells only, and are involved in division of the chromosomes. Each animal cell has a pair of centrioles located just outside the nucleus. The two centrioles in the pair are oriented at right angles to each other. Just before mitosis, the centrioles replicate.

Stages in mitosis include 

interphase, prophase, metaphase, anaphase, and telophase. Remembering “IPMAT” or Intelligent People Meet At Three 

1. Strictly speaking, interphase is the stage in which a cell spends most of its life and is not part of the process of mitosis, per se, but is usually discussed along with the other stages.Interphase may appears to be a “resting” stage, but cell growth, replication of the chromosomes, and many other activities are taking place during this time. Near the end of interphase just before the cell starts into the other stages of mitosis, if the cell is an animal cell, the centrioles replicate so there are two pairs. At this time, the strands of DNA that make up the chromsosomes are unwound within the nucleus and do not appear as distinct chromosomes. Thus, at this stage, the genetic material is often referred to as chromatin 
2. In prophase, the chromosomes start to coil, shorten, and become distinct. In animals, the centrioles begin to migrate to the poles of the cell. The mitotic spindle or polar fibers begin to form from the poles of the cell towards the equator. In animals, this starts as asters around the centrioles.As the spindle mechanism finishes growing toward the equator and interacts with the centromeres to line up and, later, move the chromosomes. Also at this time, the nuclear envelope starts to disintegrate. 
3. Metaphase is characterized by the lining up of the chromosomes along the equator of the cell or what is called the metaphase plate. The nuclear envelope has totally disintegrated and the polar fibers have reached the centromeres of the chromosomes and have begun interacting with them. 
4. In anaphase, the sister chromatids separate at the centromeres, thus can now be called chromosomes. These are pulled to the poles of the cell by the mitotic spindle.
5. In telophase, the new daughter nuclei and nuclear envelopes start to reform and the chromosomes uncoil. Telophase frequently includes the start of cytokinesis. In animal cells, cytokinesis starts with a cleavage furrow or indentation around the middle that eventually pinches in, dividing the cell in two. In plants, cytokinesis begins with a series of vesicles that form at the equator of the cell, which subsequently join until the cell is divided in two.