Mitosis its Phases and functions of mitosis

Mitosis

In biology, mitosis is the type of cell division in which two daughter cells are produced from a parent cell. In the mitotic type of cell division genetically identical type of cells are produced in which the amount of chromosomes is retained. Normally the mitosis is preceded by the S phase of interphase in which the DNA is replicated and then followed by the cytokinesis in which the cytoplasm divides.

Mitosis and cytokinesis define the mitotic division of the cell cycle. The process of mitosis is split into various stages or phases. These phases are

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

During the process of mitosis, the chromosomes that have already duplicated in the S level of interphase condense and attached to the spindle fibers that draw one copy of every chromosome to the opposing side of the cell that results in two genetically identical daughter nuclei. The cells then divide by the process of cytokinesis to produce two daughter cells.

Producing three or more daughter cells rather than two is a mitotic error called tripolar or multipolar mitosis. Other errors that occur during the process of mitosis can cause apoptosis or cause mutations. The mutation may give rise to certain types of cancer. Mitosis occurs only in the eukaryotic cells while the prokaryotic cells divide through a different process called binary fission.

Discovery of mitosis

In animal cells, the mitosis was first learned in the frog, rabbits, and cat cornea cells in 1873.  The word mitosis was coined by Walter Flemming in 1882 and it is a Greek word. The word mitosis is also used in a wide sense by some authors to make reference to karyokinesis and cytokinesis.

Phases of mitosis

The primary goal of the mitosis is to transfer the genetic material from the parent cells into the daughter cells. The genetic material consists of chromosome s that contain DNA in which hereditary information essential for proper cell function is present. Before the start of mitosis, the parent cell duplicates its chromosomes. The process of duplication occurs through the S phase of the interphase.

The chromosomes duplication results in two sister chromatids bound at the centromere. With the being of the process of mitosis, the chromosomes condense and become visible. The nucleolus that is present inside the nucleus and makes ribosomes disappears. Microtubules attached to the centromere and align the chromosomes.

After the anaphase phase in mitosis, the cell may experience cytokinesis. In which the cell membrane pinches inward between the two nuclei to create two new cells.

Cytokinesis will not always happen for example coenocytic cells experience mitosis without the process of cytokinesis.

Phases

Interphase
The mitotic phase is a short period that alternates with longer interphase in which the cell prepares itself for the division. Interphase is divided into G, S, and G2 stages. During these stages, the cell develops proteins and chromosomes are replicated.

The stages follow one another and are strictly regulated. The cell may temporarily or permanently leave the cell cycle and enter the Go period to avoid dividing. Some of the cells are capable of re-entering to the cell cycle.

Prophase
In this phase, the chromosomes condense and mitotic spindle formation starts. In this phase, the nucleus contains loosely packed chromatin. On the start of prophase become visible and can be seen at high magnification via a light microscope. At this stage, chromosomes are long and thread-like structures. Each chromosome has two sister chromatids that are joined at the site called centromere. In prophase, the nucleolus disappears and gene transcription ceases.

Prometaphase
In this phase, the nuclear envelope disintegrates due to which the microtubules invade the nuclear space. That is called open mitosis and occurs only in some multicellular organisms. A number of microtubules connect to the microtubule of the opposite side and create the mitotic spindle. The microtubules attached to the kinetochore which uses energy from the ATP and supplies the filling force that is essential to later separate the chromatids.

Metaphase
After the microtubules located on the kinetochores, the two centrosomes begin the pulling of chromosomes toward the opposite end of the cell. To make equal distribution the metaphase ensures that the chromosomes are aligned over the equatorial plate. After this event, the cycle proceeds to the anaphase.

Anaphase
In this phase, the sister chromatids are cleaved and identical daughter chromosomes are produced. The kinetochores microtubules pull the daughter chromosomes to the other end of the cell. In this phase, the cell elongate and the condensation of the chromosomes reaches the maximum that helps in the chromosome separation and the reformation of the nucleus.

Telophase
In this phase, the microtubules lengthen and the cell elongate even more. A fresh nuclear envelope is formed around each group of separated daughter chromosomes. The nucleolus reappears.  The chromosomes start decondensation and now mitosis is complete.

Cytokinesis
It is not a stage of mitosis but is required to complete cell division. In this stage, a cleavage furrow appears pinching from the separated nuclei. The cleavage furrow grows and lastly divide the cell into two daughter cells. The end of cytokinesis marks the finish of the M phase.  There are many types of cells in which the cytokinesis and mitosis occur separately due to which single cells with multiple nuclei are formed.

Functions

1. Development and growth. The number of cells increases by mitosis and this is the basis of the development of a multicellular body from a single cell. For example, the zygote.

2. Cell replacement. In some areas of the body such as epidermis, immune system, and digestive system the cells are constantly sloughed off and replaced by the new ones. these new cells are created through the process of mitosis. In the same way, the red blood cells have a short life span after which they die and to fulfill the needs new RBC’s are created by the process of mitosis. So mitosis creates new blood cells.

3. Regeneration. Some organisms can regenerate areas of the body. The development of cells in many cases is attained by mitosis. For example, starfish regenerate lost arms through the process of mitosis.