What is Mitosis? What are the Stages and Features?

For single or multicellular organisms, division is the only way to reproduce. One of these types of division is mitosis. Mitosis takes place after various stages.

The cell, which is surrounded by a membrane that protects itself, except that it contains organelles, begins to grow from the first moment it is formed. With the development of the organelles and the nucleus in it over time, it is time to divide. So what is mitosis? Let’s take a closer look at the bride’s stages and features.

Let’s start with the basics, what is mitosis?

Mitosis refers to the process of cellular division in which a single cell divides, resulting in two identical cells. By synonym, it means that both cells have the same number of chromosomes and genetic content.

Originally the term mitosis denoted nuclear division, which was not accompanied only by cytokinesis (division of the cytoplasm) in some cells, such as certain fungi, and in the fertilized eggs of many insects. Now the term mitosis is used interchangeably with the term cell division. However, it is not always available as it is another form of cell division, meiosis, involving sex cells.

How does mitosis take place?

Mitosis takes place in somatic cells, especially in the nucleus. The cell goes through a series of mitotic events that result in the formation of two identical daughter cells. Although these mitotic stages are the same in every asexual cell, they are different in plants. Before all mitotic events in plants, a phase called the prophase takes place.

So what are the stages of mitosis, in order?

• Interface
• Prophase
• prometaphase
• metaphase
• anaphase
• telephase

Interface:

Before the cell begins to divide by mitosis, the DNA in the cell is copied in preparation for cell division and two identical sets of chromosomes are formed. Outside the nucleus are two centrosomes, each containing a pair of centrioles, these structures are critical to the cell division process. Interphase is divided into 3 phases in itself;

G1 phase is the stage before DNA is synthesized. S phase is the stage in which DNA synthesis takes place. It is the phase in which the new cell formed as a result of the previous division grows and continues its normal activities. In other words, ATP, RNA, protein, enzyme and organelle synthesis take place. S phase is the stage in which DNA synthesis and replication take place. When the cell reaches the maturity of division, the order to divide comes from the nucleus thanks to the signal molecules. The G2 phase is the phase where DNA synthesis ends, DNA replication is controlled, and prophase begins. Here, too, ATP, RNA, protein and organelle synthesis continue.

Prophase:

Prophase occurs immediately after the S and G2 stages. Chromosomes evolve into X-shaped structures that are easily visible under the microscope. Each chromosome consists of two sister chromatids containing the same genetic information. Then the chromosomes pair up so that both copies of each chromosome are together. At the end of prophase, the membrane around the nucleus in the cell dissolves, releasing the chromosomes. Here the nuclear membrane begins to break down.

Prometaphase:

In prometaphase, the membrane surrounding the nucleus is completely disintegrated. Microtubules extending from the centromere reach the chromosomes.

Metaphase:

Chromosomes are arranged neatly along the equator, which is the center of the cell. Microtubules pull the chromosomes with equal force. Thus, each new cell that will form will be able to receive chromosomes.

Anaphase:

Separation of sister chromatids now indicates the onset of anaphase. These sister chromatids become chromosomes of small nuclei. Sister chromatids are then separated by the mitotic spindle, which pulls one chromatid to one pole and the other to the opposite pole. At this stage, the cell verifies that the newly formed cells have each identical chromosome.

Telophase:

It begins with the attraction of sister chromosomes to the poles of the resulting cells. At this stage, the nuclear membrane forms around the chromosomes in the nucleus, as in the mother cell. Thus, the chromosomes are separated from the cytoplasm.

Also, during this phase, the chromosomes unravel again. Mitotic spindle fibers disappear. The nucleolus regenerates in each daughter cell. After all this, cytokinesis, known as the stage in which the cell cytoplasm divides, begins as the final stage. The cytokinesis phase can sometimes begin in the anaphase phase.

What are the main features of mitosis?

• It promotes the growth of the organism
• Provides cell repair
• Replaces the cell with a new one
• Controls the cell division cycle

It ensures the growth of the organism:

An adult human is made up of billions of cells, and all cells in the body have the same genetic component. This genetic stability is achieved by mitosis. These cells in the body are formed by mitosis from the first cell zygote. The zygote divides by mitosis to form genetically identical daughter cells.

Provides cell repair:

External blows, wounds kill or damage cells. These damaged or dying cells should be replaced by cells of the same type with the same genetic quality. This is achieved by mitosis.

Replaces the cell with a new one:

Let’s take blood cells as an example. Red blood cells have a lifespan of 120 days. After 120 days, it should be replaced with new cells. This cell change is provided by mitosis. Similarly, skin cells are constantly replaced.

It performs the control of the cell division cycle:

The cell cycle is controlled by genes. Special signal molecules ensure that the cycle continues smoothly at 3 checkpoints, G1, G2 and M. The cell cycle is regulated by the stop and continue signals at these points. If the cell has reached a sufficient size at the G1 checkpoint, a continuation signal is given.

DNA damage and cell size are checked at the G2 checkpoint. If there is no problem, a continue signal is given. At the M control point, the attachment of the kinetochores to the spindle fibers is checked. If there is no problem, a continue signal is given. Disruption of cell cycle control for any reason causes cancer formation. These cells do not respond to the division signals, they divide continuously and cause tumor formation and thus the emergence of cancer disease.

Let’s take a closer look at the importance of mitosis:

The balance between the nucleus and the cytoplasm is achieved by mitosis so that the shape and size of the cell do not change. In multicellular organisms, a unicellular zygote develops into a multicellular embryo. By repeating the same process, the embryo eventually forms the multicellular organism. It is responsible for the transformation of the zygote into an adult. It forms reproductive organs in multicellular organism. Reproduction in eukaryotic organism takes place by this process. (as in Chlamidomonas).

Mitosis ensures the quantitative and qualitative distribution of chromosomes in all cells of an organism. It maintains a fixed number of chromosomes in all body cells of an organism. Any wound or broken part of organisms can be quickly repaired by mitosis. Diseases such as tumors and cancer are caused by uncontrolled mitosis.

Mitosis is used to produce genetically similar offspring. For example, budding of hydra and yeast, binary fission in amoeba, etc. Mitosis allows the sexually reproducing organism to grow and develop from a single cell to a sexually mature individual. This allows organisms to continue to reproduce for generations. It helps maintain a balance between the DNA and RNA content of the cell.