In this section, you will learn and understand the 4 stages of mitosis. Mitosis is a special type of cell division, in which a parent cell divides into four diploid (2n) cells. This cell division comprises two further divisions i.e. karyokinesis (a division of the nucleus) and cytokinesis (a division of the cytoplasm). The karyokinesis of mitosis further consists of 4 stages, prophase, pro metaphase, metaphase, anaphase, and telophase. The 4 stages of mitosis are demonstrated in the section by the diagram. Now let’s discuss the 4 stages of mitosis.
4 stages of Mitosis
Introduction to Mitosis
The term Mitosis was first described by Walther Flemming in the 1880s. Mitosis is derived from the Greek word for thread, reflecting the shape of mitotic chromosomes.
Basically, mitosis consists of two phases (1) Interphase and (2)Mitotic phase. Inter phase is the larger phase. It further consists of three phases namely (a) the G1 phase which is known as the gap first phase (b) the S phase which means synthesis because DNA is replicated in it and(c) the G2 phase which is called the second gap phase.
In the G1 phase of interphase cell produces enzymes and organelles. The cell also regained its size in it. In the S phase replication of DNA is completed as result, each chromatid is converted to two sister chromatids. The G2 phase is also called pre mitotic phase because the cell has prepared for division in this phase. Microtubules that produce spindle fibers develop in the G2 phase.
During the Interphase G0 phase sometimes is present. Generally, a cell goes from G1 to the S phase and then G2 but in some cells, a cell directly goes to the G0 phase from G1. In Go which is also known as no gap, a cell stops dividing and remains in the resting phase. For example, nerve cells remain in the G0 phase throughout the life of animals.
Know we discuss the definition and phases of Mitosis.
MITOSIS
DEFINITION
It is the type of cell division in which the numbers of chromosomes in daughter cells remain the same regarding the parent cell.
Mitosis is further divided into 2 phases. (a) Karyokinesis and (b) Cytokinesis.
Let’s discuss karyokinesis and then cytokinesis.
KARYOKIESIS
Karyokinesis is the division of the nucleus which is divided into 4 phases.
Following are the phases of karyokinesis
- PROPHASE.
Normally Mitosis as a whole takes 2.5 to 3 hours to complete, while the Prophase takes 1 hour, so it is the largest phase of Mitosis. In prophase mitotic apparatus appears, spindle fibers are produced and chromosomes come in visible form. Spindle fibers are attached at the centromere of chromosomes. The centromere is the site where chromatids are attached together. The centromere consists of kinetochore protein and spindle fibers join at the kinetochore of the centromere. Condensation starts in prophase.
PRO METAPHASE
This is the division before metaphase. In this phase nuclear envelop and nucleoli disappear.
2. METAPHASE
The Word meta means, middle. This is the phase of mitosis in which the chromosomes arrange themselves in the middle of the cell.
3. ANAPHASE
It is the fourth phase. In this phase, the separation of duplicated genetic material carried in the nucleus of a parent cell into two identical daughters is completed. The separated chromosomes are then pulled by the spindle to opposite poles of the cell. Chromosomes also reach their overall maximum condensation in late anaphase, to help chromosome segregation and the reformation of the nucleus. Anaphase is characterized by two motions. During Anaphase A, chromosomes move to either pole of a dividing cell. The second motion, Anaphase B, involves the separation of these poles from each other.
4. TELOPHASE
This is the last phase of mitosis. This phase is a reversal of the prophase. Nuclear envelop and nucleoli appear. Condensation is near complete. The mitotic spindle is disassembled and the remaining spindle microtubules are depolymerized. Telophase covers approximately 2% of the cell cycle’s duration.
CYTOKINESIS
Cytokinesis is the division of the nucleus. Typically begins before late telophase and, when complete segregates the two daughter nuclei between a pair of separate daughter cells.
Karyokinesis is almost the same in both animal and plant cells, but cytokinesis is totally different in animal and plant cells.
CYTOKINESIS IN ANIMAL CELL
Whether the cell division is mitosis or meiosis, cytokinesis happens in much the same way. Cellular signals tell the cell to divide, which creates the division plane. Around this plane, the cytokinesis furrow will form, eventually pinching off to separate the two cells. The final process of cytokinesis in animal cells is abscission. During abscission, the actin-myosin contractile ring that creates the cytokinesis furrow is contracted all the way, and the plasma membrane undergoes fission to finally separates the two cells.
CYTOKINESIS IN PLANT CELL
Plants are surrounded by a secondary layer, the cell wall, This extracellular structure is responsible for helping to give plants their shape, and must be established when a cell divides. Plants use a microtubule spindle structure known as phragmoplast. The phragmoplast carries vesicles of the cell wall to the new cell plate. After the plate divides the cell, the plasma membrane will seal off, and the two cells will be separated.
TERMS TO KNOW
(A)CONDENSATION (B)MITOTIC APPARATUS (C)ASTER FORMATION
Condensation
Condensation refers to the coiling of chromosomes. Chromosomes as we know consist of histone proteins. All the proteins other than histone protein are negatively charged but due to the presence of two amino acids(lysine and arginine) which are present in abundance histone becomes positively charged. Contrary to this DNA bears a negative charge, so very strong forces of attraction between histone protein and DNA. The DNA hence starts to wrap over histone. The process is so-called which is referred condensation. After coiling supra coiling takes place and chromosomes come into a visible form which is the result of condensation.
MITOTIC APPARATUS
Apparatus as we know deals with any material. All the material which is used in mitosis is mitotic apparatus. For example spindle fiber, centriole, and chromosomes all are mitotic apparatus.
ASTER FORMATION
Aster formation which appears during prophase is the combination of centriole and spindle fibers. Spindle fibers originate from centrioles during prophase.
SIGNIFICANCE OF MITOSIS
In mitosis, the heredity material is equally distributed in the daughter cell. As there is no crossing over or recombination, the genetic information remains unchanged generation after generation, thus continuity of similar information ensures from parent to daughter cell. Some organisms undergo asexual reproduction, Regeneration, healing of wounds, and replacement of older cells are gifts of mitosis. The development and growth of multicellular organisms depend upon orderly controlled mitosis. Tissue culture and cloning seek help through mitosis. For all this, an organism requires managed, controlled, and properly organized process of mitosis, which otherwise may result in malfunctioning, unwanted tumors, and lethal diseases like cancer.