Mitosis is a process of indirect division of somatic eukaryotic cells, as a result of which two daughter cells with the same set of chromosomes are formed from one diploid mother cell.
Cell preparation for mitosis occurs in the interphase: DNA doubles, ATP accumulates, fission spindle proteins are synthesized, centrioles are doubled.
Mitosis involves two processes: karyokinesis (division of the nucleus) and cytokinesis (division of the cytoplasm).
There are four phases of mitosis: prophase, metaphase, anaphase and telophase.
In division schemes, the haploid set of chromosomes is denoted by the letter n, and DNA molecules (i.e., chromatids) by the letter c. Before the letters indicate the number of haploid sets:
- 1n2с – haploid set of doubled chromosomes,
- 2n2с – diploid set of single chromosomes,
- 2n4с – diploid set of doubled chromosomes.
Example: in human cells, the haploid set consists of 23 chromosomes. This means that the notation 2n2с means 46 chromosomes and 46 chromatids, and 2n4с – 46 chromosomes and 92 chromatids, etc.
In the nucleus, DNA molecules shorten and twist (spiralize) to form compact chromosomes.
Each chromosome consists of two DNA molecules (two chromatids) connected by a centromere.
The nuclear envelope is disintegrating.
Chromosomes are disordered in the cytoplasm.
The nucleoli dissolve.
The spindle of division begins to form, some of the filaments of which are attached to the centromeres of the chromosomes.
Centrioles begin to disperse in the animal cell.
Chromosomes are located at the equator of the cell, forming a metaphase plate.
Chromatids are connected in the area of the primary constriction with the fission spindle filaments.
The centrioles are located at the poles of the cell.
Each chromosome, made up of two chromatids, splits into two identical daughter chromosomes.
Daughter chromosomes are stretched by the dividing spindle filaments to the poles of the cell.
Each pole has the same genetic material.
The chromosomes unwind.
Nuclear membranes begin to form around the chromosomes.
Nucleoli appear in the nuclei.
The spindle threads are destroyed.
This is where karyokinesis ends. Cytokinesis occurs – division of the cytoplasm
1 – prophase, 2 – metaphase, 3 – anaphase, 4 – telophase
The biological significance of mitosis
As a result of mitosis, genetically identical daughter cells are formed with the same set of chromosomes that the mother cell had. Continuity is maintained in a number of cell generations.