How Do Cells Divide?

Mitosis is where a cell will duplicate its contents including its genes and distribute them to two daughter cells. In unicellular micro-organisms it serves to increase the amount of individuals of the population. In plants and animals it is the mechanism by which the organisms grow from one single cell into an entity with multiple complex organs. As such, the basic genetics of cell division is tightly controlled and regulated, as aberrant growth patterns result in many diseases.

Cell Cycle
Cells start to grow, assimilating nutrients from their environment and synthesizing new structural components, as they need them. This process continues until the cell gets to a critical point where it starts to divide. The cell then divides into two cells, which start to grow again. New cells are structurally and functionally similar to the mother cell, their basic genetics are the same, though some changes can occur if genetic mutations spontaneously appear.

Any cell goes through alternate periods of regular growth and cellular division, a process known as the cell cycle. The non-divisional period of the cell, known as interphase precedes the actual cell division, which can be divided into two processes: mitosis (nucleus division) and cytokinesis (division of the non-nuclear material).

Phases of Mitosis
Mitosis can be divided, for the sake of clarity, into various phases:

Interphase
Technically speaking this is where the cell is preparing for cell division. The cell is metabolically active. Under a light microscope, chromosomes cannot be seen inside the nucleus since the chromatin material is dispersed.

Prophase
This is where the cell starts to divide. In prophase, chromatin (previously unseen) starts to congregate in the nucleus and become visible. The nucleolus (an organelle) disappears and centrioles start to move to opposite sides of the cell. Fibers start to appear from the centromeres.

Prometaphase
In this phase the nuclear membrane disappears. Proteins attach to the centromeres creating structures known as kinetochores. Microtubular structures attach at the kinetochores and start to pull the chromosomes and they start to move.

Metaphase
Chromosomes align along the middle of the cell on an imaginary line known as the metaphase plate. This arrangement in the metaphase stage allows the future cells to receive an exact copy of each chromosome when the cell divides.

Anaphase
In anaphase the paired chromosomes move to opposite sides of the cell. The motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules.

Telophase
When chromatids arrive at the cell opposite ends a membrane forms around them and a new nuclear membrane appears forming the nucleus of each daughter cell. Chromosomes start to disperse and become invisible again (under a light microscope). Microtubules and fibers disappear, and the endoplasm (non nuclear material) may start to divide in a process known as cytokinesis.

Cytokinesis
The mechanism of cytokinesis is characteristic of each type of organism. For example, vegetable cells start to build up a cell wall around the cell plate to separate the two daughter cells. In animal cells, a fiber ring around the center of the cell "cuts" the mother cell into two new daughter cells

Basis of Life
As a consequence of this complex process of cell division, DNA material has "passed" from mother to daughter cells in a never-ending process that constitutes the basis of life, as we know it