MITOSIS

Mitosis is the name for the way that a cell duplicates itself so that each daughter cell receives an identical copy of its genetic material. So, at the end of mitosis, there will be two identical cells instead of one.

The events that occur differ in prokaryotes and in eukaryotes.

The normal state of a cell is known as the interphase. A normal eukaryotic cell has 1 set of chromosomes. During this phase, DNA is being replicated. 

Interphase

At the end of interphase, the amount of DNA will be twice the normal amount. Thus, the cell will have 2 sets of chromosomes.

The act of cell division can be broken down into 4 'phases'. They are the prophase, metaphase, anaphase and telophase.

1. Prophase

Early Prophase

This is the first stage of cell division. Here, the cell prepares itself for division. The nucleus swells, and chromosomes become visible. Each chromosome has two chromatids (genetic thread from winded chromosomes) as a result of duplication of the DNA which took place during interphase. The two chromatids are linked together at a centromere. The centrosome (2 centrioles) duplicates into 2 diplosomes, and each diplosome, or aster moves toward opposite poles of the nucleus.

Late Prophase

2. Metaphase

Metaphase

Microtubules assemble, and form a network (the spindle fibres). The chromosomes move towards the equator of the cell, where they are visible. This is the phase in which morphological studies of chromosomes are carried out, often for clinical purposes.

3. Anaphase

Early Anaphase

The two sister chromatids separate. Each one goes to opposite ends of the cell, so each daughter cell has an identical complement of chromosomes . The nuclear membrane has disappeared at this stage. The cell membrane expands as the cell elongates. The diameter of the cell decreases at the equator.

Late Anaphase

4. Telophase

Telophase

A new membrane forms around the new nuclei and two cells are quickly formed. The chromatid, now called a chromosome, uncoils, and the nucleolus becomes visible again. Each cell has 2 set of chromosomes.

What triggers mitosis?

External signals, hormones, internal factors, growth factors (proteins able to trigger mitosis): these proteins have a receptor on the cell membrane. When the protein is attached to the receptor, it triggers several events in the cell that end with the division of the cell.

When does a cell become cancerous?
It becomes cancerous when it loses the ability to stop dividing when encountering another cell (hence the formation of a tumour), or when it becomes immortal.