Cells constantly need to divide, both during our development and growth, and to replace damaged or dead cells. The purpose of mitosis is to produce two genetically identical nuclei. The cell then splits into two cells during cytokinesis.

Mitosis consists of 4 subphases:

PROPHASE
METAPHASE
ANAPHASE
TELOPHASE

1. In prophase the replicated DNA is wrapped around proteins called histones to form visible chromosomes. These consist of two identical (sister) chromatids joined at a centromere. The nuclear envelope breaks down, and spindle fibres form a structure called a spindle.

2. In metaphase the chromosomes reach the centre (or "equator") of the cell. At this point the chromatids are still held together.

3. In anaphase, the sister chromatids split and begin to move towards opposite ends (poles) of the spindle. Since one identical
copy of each chromosome ends up in one daughter cell, the cells are identical to each other and to the original cell.

4. In telophase, the separated chromatids (now called chromosomes) reach the poles of the spindle. The spindle breaks down,
and two nuclear envelopes form, one around each set of chromosomes. Thus, two distinct, identical nuclei are formed.

	Created by Stephen Cole over 10 years ago

A-Level Biology (Cell Cycle and Cell Division (unit 2)) Note on Cell Cycle and Cell Division, created by Stephen Cole on 25/04/2014.