Mitosis
Cells reproduce through a continuous sequence of growth and division known as
the cell cycle.
The cell cycle consists of 2 main stages:
1)Growth (Interphase)
2) Division (Mitosis)
During Interphase, the cell makes new molecules which increase the cell’s
volume and mass. DNA is copied during this stage.
The division stage involves two processes; mitosis (division of the nucleus) and
cytokinesis (division of the cytoplasm)
Mitosis, although continuous, is divided in to four phases characterized by a
particular arrangement of the chromosomes within the cell and by the
appearance or disappearance of other cell structures.
Prophase
Prophase is the first phase of mitosis.
During prophase the chromatin coils into chromosomes.
The nuclear membrane and nucleolus disappear.
Centrioles migrate to the poles of the cell and spindle fibres begin to form.
Metaphase
Metaphase is the second phase of mitosis.
The spindle fibres attach to the centromeres of the replicated chromosomes.
The chromosomes are guided by the spindle fibres to the centre of the cell.
Anaphase
Anaphase is the third phase of mitosis.
The centromere splits apart and the chromatids are pulled to opposite poles by
the spindle fibres shortening.
Telophase
Telophase is the fourth phase of mitosis.
The chromatids have reached the poles of the cell and begin to unwind and
become less visible.
Spindle fibres break down and disappear.
The nucleolus reappears and the nuclear membrane begins to form around each
set of genetic information at the poles.
Cytokinesis
Cytokinesis is the final separation of the cytoplasm and the formation of two new
daughter cells.
In animal cells an indentation of the membrane surrounding the two cells forms
and deepens. This is called a cleavage furrow.
In plant cells a cell wall and membrane form to separate the two daughter cells.
This is called a cell plate.