3.24 - Mitosis

a) Outline/summary
number or chromosomes in neucleus = diploid number (2n)
in humans 2n=46
in cats 2n=38
In the process of mitosis a cell divides into 2 identical cells:
                        -they have the same number of chromosomes
                        -same set of chromosomes
Each new cell has a diploid nucleus


b) Details
Copying the chromosomes is a process called DNA replication
-Each chromosome undergoes a copying process to form an identical copy of itself (same genes)
-These 2 copies are held together by the structure around the centre region, know as the centromere
-These are known as a pair of chromatids
-The process (DNA replication) takes place in the nucleus (the process cant be seen because the nucleus stays intact). this is know as the interphase


c) Stages of mitosis
We would normally see that the nucleus has a spherical structure if we looked at it down a microscope and we would be unable to see the chromosomes.
It is during that interface that DNA replication occurs
Prophase- The membrane breaks down and the chromosomes (pair of chromatids) can be seen. each chromosome got copied

The nucleus is gone and there is a network of protein molecules inside the cell called a spindle
-These go from one pole of a cell to the other
-The pair of chromatids will join on one of the spindles fibres at the centromere

Metaphase: When the pair of chromatids are attached to a spindle fibre by the centrometer
-The chromatid is in the middle across the equator of the cell

Anaphase: the spindle fibre shortens pulling one chromatid in one direction and the other chromatid in the other direction. This pulls the chromatides to the poles of the cell.
-This seperated the chromatids

Telophase: Nucleus begins to reform around the chromosomes at either end of the cells (new nucleus of the new cell)
We see the formation of 2 nuclei at opposite ends of the cell

Cytokinesis: The cell splits into 2 (not a part of mitosis)