Interphase - Normal state of all cells. Chromosomes are not yet visible. During this stage cells carries out synthesis (growth) of cytoplasm and organelles such as mitochondria, enzymes and it increases in size. DNA replication also takes place in this stage so each chromosome consists of a pair of chromatids.
Prophase - Chromosomes become visible as chromatin fibres shorten and thicken by spiralisation. This condensation of chromosomes takes place. Once chromosomes are clearly visible they can be seen to consist of two chromatids. They have the same size and has an identical DNA base sequence.
Late prophase - 2 chromatids are twisted around one another and joined together by a centromere. The centrioles migrate to oppose ends of the cell and mictotubules develop to form fibres. The fibres make up a structure aka spindle. The spindle runs from pole to pole but is broadest at equator. Nucleolus disappears and finally the nuclear membrane breaks down.
Metaphase - Chromosomes line up at the equator of the spindle. Thy become attached to the spindle at their centromeres and line up across the equator
Anaphase - The centromeres divide into two and the spindle fibres pull the daughter centromeres apt. The separated chromatids are pulled along behind the centromeres. once separated the sister chromatids should now be called chromosomes and are now drawn to opposite poles.
Telophase - Chromosomes reach poles of the cell's spindle. The nuclear membrane reforms around each of the two groups of chromosomes and the nucleoli re-appears. The spindle fibres disintegrate and centrioles replicate Prophase coiling sequence is reversed so that as the chromosomes uncoils and lengthen they cannot be seen clearly.
CYTOKINESIS - Telophase leads into cytokinesis (division of cytoplasm) so that daughter cells are formed. Cytokines differs in plant and animal cells. Animals undergo cleavage by constriction of the cytoplasm and furrowing the plasma membrane in plants a cell plate forms across the equator.
(Plants) - In animals most cells are capables f cytokinesis whereas in plants only special cells aka meristems can divide in this way. They are found at the root and shoot tips. Meristem tissues are responsible for the growth of the whole organism. Plants cells that do not have centrioles the tubulin protein threads are made in the cytoplasm
(Animals) - In animals cells cytokinesis starts from outside working inwards to the cell membrane but in pants cells it starts with the formation of the cell plate where the spindle equator was. New cell mebrane and new cell was material is laid down along this cell plate.
Yeast cells undergo cytokinesis by producing a small bud that nips of the cell, in a process called budding.
ROLL OF MITOSIS
- Asexual reproduction e.g. propagation in plants
- Growth - of multicelluar organsims by producing extra cells.
- Replacement - e.g. RBC and skin cells are replaced by new ones.
- Repair - damaged cells that needs to be replaced by identical new ones.
Features of mitosis: chromosome number is maintained there is no change in genetic material.
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