CONCEPT OF MITOSIS Plants and animals are known to undergo sexual reproduction. Sexual reproduction results in the formation of single cells calledZygotes. This zygote is made up of million of cells and must develop. Therefore these single cells must divide many times in order for thezygote to grow and develop into an adult. This type of cell division that takes place is known as Mitosis. Mitosis can therefore be defined as a process where by one celldivides to form two cells that are identical to each other and theparent cell which the two cells come from Therefor only body or sometic cells undergo mitosis.(somatic cellsare all cell other than sex cell)
CHROMOSOMES Chromosomes are formed when the chromatin network, which issituated in the nucleus, coils up, thickens and shorten. Chromosomes are known to be made up of DNA, and DNA contains the genetic code for controlling the appearanceand function of thousands of cells. Different organisms are known to have different number ofchromosomes. Humans therefore have 46 chromosomes (23 pairs) They are also arranged in identical pairs. One chromosome consist of 2 chromatids and only one centromerethat attach the two chromatids together. Chromosomes are known to be visible only during cell division.
WHY IS MITOSIS IMPORTANT?Reproduction in some simple organisms.Repairing of damaged cells/tissues.Replacing of dead cells/tissues.Mitosis allows organisms to grow.
THE CELL CYCLEMitosis refers to the division of the nucleus onlyinto two nuclei, therefore interphase andcytokinesis are not part of the process of mitosis.The cell cycle is therefore:Interphase(this includes G1,S-[DNA synthesis] andG2phase.Mitosis.CytokinesisGrowthThis results in the formation of two identical cells.
THE PROCESS OF MITOSISConsist of the following phases:InterphaseProphaseMetaphaseAnaphaseTelophase
INTERPHASE• In this phase, the cell prepares for cell division,this is by building up enough energy.• The DNA replicates(doubles) itself, so that thegenetic material is double.
PROPHASEThe nuclear envelop and nucleolus disappears.The chromatin network becomes tight and then coilsup and is now visible as chromosomes.Chromosomes now arrange randomly within the cellCentrioles move to the opposite ends with spindlefibres between them.
METAPHASEThe chromosomes arrange themselves randomlyalong the equator of the cell, each are attached to aspindle fibre.The centriole have now finally reached the oppositepoles, attached to the chromosomes by means of aspindle fibres to the centromere.
ANAPHASE• Spindle fibres now pulls tight , thus splitting thechromosomes into two chromatids splits into two.• The centromere that attaches the two chromatidsalso splits into two.• The two daughter chromosomes then move to theopposite poles
TELOPHASE• Now two groups of chromosomes occur, the occur atopposite ends.• The nucleus envelop now surrounds thechromosomes at the opposite poles.• Nucleolus now reappears at each poles.• The chromosomes now become less dense and noware visible as chromatin network
LATE TELOPHASE• Invagination of the cytoplasm and the plasmaoccurs.• This then goes on until the cell has totallydivided into two separate identical cells.