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Mitosis and the Cell Cycle
- Mitosis is the process in which two genetically identical daughter cells are produced form one parent cell nucleus.
- This process is divided into 6 stages which occur in the following order:
- Interphase - Prophase - Metaphase - Anaphase - Telophase - Cytokinesis
- Below I will go into more detail about each individual stage and what occurs during it.
Most Eukaryotic cells spend the majority of their time in this phase.
During interphase there are 3 separate stages:
- During this stage the cell 'grows' and a lot of protein synthesis occurs.
- The chromosomes are all unreplicated and each contains only one molecule of DNA.
- This is the period when the cell replicates its DNA
- Once this stage has been completed all of the chromosomes have two chromatids.
- Growth continues and the organelles replicate in preparation for the cell to divide during mitosis.
- The proteins necessary for cell division (such as those that form the microtubules/spindle fibres) are produced.
- In prophase the chromosomes shorten and thicken and become visible under a light microscope.
- The nuclear envelope breaks down and disappears.
- The centriole (an organelle in the cell) divides into two and each part moves to different poles of the cell to form the spindle.
- The centrioles are made of protein threads.
- The pairs of homologous chromosomes are now as tightly coiled and condensed as they will be in meiosis.
- The chromosomes move to the central region of the spindle (equator).
- The chromosomes become attached to the spindle thread by its centromere.
- The centromere is the part of the chromosome that links the sister chromatids.
- In this stage the centromere that holds together the sister chromatids split.
- This effectively makes each 'sister' chromatid an individual chromosome.
- Both chromosomes are identical to each other an and the parent cell from which it was copied.
- The spindle fibres that are attached to the chromosomes shorten and pull the chromosomes towards the opposite poles of the cell.
Telophase and Cytokinesis
- As the separated chromosomes reach the opposite poles of the cell a new nuclear envelope forms around each set.
- The spindle breaks down and disappears.
- The chromosomes uncoil and once again become not visible under the light microscope.
- The whole cell splits into two to form two new cells containing full sets of chromosomes, this is called cytokinesis.