MitosisMitosis

What is the function of mitosis?What is the function of mitosis?

What is the function of mitosis?What is the function of mitosis?

- Growth

- Repair of damage cells

- Asexual reproduction (binary fission, budding and vegetative reproduction)

MitosisMitosis

Mitosis is the process in which a cell duplicates its chromosomes to generate two identical cells. It is generally followed by cytokinesis which divides the cytoplasm and cell membrane. This results in two identical cells with an equal distribution of organelles and other cellular components. Mitosis and cytokinesis jointly define the mitotic (M) phase of the cell cycle.

Mitosis - PhasesMitosis - Phases

- the process of mitotis can be divided into five stages:

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

Prophase Prophase

- at the onset of prophase, chromatin condenses together into a highly ordered structure called a chromosome.

- the replicated chromosomes have two sister chromatids, bound together at the centromere by the cohesion complex. Chromosomes are visible at high magnification through a light microscope.

Prophase Prophase - close to the nucleus are two centrosomes. Each centrosome acts as a coordinating center for the cell's microtubules. The centrosomes are only present in animals. In plants the microtubules form independently.

Prophase Prophase - close to the nucleus are two centrosomes. Each centrosome acts as a coordinating center for the cell's microtubules. The centrosomes are only present in animals. In plants the microtubules form independently.

- the nucleolus breaks down and the mitotic spindle apparatus starts to form.

- the nuclear membrane starts to break down and large organelles are cleared from the central region of the cell.

Allium - late prophase

MetaphaseMetaphase- the chromosomes are now free in the cytoplasm.

- the spindle fibres form a radial array, some of which attach to the centromeres of the chromosomes.

- the chromosomes are maximally contracted and align on a flat plane midway between the poles on the spindle equator (metaphase plate).

AnaphaseAnaphase- the proteins that bind sister chromatids together are cleaved, allowing them to separate. These sister chromatids are hereafter independent sister chromosomes. They are pulled apart by shortening kinetochore microtubules and toward the respective centrosomes to which they are attached.

- this is followed by the elongation of the nonkinetochore microtubules, which pushes the centrosomes (and the set of chromosomes to which they are attached) apart to opposite ends of the cell.

Allium – early anaphase

TelophaseTelophase- At telophase, the nonkinetochore microtubules continue to lengthen, elongating the cell even more.

- Corresponding sister chromosomes attach at opposite ends of the cell.

- A new nuclear envelope, using fragments of the parent cell's nuclear membrane, forms around each set of separated sister chromosomes.

- Both sets of chromosomes, now surrounded by new nuclei, unfold back into chromatin.

Allium – telophase

CytokinensisCytokinensis- cytokinesis is a separate process that begins after telophase.

- cytokinesis is technically not even a phase of mitosis, but rather a separate process, necessary for completing cell division.

- in animal cells, a cleavage furrow (pinch) containing a contractile ring develops where the metaphase plate used to be, pinching off the separated nuclei.

CytokinensisCytokinensis

- in plant cells, a cell plate forms between daughter cells. After the cell plate is formed, walls of cellulose are deposited on either side.

Importance of MitosisImportance of Mitosis

each new daughter cell receives the same number and kind of chromosomes as the mother cell; daughter cell are genetically identical to their mother cell and to each other.

Mitotic IndexMitotic Index

Mitotic index is a measure for the proliferation status of a cell population. It is defined as the ratio between the number of cells in mitosis and the total number of cells.

number of cells in mitosis

total number of cells Mitotic index =