Mitosis and the cell cycle (3.10)
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Not all eukaryotic cells retain the ability to divide, but those that can undergo the cell cycle, a series of stages involving growth and division. The outcome is two genetically identical daughter cells.
The cycle consists of interphase, followed by mitosis and cytokinesis (cytoplasmic division).
Interphase is the stage during which the cell grows and prepares for division. It occupies approximately 90 of the cell cycle, but the length of interphase differs by cell type, owing to the variable length of the G1 phase.
Interphase consists of three phases:
- G1 (first gap)
- S (DNA synthesis)
- G2 (second gap).
During interphase, a cell’s nucleus contains nucleoli (where ribosomes are made) and chromosomes (DNA associated with proteins).
The chromosomes unravel, allowing genes to be transcribed and proteins to be synthesised. Organelles and other cellular components are synthesised (during S phase of interphase) as the cell grows, prepares for division and DNA is replicated
This ensures sufficient cell contents are available to be distributed between two genetically identical daughter cells.
Mitosis is the nuclear division process during which a eukaryotic cell separates its duplicated chromosomes into two identical nuclei. It consists of prophase, metaphase, anaphase and telophase and is followed by cytokinesis.
Cytokinesis is the division of the cytoplasm following nuclear division, resulting in the formation of two daughter cells.
Prophase is the first stage of mitosis. Chromatin condenses into chromosomes, each consisting of two sister chromatids joined at the centromere.
The nuclear envelope breaks down and the nucleolus disappears.
Centrosomes (centrioles) move to opposite poles of the cell, forming spindle fibres that guide chromosome movement.
During metaphase, chromosomes align at the cell equator, also called the metaphase plate.
Spindle fibres from opposite poles attach to each centromere.
During the anaphase, the centromeres divide, allowing sister chromatids to separate.
The spindle fibres shorten, moving the chromatids towards opposite poles of the cell.
During telophase, the chromatids are at the cell’s poles and are now chromosomes. The nuclear envelope reforms around each set of chromosomes, creating two nuclei.
The chromosomes uncoil back into chromatin, and the nucleolus is formed.
The mitotic spindle breaks down as the cell prepares for cytokinesis.
Cytoplasmic division (or cytokinesis) is the final stage of the cell cycle where the cytoplasm, cell membrane and organelles divide, resulting in two daughter cells.
- In animal cells, protein filaments in the cell membrane contract, forming a cleavage furrow, until the cell splits in two.
- In plant cells, a new cell plate forms along the cell’s equator, dividing the cell into two. New sections of the cell wall then form.
Mitosis is the process by which a cell divides to produce two genetically identical daughter cells.
This process is vital for asexual reproduction, growth and repair of tissue in plants, fungi and animals.