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Topic 3: Voice of the genome›Mitosis and the cell cycle (3.10)

Mitosis and the cell cycle (3.10)

An overview of mitosis and the cell cycle (3.10) from Edexcel A level Biology A

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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).

The image depicts a circular diagram representing the cell cycle. The outer circle is labeled with two main phases: 'I (Interphase)' on the left in blue and 'M (Mitotic phase)' on the right in purple, with arrows indicating the direction of the cycle. The inner circle is divided into segments labeled 'G1' in green, 'S' in pink, 'G2' in brown, 'M' in yellow, and a small gray segment labeled 'Cytokinesis.' An additional green arrow curves into 'G1' from a segment labeled 'G0 Resting.'

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).

Diagram of a cell structure with labeled components. The diagram shows a large circular shape representing the cell. Inside is a smaller circle labeled 'Nucleus.' Within the nucleus, there's a densely packed area labeled 'Nucleolus' and a tangled network labeled 'Chromatin.' The nucleus is surrounded by a thin line labeled 'Nuclear envelope.' Outside the nucleus, near the top, there is a structure with a sunburst-like appearance labeled 'Centriole.'

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.

Diagram showing stages of cell division: Interphase with tangled chromatin, Prophase with condensed chromosomes, Metaphase with chromosomes aligned at the center, Anaphase with separated chromosomes moving to poles, Telophase with two distinct nuclei forming, and Cytokinesis with two separate cells. Each stage is labeled accordingly.

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.

The image shows two diagrams labeled 'Early prophase' and 'Late prophase'. In the 'Early prophase' diagram, there are two centrioles with spindle fibers extending from them, positioned outside a nucleus. Inside the nucleus, labeled structures include the nucleolus, and several chromosomes depicted as pairs of connected blue and red lines. The nuclear envelope surrounds the nucleus. The 'Late prophase' diagram shows spindle fibers extending from centrioles towards the center where chromosomes, depicted as red and blue paired lines, are more condensed and aligned. Labels indicate the chromosomes and spindle fibers, with the centrioles positioned at opposite poles.

During metaphase, chromosomes align at the cell equator, also called the metaphase plate.

Spindle fibres from opposite poles attach to each centromere.

Diagram labeled 'Metaphase' showing a cell with a light blue circular background. In the center, blue and red structures labeled 'Chromosomes' are aligned vertically. Each chromosome has a central black dot labeled 'Centromere.' Gold lines extend from the centromeres to structures labeled 'Centriole' at each end of the cell. These lines are labeled 'Spindle fibres.' The entire cell is labeled 'Cytoplasm.'

During the anaphase, the centromeres divide, allowing sister chromatids to separate.

The spindle fibres shorten, moving the chromatids towards opposite poles of the cell.

The image illustrates the anaphase stage of cell division. Inside a blue circle representing the cytoplasm, two groups of chromatids, depicted as red and blue curved lines, are being pulled apart toward opposite sides. Each group is connected to a centriole, represented as a yellow structure with radiating lines, located on either side of the circle. Labels indicate 'Chromatids' pointing to the red and blue structures, 'Centriole' pointing to the yellow structure, and 'Cytoplasm' pointing to the blue circle. The word 'Anaphase' is written at the top of the image.

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.

The image illustrates the telophase stage of cell division, showing two circular cells connected in the center. Each cell contains a labeled centriole with radiating spindle fibers. Inside each cell, a nuclear envelope encloses chromatids, depicted as red and blue curved lines, some connected by black dots. Labels include 'Centriole', 'Chromatids', 'Nuclear envelope', 'Nucleolus', and 'Cytoplasm'. The title 'Telophase' is centered at the top of the image. The copyright notice '© Medify' is at the bottom center.

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.

Illustration comparing animal and plant cell division. On the left, labeled 'Animal cell', three stages of cell division are shown. The top stage depicts two connected cells with a dashed line labeled 'Cleavage furrow'. The middle stage shows two separate cells, each with visible organelles, including red and blue structures and a purple dot. The bottom stage shows two fully separated cells. On the right, labeled 'Plant cell', three stages of cell division are depicted. The top stage shows two connected cells with a dashed line labeled 'Cell plate'. The middle stage shows two adjacent cells with a solid line between them. The bottom stage shows two separated cells, each with similar organelles as in the animal cell diagram.

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.