Mitosis and the Cell Cycle

The Cell Cycle

Most cells in the body go through a cell cycle. This cycle is tightly controlled and it has four stages.

A diagram of the cell cycle showing the four stages; G1 Phase, S Phase, G2 Phase, and M Phase

  • G1 Phase – Gap Phase 1: Every sub-cellular structure (organelle) within the cell is doubled (except chromosomes).
  • S Phase – Synthesis: The DNA replicates to form two copies of each chromosome. Within the cell, each of the 23 pairs of chromosomes is duplicated, leading to 46 duplicated chromosomes.
  • G2 Phase – Gap Phase 2: Chromosomes within the cell are checked for errors to ensure that no errors are passed down to daughter cells.
  • M Phase Mitosis: In this stage, the cell divides into two identical daughter cells.

Mitosis is the final stage of the cell cycle.

Calculating the length of stages in the cell cycle

We can use this formula to calculate the length of different stages of the cell cycle:

Calculating the different stages of the cell cycle - Length of time in stage is the observed number of cells in the stage divide by the total number of cells observed, multiplied by the total length of cell cycle

So, to calculate the length of time a cell spends in a specific stage, divide the observed number of cells in that stage by the total number of cells observed. Then, multiply this by the total length of the cell cycle.

Mitosis

Mitosis is a type of cell division that produces two identical diploid daughter cells. The daughter cells produced from mitosis are clones of each other, which means their DNA is identical.

They are also genetically identical to the parent cell. This way all your cells have an identical DNA composition.

REMEMBER! There are 23 pairs of chromosomes in each cell of the body

Stages of mitosis

The stages of mitosis are prophase, metaphase, anaphase and telophase.

Interphase – This phase must happen before Mitosis begins. G1, S and G2 stages of the cell cycle occur during interphase. The cell spends most of its life in this phase. Before mitosis can produce two diploid cells from one, the DNA in chromosomes must replicate. This ensures that chromosome numbers remain consistent after cell division

1. Prophase – The chromosomes and their copies condense to become more visible. Also, the membrane around the nucleus disappears.

2. Metaphase – Chromosomes and their copies line up in the middle of the cell.

3. Anaphase – Chromosomes and their copies are pulled to different ends of the cell.

4. Telophase – New membranes form around the chromosomes at each end of the cell. The cell membrane pinches in and eventually divides into two daughter cells, which is called cytokinesis.

A diagram showing the four stages of Mitosis: Prophase, metaphase, anaphase, and telophase

Mitosis is continuously occurring throughout our bodies.

Why does Mitosis occur?

Mitosis produces new cells and replaces cells that are old, lost or damaged. For you to stay alive and fully functional, these cells need to be continuously replaced. Mitosis is the reason we can grow, heal wounds, and replace damaged cells.

Mitosis is responsible for:

  • Growth for multicellular organisms
  • Repair of damaged tissues
  • Replacement of cells
  • Asexual reproduction in single-celled organisms like amoeba, and it also occurs in some plants.

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