Mitosis The Cell Cycle

The cell cycle, or also known as the mitotic cell cycle, is key in an organisms life in order to sustain life. It's important to know the reasons why mitosis is important:

• To allow dead cells to be replaced
• Growth and repair of new tissues
• Asexual reproduction
• To maintain the chromosome number in every cell

Thought this would be a perfect play
on words (Source; Haiden, Unsplash) 

By definition, mitosis is a type of cell division that produces two genetically identical  daughter cells from a parent cell. But what happens before mitosis occurs?

Anything that happens before mitosis occurs is in the interphase; this is where the cell prepares to undergo mitosis (cell division). The checks during interphase are vital as if an error is detected, the cell must be terminated. This is why the highest number of cells can be observed at the beginning of interphase as it's likely that up to 5% of cells will be terminated during different stages of interphase (after failing to meet checkpoint requirements)

1. At the start of the cycle, the cell will be in G1 phase where the cell will grow and organelles in the cell will replicate so that each of the daughter cells has the same number of organelles.
2. After G1 , there is a checkpoint to ensure the cell is ready to enter the next phase
3. The next stage is the S phase where DNA replication occurs. In short, the chromosome will now be formed from 2 sister chromatids. This process happens rapidly to reduce the chance of mutations.
4. The cell next enters the G2 phase which is where it continues to grow.
5. At the end of the G2 phase, there is the G2 /M checkpoint to ensure the cell is ready to undergo mitosis
6. Alternatively, the cell may not enter the G1 phase and will enter the G0 phase where the cell doesn't undergo the other processes. This can be for a number of reasons;

• Apoptosis (the cell may be purposely terminated)
• Differentiation;  the cell may differentiate to become specialised instead of undergoing mitosis
• Some cells may take a very long time/ never enter the interphase e.g nerve cells (in order to store memory!)

The cell cycle

After interphase, the cell begins to undergo mitosis. There are four main stages in mitosis to learn;

• Prophase; the DNA supercoils (thickens and shortens, becoming visable) and the nuclear membrane breaks down
• Metaphase; the chromosomes make their way to the equator and line up on spindle fibres (one per spindle) 
• Anaphase; the spindle fibres (with the aid of motor proteins) pull the genetically identical sister chromatids from the chromosome to opposite poles of the cell
• Telophase; the nuclear membrane reforms around the two poles as the cell prepares to split

After these four stages, cytokinesis occurs meaning the cell splits into the two genetically identical daughter cells.