The cell cycle and stages of mitosis

In a nutshell

Mitosis is the process of separating genetic information to produce new cells. One cell becomes two, two cells become four, four cells become eight (and so on) and all the cells are identical to each other. Mitosis is needed particularly for growth of new tissue through the production of new cells or repair of damaged tissue through the replacement of damaged or dead cells. There are several stages to mitosis that should be known.

The cell cycle

A cell goes through many changes such as growth and division, this is known as the cell cycle. There are three stages to the cell division process: interphase, mitosis and cytokinesis.

Interphase

This is where replication of the cell contents occurs. From each structure such as mitochondria and ribosomes to even the amount of cytoplasm; everything is doubled. Most importantly, the chromosomes in DNA are all replicated in this stage. Overall, the cell doubles in mass.

Mitosis

This is where the separation of genetic information occurs. While the cell hasn't divided just yet, the cell contents can be organised in two groups to make cell division easier.

Cytokinesis

At this stage, the cell membrane splits so that all the cell contents are divided between two daughter cells that are genetically identical to each other. This is known as cell division. The number of cells produced after several cell cycles can be known as $2^n$ where $n$ is the number of cell divisions that have occurred.

Example

How many cells will be produced after $5$ cell divisions? Each cell division produces two cells.

Put into formula:

$2^5=32$ 

$\underline{Therefore,\ after\ 5\ cell\ divisions\ there\ will\ be\ 32\ cells.}$

Biology; Cells and control; KS4 Year 10; The cell cycle and stages of mitosis — This piechart shows the three stages of the cell cycle: 1. Interphase, 2. Mitosis, 3. Cytokinesis.

The stages of mitosis

The stages of mitosis are as follows.

STAGE	DESCRIPTION
Prophase	After DNA has been replicated in interphase, the chromosomes condense and the membrane around the nucleus breaks down. This makes the chromosomes visible under the microscope.
Metaphase	All the chromosomes and their copies line up at the equator (the middle of the cell).
Anaphase	Spindle fibres start forming at two opposite ends of the cell and pull apart the chromosomes to opposite ends of the cell.
Telophase	The spindle fibres detach so that the chromosomes are in opposite ends of the cell. The membrane of the nucleus reforms around the chromosomes and the chromosomes decondense. The rest of the contents of the cell are also at opposite ends of the cell so that they are prepared for the dividing of the cell which is known as cytokinesis.

Note: DNA replication and cell division are not stages in mitosis. DNA replication is needed for mitosis to occur, and cell division happens as a result of the mitosis process; however they are separate things.

Biology; Cells and control; KS4 Year 10; The cell cycle and stages of mitosis

1.	Interphase
2.	Mitosis occurs with its four stages (prophase, metaphase, anaphase and telophase)
3.	Cell division occurs to produce two identical daughter cells.

Mitosis and growth

Mitosis is important for growth and repair. Once mitosis has occurred and a genetically identical cell is produced, the cell can then differentiate into another type of cell needed for growth. Cell differentiation is how cells change to develop features specific to its function.

In animals, this ability to differentiate is lost early - so cell division in adults will only produce identical cells. Cell division happens at a fast rate when animals are young to produce lots of new cells for growth and reduces when animals are older, with new cells mainly being produced to replace damaged cells and repair tissues.

In plants, the ability to differentiate is retained in adulthood, so a cell can divide and differentiate to produce more cells of different types. The rate of cell division in plants will also slow down with time, but not to the extent that is seen in animals. This results in plants being able to develop new parts such as branches and leaves to continue growing throughout its lifetime. Plants can grow using mitosis, but also by utilising cell elongation, where the cells expand and become bigger, which allows the plant to grow in height.

Mitosis gone wrong

While mitosis is important in growth and repair, sometimes it can become uncontrolled so that cells keep dividing. The uncontrolled cell division is also called cancer. The cells from this uncontrolled division group together to form a tumour.