Mitosis
Joanna George-Johnson, Contributor

Have you ever wondered how it is that we grow? If cells are constantly dying, why are we still alive?

All of this can be explained by the process of mitosis. This article takes you through the process of mitosis and by the end, you should be able to describe how mitosis occurs, its importance and its role in asexual reproduction.

Mitosis is often confused with meiosis, however, they are two different processes.

Mitosis can be defined as the process by which the cell's nucleus replicates and divides, ultimately dividing the cells with a process called cytokenisis.

This results in the production of two daughter cells from a single parent cell. The daughter cells are genetically identical to each other and to the original parent cell, which is vital to sustain the functioning of the cells.

Mitosis is a part of the cell cycle. This is key to understanding how a cell is formed, grows and how it replicates. Below is a diagram of the cell cycle.

Most human cells contain 46 chromosomes and during mitosis, the chromosomes are replicated. One can appreciate that it is on chromosomes that our DNA are found, hence, our genetic material. These control and dictate all the activities of the cells. Mitosis ensures that when cells divide, each daughter cell will have a complete set of chromosomes. Here is how it happens: The chromosomes in the cells produce an exact copy of themselves and the now 'twin chromosomes' are called chromatids, which are joined somewhere in the middle by a centromere. The nucleus then disappears, and then the twin chromosomes line up along the equator (middle) of the cell.

The chromatids are then pulled to opposite sides of the cell by centrioles (tiny structures on opposite poles of the cell during mitosis); the nuclear envelope reforms around each set of chromosomes at each end of the cell. The cells then split along the middle and two genetically identical cells are produced. Thus, the key feature of a cell that allows it to undergo mitosis is the presence of a nucleus.

Mitosis is very important for various reasons, including:

• Cellular replacement
• Tissue repair
• Growth
• Asexual reproduction

The growth and division of cells (mitosis) are important for almost all organisms, including humans. We all began as a single cell that resulted from our father's sperm fertilising our mother's egg. This single cell then divided by mitosis into two cells (daughter cells) which then grew and divided into four cells. This process of mitosis continued from birth and will continue when we are adults. It is still happening right now as some of our cells use mitosis to replace old dead cells, such as skin cells.

Mitosis is also very important in the process of asexual reproduction. This is where one parent cell produces two identical daughter cells. Since mitosis produces identical daughter cells, it is therefore suitable for the process of asexual reproduction. Examples of this are vegetative propagation, budding and binary fission.

The diagram below summarises the process of mitosis. Questions

1. Give the name of two types of human cells that do not undergo mitosis.

2. What is the number of chromatids in a normal human cell during the first stage of mitosis?

3. Define the following terms: chromatids, centromere, cytokinesis.

Fourth-form information technology (IT) students at Cornwall College in Montego Bay look on while president of Teen for Technology, Anders Jones (right), types on one of the newest additions to the school's computer laboratory. Teens for Technology, a non- profit organisation run by teens in the United States, donated 30 reconstructed computers to the Conrwall IT Department. -File

Joanna George-Johnson teaches at Ardenne High School.