How cells multiply

While we are growing and developing into adults our cells need to multiply. The nucleus in a cell sends out messages to organise this.

Our cells are amazing. They really can multiply in number as one cell splits into two cells, these two cells both split to become four cells, four cells become eight, eight cells become sixteen............and so on. It’s easy to see how this could get out of hand! So this process must be carefully controlled.

Once we become adults only some cells retain the ability to multiply, for example when our bodies need to heal after an injury or an operation.

And cells only multiply at certain times.

• Nerve cells (shown in the photograph) never multiply.
• Liver cells multiply every one or two years.
• Cells lining the stomach multiply at least twice a day!

Cell growth and multiplication is part of a continual process called the cell cycle. To move through the different stages of the cell cycle each cell has to go through a series of checkpoints. These checkpoints act a bit like traffic lights and they only give the green light to a cell that is ready to go through to the next stage in the cycle. Only healthy cells are allowed to multiply and so the cell cycle must control which cells are allowed through. Damaged cells are stopped and either repaired or destroyed.

Mitosis

The cell cycle is made up of four linked series of events and one of these events is called mitosis.

During mitosis the DNA is copied and shared out equally. This means that all the chromosomes must be duplicated and separated into two full sets, one at each end of the cell that is splitting in two. The other material that makes up the cell also splits in two. The result is two identical daughter cells. The photographs below show one cell mulitplying into two cells during mitosis.

The 4 main stages of mitosis are:

1. Prophase - when the genetic material in the cell, which is normally loosely bundled, condenses to form chromosomes. Each chromosome has duplicated and now consists of two sister chromatids
2. Metaphase - when the chromosomes align themselves along the cell spindle in the middle of the cell, ready to separate
3. Anaphase - when the sister chromatids separate and move to opposite ends of the cell
4. Telophase - when the cell prepares to cleave in two

All images were kindly provided by the EM Unit at the London Research Institute and the Science Photo Library.