How does Cell Division Work
There’s an old joke that goes, ‘Let’s make like an amoeba and split’. Every organism goes through cell division, although in the case of the humble amoeba, cell division means creating another amoeba. Amoebas are a type of cell known as a prokaryote (which also includes things like bacteria).
It doesn’t have a nucleus, but has its DNA and other genetic material floating around inside the cell. It reproduces asexually through binary fission or a process called budding.
On the other hand, us humans – and every other multi-celled organism in existence – are quite a bit more complicated. As eukaryotes, our cells undergo two different types of cell division depending on the type of cell: meiosis and mitosis. Both are complex, multi-step processes that happen very quickly. In order to sexually reproduce, our bodies create special sex cells called gametes (in animals we call these sperm in males, and eggs in females).
Gametes are haploid cells because they contain 23 chromosomes, which are considered a single set. During reproduction, they merge to form a cell containing 46 chromosomes, called a diploid. But first, meiosis splits the original diploid cells, with the chromosomes duplicating, shuffling and reforming into four unique haploid cells.
In contrast, mitosis produces two identical haploid cells. It’s a different process from the prokaryotic asexual reproduction, but in humans and other multi-celled organisms it’s a sort of maintenance programme. Your body is undergoing mitosis constantly as all sorts of cells die and are replaced. Each human has between 50 and 75 trillion different cells and about 200 different types of cell.
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Tumours
Tumours can be malignant (cancerous) or non-malignant, and at their most basic are the result of abnormal cell growth. The nucleus of every cell contains material that tells the cell when it’s time to grow and divide (mitosis). There’s a strict balance so that the new healthy cells are always replacing old, dying or damaged cells. Sometimes, however, cells get the message to grow and divide more often than they’re supposed to, throwing off the equilibrium. Typically this comes from a genetic mutation – that is, there’s a problem with the programming. These genetic mutations can be caused by anything from environmental factors to viruses. In cancerous tumours, the cells don’t die like normal cells – instead, the mutation allows them to replicate indefinitely.
How does Mitosis work
1. Interphase – The cell grows and strands of DNA within the cell nucleus replicate and divide into two.
2. Prophase – The 96 chromosomes consolidate into visible X-shaped structures called chromatids. The cell’s nucleus begins to breakdown.
3. Metaphase – Structures called centrioles form spindle fibres that move to each side of the cell, and the chromatids line up along an imaginary dividing line.
4. Anaphase – The spindle fibres pull the chromatids towards opposite sides as the cell begins to split.
5. Telophase – Nuclear membranes form around the sets of chromatids (now called chromosomes). In the final phase-cytokinesis – the rest of the cell divides.
How does Meiosis work
1. Parent cell – Meiosis starts the same way as mitosis – with a diploid cell containing 46 chromosomes. The DNA strands replicate and divide.
2. Prophase – The chromosomes match up with their corresponding strand. Enzymes remove pieces of DNA from each and genes swap between the chromosomes before re-pairing.
3. Metaphase – At this point, unlike in mitosis, chromosome pairs line up on either side of an imaginary line in the cell.
4. Anaphase – Next, the chromosome pairs separate, with half moving to one side and half moving to the other.
5. Telophase – Nuclei start to form around each chromosome as the cell divides into two daughter cells, each with 46 chromosomes.
6. Daughter cells – The two daughter cells go through the entire process again, ultimately forming four daughter cells, each with 23 chromosomes.
Read What happens when cell division goes wrong?