In the last article we looked at mitosis as a method of cell division. However, mitosis can only take place in eukaryotic cells. Prokaryotic cells such as bacteria, which don’t have a nucleus, divide by binary fission. This process produces two genetically identical daughter cells from the parent cell, and is a method of asexual reproduction.
Binary fission – the process
- All the DNA in the cell replicates. The circular DNA (the only chromosome in the cell) is replicated once to give two copies. Plasmids (small circles of DNA) can be replicated many times.
- The cell elongates and the circular DNA moves to the opposite poles of the cell.
- The cytoplasm divides, the cell membrane grows inwards, and a new cell wall forms between the two daughter cells. Each daughter cell will have one copy of the circular DNA, but can have variable numbers of plasmids.
This process can take as little as 20 minutes, so bacteria can reproduce extremely quickly until something becomes limiting e.g. oxygen or nutrients.
Interestingly, mitochondria and chloroplasts also replicate themselves using binary fission. They contain their own DNA from way back in evolution, so must replicate their DNA to divide.
A note on viruses
Remember that viruses are acellular – they are not cells. They are not able to replicate themselves without using a host cell, so do not undergo binary fission or mitosis. You will learn about how viruses replicate themselves inside a host cell in the immune system topic.
Summary
It barely seems worth summarising such a short article! There isn’t a lot to learn here, just be aware of the differences and similarities between mitosis and binary fission. Both produce two genetically identical daughter cells, but the number of plasmids can vary in binary fission. Mitosis requires a nucleus and centrioles, so only happens in eukaryotic cells.
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