Prokaryotes

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Prokaryotes are organisms defined by their lack of membrane bound organelles. The origin of the word prokaryote comes from the Greek "pro", meaning before, and "karyon" which means nucleus or "kernel".  Prokaryotes lack a nucleus to store DNA. Their DNA is instead found in a circular form within the cytoplasm. The DNA in prokaryotes is naked DNA. Prokaryotes have cell walls which are a network of fibres that provides the cell with strength and rigidity. This network in the cell wall allows the cell to be freely permeable. These differ from eukaryotes which have a nucleus containing genetic information (DNA). Most prokaryotes are unicellular (single cells) but there are some that have life cycles with multi cellular stages. Bacteria (such as Escherichia coli), archaea and cynobacteria are prokaryotes[1]. The prokaryotes typically have an average cell diameter ranging between 0.5-5µm. The prokaryotes have slightly smaller ribosomes, 70S ( about 18nm diameter) as compared to eukaryotes, 80S (about 22nm diameter). No endoplasmic reticulum , mitochondria and chloroplasts are present in a prokaryote cell. Prokaryote cells moves with the help of flagella or cilia made of flagellin. Prokaryotes breed through asexual reproduction, usually either by budding or binary fission (simple division) [2]. Most prokaryote cells are small and simple in their outward appearance which are typically spherical or rod-shaped[3].


References

  1. Alberts B., Johnson A., Lewis J., Raff M., Roberts K., Walter P., (2008), Molecular Biology of The Cell, Fifth Edition, New York: Garland Science,Taylor and Francis Group, p14.
  2. Jones M., Fosbery R., Taylor D., Gregory J., (2008), Biology, Second Edition, Oxford: Cambridge University Press, p17-18.
  3. Alberts B., Johnson A., Lewis J., Raff M., Roberts K., Walter P., (2008), Molecular Biology of The Cell, Fifth Edition, New York: Garland Science,Taylor and Francis Group, p14.
[1]
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