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Flagella are long protrusions on the back of a cell such as the tail of the sperm cell. They can propel a cell through liquid or fluid mediums via their undulation and fluctuation. Eukaryotic flagella are elongated versions of cilia whereas bacterial flagella are completely different both in structure and mechansims[1].

Bacterial flagella are made entirely of protein and have a diameter of around 12-30nm. Several thousand protein subunit molecules of Flagellin make up one bacterial flagellum, of these molecules there are two types. Three types of flagella arrangement are understood to occur: monotrichous, peritrichous and lophotrichous. Monotrichous flagellum are single and Polar, a peritrichous arrangement occurs with flagella over the entire cell surface, whilst lophotrichous arrangements occur when there are many polar flagella[2].


  1. Albert, B. et al. (2008) Molecular Biology of the Cell. New York: Garland Publishing
  2. Brooks et al: Jawetz, Melnick and Adelberg's Medical Microbiology, 24th edition, The McGraw-Hill Compaines, Inc, 2007
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