Centrioles, Basal bodies, Cilia, and Flagella
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Centrioles, basal bodies and flagella all have the same basic structure. Centrioles are composed of a series of nine paired tubes arranged in a circular fasion. Each of the tubes in turn is composed of a series of proteins, most important structurally being the protein tubulin. Tubulin is a complex protein and more information about tubulin and its organization into microtubules is here. Centrioles typically occur in pairs at right angles in the cytoplasm. In older texts these paired centrioles are often called the central bodies. During mitosis and meiosis in animal cells the centrioles replicate and seem to be an organizing center for various contractile proteins involved in moving the chromosomes around.
A basal body is like a centriole except that it is found at the base of a cilium or flagellum. Both centrioles and basal bodies are similar in that they consist of an outer ring of nine paired tubulin tubes
Cilia and flagella have a similar structure except that in the center of the ring of tubulin tubes is an additional pair of tubulin tubes. This arrangement is universal among all eukaryotes, such as protists, that have cilia and flagella. Cilia and flagella move in a whip like fashion which is accomplished using a seperate set of proteins that form arms atttached to the tubulin. These protein arms allow neighboring t tubulin tubes to slide past each other and bend the cilium. Cilia and flagella are similar but cilia tend to be much shorter than the length of the cell. Also cilia have a power stroke much like swimmer would have while flagella tend to pull the organism through water, as a propeller pulls an airplane throught the air.
Since eukaryote flagella and cilia move using kinetic energy generated within the structure some scientists have proposed the term undulapodia for these structures to distinguish them clearly from bacterial flagella.
pgd 6/26/99 revised 06/17/02