Centrioles and Centrosomes

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Centrioles are built from a cylindrical array of 9 microtubules, each of which has attached to it 2 partial microtubules.

The photo (courtesy of E. deHarven) is an electron micrograph showing a cross section of a centriole with its array of nine triplets of microtubules. The magnification is approximately 305,000.

When a cell enters the cell cycle and passes through S phase, each centriole is duplicated. A "daughter" centriole grows out of the side of each parent ("mother") centriole. Thus centriole replication — like DNA replication (which is occurring at the same time) — is semiconservative.

Centrioles are a key feature of eukaryotic cells and presumably arose with the first eukaryotes. A few groups have since lost their centrioles:

Functions of centrioles.

Link to a page describing cilia, flagella, and the primary cilium.

The Centrosome

The centrosome

The photo (courtesy of Tim Mitchison) shows microtubules growing in vitro from an isolated centrosome. The centrosome was supplied with a mixture of alpha and beta tubulin monomers. These spontaneously assembled into microtubules only in the presence of centrosomes.

Spindle fibers have three destinations:

All three groups of spindle fibers participate in

Other Functions of Centrosomes

In addition to their role in spindle formation, centrosomes play other important roles in animal cells:

Centrosomes and Cancer

Cancer cells often have more than the normal number of centrosomes. They also are aneuploid (have abnormal numbers of chromosomes), and considering the role of centrosomes in chromosome movement, it is tempting to think that the two phenomena are related.

Mutations in the tumor suppressor gene p53 seem to predispose the cell to excess replication of the centrosomes.

Chromosome movement in mitosis also involves polymerization and depolymerization of microtubules.

Because the hallmark of cancer cells is uncontrolled mitosis, both vincristine and Taxol are used as anticancer drugs

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15 June 2015