centriole

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centriole:

see mitosismitosis
, process of nuclear division in a living cell by which the carriers of hereditary information, or the chromosomes, are exactly replicated and the two copies distributed to identical daughter nuclei.
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Centriole

A morphologically complex cellular organelle at the focus of centrosomes in animal cells and some lower plant cells. Prokaryotes, some lower animal cells, higher plant cells, and a few exceptional higher animal cells do not have centrioles in their centrosomes. Centrioles typically are not found singly; the centrosome of higher animal cells contains a pair of centrioles (together called the diplosome), arranged at right angles to each other and separated by a distance ranging from 250 nanometers to several micrometers. See Centrosome

Centrioles are typically 300–700 nm in length and 250 nm in diameter. Although they can be detected by the light microscope, an electron microscope is required to resolve their substructure. At the electron microscopic level, a centriole consists of a hollow cylinder of nine triplet microtubules in a pinwheel arrangement (see illustration). Within each triplet, one microtubule (the A tubule) is a complete microtubule, while the others (the B and C tubules) share a portion of their wall with the adjacent tubule. In some cells these nine triplet microtubules are embedded in a densely staining cylindrical matrix that is spatially distinct from the pericentriolar material of the centrosome. Structures found in the lumen or core of the centriole include linkers between the triplets, granules, fibers, a cartwheel structure at one end of the centriole, and sometimes a small vesicle.

Diagrams of centriole showing ( a ) arrangement of microtubules and ( b ) cross section of proximal end, with nine triplet microtubules (A, B, and C) and central cartwheel structureenlarge picture
Diagrams of centriole showing (a) arrangement of microtubules and (b) cross section of proximal end, with nine triplet microtubules (A, B, and C) and central cartwheel structure

Centrioles have a close structural similarity to basal bodies, which organize the axoneme of cilia and flagella. In many types of mammalian somatic cells, the older of the two centrioles in the centrosome can act as a basal body during the interphase portion of the cell cycle. In such cases, tapered projections, called basal feet, are often observed on the external surface of the centriole that is acting as the basal body. Microtubules are attached to the globular tips of the basal feet and may serve to anchor this centriole in the cell.

During interphase the centrosome nucleates the array of cytoplasmic microtubules; later in the cell cycle the centrosome duplicates, and the daughter centrosomes form the poles of the mitotic (or meiotic) spindle. The terms “centriole” and “centrosome” are sometimes erroneously used interchangeably; centrioles are not the centrosome itself, but a part of it. The centrosome of higher animal cells has at its center a pair of centrioles, arranged at right angles to each other and separated by 250 nm or less.

The only clearly demonstrated role for the centriole is to organize the axoneme (central microtubular complex) of the primary cilium in cells having this structure, and the flagellar axoneme in sperm cells. Other possible functions for centrioles are a matter of debate. Some authorities assert that when present in the centrosome, centrioles contain activities that serve to organize the centrosome, determine the number of centrosomes in a cell, and control the doubling of the centrosome as a whole before mitosis. Others believe that centrioles have no role in the formation and doubling of the centrosomes but are associated with the centrosomes only to ensure the equal distribution of basal bodies during cell division. See Cell (biology)

Centriole

 

a permanent structure in all animal cells and some plant cells; the main part of the mitotic center. The centrioles are surrounded by the centrosome. They are cylindrical and measure 0.2–0.8 micrometers in length. The wall of a centriole consists of nine groups of microtubules. Nondividing cells have two adjacent centrioles. During cell division the centrioles separate and migrate to opposite poles, thereby determining the axis of the spindle. In the absence of centrioles, their function is performed by membrane elements collected at the poles of the cell.

centriole

[′sen·trē‚ōl]
(cell and molecular biology)
A complex cellular organelle forming the center of the centrosome in most cells; usually found near the nucleus in interphase cells and at the spindle poles during mitosis.
References in periodicals archive ?
Distinct mechanisms eliminate mother and daughter centrioles in meiosis of starfish oocytes.
Unlike animal cells, where microtubules are nucleated at discrete centriole containing centrosomes, plant cells produced a bewildering assortment of microtubule arrays in the absence of centrosomes.
Early spermatids also have two centrioles arranged at 90 degrees to each other, with an axoneme originating from the centriole closest to the plasma membrane (Fig.
Centriole duplication in lysates of Spisula solidissima oocytes.
Centrin-2 is required for centriole duplication in mammalian cells.
Centrioles have been traced in all stages of pre-implantation embryogenesis and also in embryonic stem cells and the sperm centriole is undoubtedly the precursor of centrioles in all foetal and adult somatic cells (2,6).
Throughout early prophase, the centrioles migrate laterally and eventually occupy opposite sides of the cell.
The chromosomes are attached to the spindle fibers and anchored by the centrioles.
Homologous Chromosomes--Pairs of chromosomes that are the same length, that have their centrioles in the same position, and that pair up during synapsis in meiosis.
Centrioles are critical for the proper execution of important biological processes ranging from cell division to cell signaling.
While this is occurring, the two centrioles migrate to the side of the nucleus opposite to that which is being covered by the acrosomal vesicle.
5) In human spermatogenesis characteristic double centrioles are seen.