Where Centrioles Are Found
Composition
- Most centrioles are made up of nine sets of microtubule triplets, with the exception of some species, such as crabs which have nine sets of microtubule doublets. There are a few other species that deviate from the standard centriole structure. Microtubules are composed of a single type of globular protein called tubulin.
Two Main Functions
- During mitosis or cell division, the centrosome and centrioles replicate and migrate to opposite ends of the cell. Centrioles help to arrange the microtubules that move chromosomesduring cell division to ensure each daughter cell receives the appropriate number of chromosomes. Centrioles are also important for the formation of cell structures known...
Important Role in Cell Division
- Centrioles are located outside of, but near the cell nucleus. In cell division, there are several phases: in order of occurrence they are interphase, prophase, metaphase, anaphase, and telophase. Centrioles have a very important role to play in all phases of cell division. The end goal is in moving replicated chromosomes into a newly created cell.
Interphase and Replication
- In the first phase of mitosis, called interphase, centrioles replicate. This is the phase immediately prior to cell division, which marks the start of mitosis and meiosis in the cell cycle.
Prophase and Asters and The Mitotic Spindle
- In prophase, each centrosome with centrioles migrates toward opposite ends of the cell. A single pair of centrioles is positioned at each cell pole. The mitotic spindle initially appears as structures called asters which surround each centriole pair. Microtubules form spindle fibersthat extend from each centrosome, thereby separating centriole pairs and elongating the cell. You can think …
Metaphase and Positioning of Polar Fibers
- In metaphase, centrioles help to position polar fibers as they extend from the centrosome and position chromosomes along the metaphase plate. In keeping with the highway analogy, this keeps the lane straight.
Anaphase and The Sister chromatids
- In anaphase, polar fibers connected to chromosomes shorten and separate the sister chromatids(replicated chromosomes). The separated chromosomes are pulled toward opposite ends of the cell by polar fibers extending from the centrosome. At this point in the highway analogy, it is as if one car on the highway has replicated a second copy and the two cars begin …
Telophase and Two Genetically Identical Daughter Cells
- In telophase, the spindle fibers disperse as the chromosomes are cordoned off into distinct new nuclei. After cytokinesis, which is the division of the cell's cytoplasm, two genetically identical daughter cellsare produced each containing one centrosome with one centriole pair. In this final phase, using the car and highway analogy, the two cars look exactly the same, but are n…
Overview
In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers (Pinophyta), flowering plants (angiosperms) and most fungi, and are only present in the male gametes of charophytes, bryophytes, seedless vascular plants, cycads, and Ginkgo. A bound pair of centrioles, surrounded by a highly o…
History
The centrosome was discovered jointly by Walther Flemming in 1875 and Edouard Van Beneden in 1876. Edouard Van Beneden made the first observation of centrosomes as composed of two orthogonal centrioles in 1883. Theodor Boveri introduced the term "centrosome" in 1888 and the term "centriole" in 1895. The basal body was named by Theodor Wilhelm Engelmann in 1880. The pattern of centriole duplication was first worked out independently by Étienne de Harven and Jose…
Role in cell division
Centrioles are involved in the organization of the mitotic spindle and in the completion of cytokinesis. Centrioles were previously thought to be required for the formation of a mitotic spindle in animal cells. However, more recent experiments have demonstrated that cells whose centrioles have been removed via laser ablation can still progress through the G1 stage of interphase before ce…
Cellular organization
Centrioles are a very important part of centrosomes, which are involved in organizing microtubules in the cytoplasm. The position of the centriole determines the position of the nucleus and plays a crucial role in the spatial arrangement of the cell.
Fertility
Sperm centrioles are important for 2 functions: (1) to form the sperm flagellum and sperm movement and (2) for the development of the embryo after fertilization. The sperm supplies the centriole that creates the centrosome and microtubule system of the zygote.
Ciliogenesis
In flagellates and ciliates, the position of the flagellum or cilium is determined by the mother centriole, which becomes the basal body. An inability of cells to use centrioles to make functional flagella and cilia has been linked to a number of genetic and developmental diseases. In particular, the inability of centrioles to properly migrate prior to ciliary assembly has recently been linked to Meckel–Gruber syndrome.
Animal development
Proper orientation of cilia via centriole positioning toward the posterior of embryonic node cells is critical for establishing left-right asymmetry, during mammalian development.
Centriole duplication
Before DNA replication, cells contain two centrioles, an older mother centriole, and a younger daughter centriole. During cell division, a new centriole grows at the proximal end of both mother and daughter centrioles. After duplication, the two centriole pairs (the freshly assembled centriole is now a daughter centriole in each pair) will remain attached to each other orthogonally until mitosis. At that point the mother and daughter centrioles separate dependently on an enzyme c…