Centriol is the intracellular organelle of a eukaryotic cell. The centriole size is on the border of the resolution of the light microscope.
These organelles in dividing cells take part in the formation of the spindle of division and are located at its poles. In non-dividing cells (e.g. epithelium ), centrioles often determine the polarity of the cells and are located near the Golgi complex .
Content
Building
The term was proposed by Theodore Boveri in 1895 . The fine structure of centrioles was studied using an electron microscope. In some objects, it was possible to observe centrioles, usually located in a pair (diplosome), and surrounded by a zone of lighter cytoplasm, from which thin fibrils radially radiate (centrosphere). The combination of centrioles and centrospheres is called the cell center .
Most often, a pair of centrioles lies near the core . Each centriole is built of 27 cylindrical elements ( tubulin microtubules ), grouped into 9 triplets. These triplets are located around a circle, forming a hollow cylinder. Its length is 0.3–0.5 μm (equal to the length of each triplet), and its diameter is about 0.15 μm. In each triplet, the first microtubule (A microtubule) has a diameter of about 25 nm, a wall thickness of 5 nm, and consists of 13 protofilaments. The second and third microtubules (B and C) differ from A-microtubules in that they are incomplete, contain 11 protofilaments and are adjacent to their neighbors. Each triplet is located to the radius of such a cylinder at an angle of about 40 °.
Functions
Centrioles are always located in a material that does not have a clearly defined structure that initiates the development of microtubules. This area of the cell is called the centrosome . It is she who forms the spindle of division, and not centrioli. This allows us to explain the fact why plants and fungi that do not have centrioles are able to form a spindle. The function of centrioles remains unknown. Perhaps they participate in the orientation of the spindle according to the poles to which cell division will occur ( cytokinesis ). Modified centrioles are also located at the base of flagella and cilia in protozoa, where they are called basal bodies .
Development Cycle
Usually, during the cell cycle, centriole doubles once. Next to each half of the "mother" centriole, a "daughter" cylinder is being completed; this occurs, as a rule, during the G2 period of interphase . In prophase of mitosis, two centrioles diverge to the poles of the cell and form two centrosomes . Centrosomes, in turn, serve as CTOMs ( microtubule organization centers ) of the spindle. However, there are many deviations from this general scheme. In many cells, centrioles repeatedly double in a single cell cycle. When the eggs mature in the vast majority of animals, centrioles break down (many of the proteins that make up the centrosomes are still present in the cell). With the formation of sperm , on the contrary, the centrosome degrades; one of the centrioles turns into the basal body of the flagellum, and the second remains intact. However, in the mouse and other rodents (unlike the rest of the mammals studied), as well as in snails, both sperm centrioles degrade. After fertilization, new centrioles arise in the zygote, either due to the doubling of the centriole introduced by the sperm, or due to the formation again [1] .
Notes
- ↑ Manandhar, G., Schatten, H., Sutovsky, P. (2005). Centrosome reduction during gametogenesis and its significance. Biology of reproduction 72 : 2–13. DOI : 10.1095 / biolreprod.104.031245
Literature
Yu. S. Chentsov, General cytology. M., Moscow Publishing House. 1978