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Membrane cellular organelles
Last reviewed: 23.04.2024
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Non-membrane organelles of the cell include centrioles, microtubules, filaments, ribosomes and polysomes.
Centrioles (centrioli), usually two (diplosome), are small bodies surrounded by a dense site of the cytoplasm. From each centriole ray-shaped microtubules departing, called centrospheres. The diplosome (two centrioles) and the centrosphere form a cell center, which is located either near the cell nucleus, or near the surface of the Golgi complex. Centrioles in the Diplomat are at an angle to each other. Each centriole is a cylinder whose wall consists of microtubules about 0.5 μm in length and about 0.25 μm in diameter.
Centrioles are semi-autonomous self-renewing structures that double when dividing the cell. In the beginning, the centrioles diverge to the sides, and near each of them a daughter centriole is formed. Thus, before division in a cell there are two pairwise connected centrioles - two diplosomes.
Microtubules (microtubuli) are of different length hollow cylinders with a diameter of 20-30 nm. Many microtubules are part of the centrosphere, where they have a radial direction. Other microtubules are located under the cytolemma, in the apical part of the cell. Here, together with the bundles of microfilaments, they form an intracellular three-dimensional network. The walls of microtubules have a thickness of 6-8 nm. Microtubules form the cytoskeleton of the cell and participate in the transport of substances inside it.
The cytoskeleton of the cell is a three-dimensional network in which the various protein filaments are interconnected by transverse bridges. In the formation of the cytoskeleton, in addition to microtubules, actin, myosin and intermediate filaments also take part, which perform not only the supporting, but also the motor function of the cell.
Ribosomes (ribosomae) are present in all cells, they participate in the formation of protein molecules - in protein synthesis. The size of the ribosome is 20x30 nm. These are complex ribonucleoproteins consisting of proteins and RNA molecules in a 1: 1 ratio. Distinguish ribosomes single - mono-ribosomes and assembled into groups - polyribosomes, or polysomes. Ribosomes are located freely on the membrane surface, resulting in the formation of a granular (granular) endoplasmic reticulum.
Inclusions (cellular granules) are formed as a result of the vital activity of cells. Their appearance depends on the nature of the metabolic processes in the cell. There are trophic inclusions: fatty, proteinaceous, which can accumulate in the hyaloplasm as reserve materials necessary for the vital activity of the cell. The same inclusions include polysaccharides that are in cells in the form of glycogen. Secretory inclusions containing biologically active substances accumulate in glandular cells. Inclusions can be pigmented, trapped in the body (into cells) from the outside (dyes, dust particles) or formed in the body as a result of its vital activity (hemoglobin, melanin, lipofuscin, etc.).
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