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Non-membrane organelles of the cell
Last reviewed: 06.07.2025
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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 area of cytoplasm. Microtubules called centrospheres extend radially from each centriole. Diplosome (two centrioles) and centrosphere form the cell center, which is located either near the cell nucleus or near the surface of the Golgi complex. Centrioles in the diplosome are located at an angle to each other. Each centriole is a cylinder, the wall of which consists of microtubules about 0.5 μm long and about 0.25 μm in diameter.
Centrioles are semi-autonomous self-renewing structures that double during cell division. Initially, the centrioles diverge to the sides, and a daughter centriole is formed near each of them. Thus, before division, the cell has two paired centrioles - two diplosomes.
Microtubules (microtubuli) are hollow cylinders of varying lengths 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 bundles of microfilaments, they form an intracellular three-dimensional network. The walls of the microtubules are 6-8 nm thick. Microtubules form the cytoskeleton of the cell and participate in the transport of substances within it.
The cell cytoskeleton is a three-dimensional network in which various protein filaments are linked together by cross-bridges. In addition to microtubules, actin, myosin, and intermediate filaments also participate in the formation of the cytoskeleton, 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 a ribosome is 20x30 nm. These are complex ribonucleoproteins consisting of proteins and RNA molecules in a 1:1 ratio. There are single ribosomes - monoribosomes and those collected in groups - polyribosomes, or polysomes. Ribosomes are located freely on the surface of membranes, as a result of which a granular endoplasmic reticulum is formed.
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. Trophic inclusions are distinguished: fat, protein, which can accumulate in the hyaloplasm as reserve materials necessary for the vital activity of the cell. These inclusions also include polysaccharides found in cells in the form of glycogen. Secretory inclusions containing biologically active substances accumulate in glandular cells. Inclusions can be pigmented, entering the body (cells) from the outside (dyes, dust particles) or formed in the body itself as a result of its vital activity (hemoglobin, melanin, lipofuscin, etc.).
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