All cell organelles are not membrane bound like mitochondria, plastics etc. Some of them play a structural role more than a functional role in the cytoplasm. Few provide shape and support, whereas some provide mobility while helps in reproduction. Let us study about this class of organelles briefly.
It is a continuous network of filamentous proteinaceous structures that run throughout the cytoplasm, from the nucleus to the plasma membrane. It is found in all living cells, notably in the eukaryotes. The cytoskeleton matrix is composed of different types of proteins that can divide rapidly or disassemble depending on the requirement of the cells. The primary functions include providing the shape and mechanical resistance to the cell against deformation, the contractile nature of the filaments helps in motility and during cytokinesis.
Cilia and Flagella
Cilia are hair-like projections, small structures, present outside the cell wall and work like oars to either move the cell or the extracellular fluid. Flagella are slightly bigger and are responsible for the cell movements. The eukaryotic flagellum structurally differs from its prokaryotic counterpart. The core of the cilium and flagellum is called as axoneme which contains 9 pairs of gradually arranged peripheral microtubules and a set of central microtubules running parallel to the axis. The central tubules are interconnected by a bridge and are embedded by a central sheath. One of the peripheral microtubular pairs is also interconnected to the central sheath by a radial spoke. Hence there is a total of 9 radial spokes. The cilia and flagella emerge from centriole-like structures called basal bodies.
Centrosome and Centrioles
The centrosome is an organelle made up of two mutually perpendicular structures known as centrioles. Each centriole is composed of 9 equally spaced peripheral fibrils of tubulin protein and the fibril is a set of interlinked triplets. The core part of the centriole is known as a hub and is proteinaceous in nature. The hub connects the peripheral fibrils via radial spoke which is made up of proteins. The centrioles from the basal bodies of the cilia and flagella give rise to spindle fibers during cell division.
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