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Download Lec. No.10 Centrosome In cell biology, the centrosome is an
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Lec. No.10 Centrosome In cell biology, the centrosome is an organelle that serves as the main microtubules organizing center ( MTOC) of the animal cell ,it is duplicated during S phase of the cell cycle . Centerioles , found only in animal cells, these paired organelles are located together near the nucleus. Each centerioles is made of nine bundles of microtubules (three per bundle) arranged in a ring. Just before mitosis, the two centrosomes move part until they are on opposite side of the nucleus and organized into a spindle-shaped formation that called spindle fibers.These spindle fibers act as indicator for the alignment of the chromosomes as they separate later during the process of cell division. Functions of centrioles. In nondividing cells, the mother centriole can attach to the inner side of the plasma membrane forming a basal body. In almost all types of cell, the basal body forms a nonmotile primary cilium. In cells with a flagellum, e.g. sperm, the flagellum develops from a single basal body. (While sperm cells have a basal body, eggs have none. So the sperm's basal body is absolutely essential for forming a centrosome which will form a spindle enabling the first division of the zygote to take place. In ciliated cells such as o the columnar epithelial cells of the lungs o ciliated protozoans like the paramecium 6 Centrosomes Cilia & Flagella Eukaryotic cilia and flagella are hair‐like cellular appendages composed of specialized microtubules and covered by a specialized extension of the cellular membrane, found in most microorganisms and animals, cilia function to move a cell or to help transport fluid or materials past them. The respiratory tract in humans is lined with cilia that keep inhaled dust, and harmful microorganisms from entering the lungs. Cilia are usually shorter and occur together in much greater numbers than flagella. In eukaryotic cells, cilia and flagella contain the motor protein (dynein) and (microtubles), the core of each of the structures is termed the (axoneme) and contains two central microtubules that are surrounded by an outer ring of nine doublet microtubules. Dynein molecules are located around the axoneme. A plasma membrane surrounds the entire axoneme complex, which is attached to the cell at a structure termed the basal body. 7 Basal Body: Basal bodies are modified centrioles that give rise to cilia and flagella. Basal body (also known as a kinetosome). Basal bodies maintain the basic outer ring structure of the axoneme of the cilia and The basal body is structurally identical to the centrioles. Inclusions bodies Inclusion bodies, sometimes called elementary bodies, are nuclear or cytoplasmic aggregates of stainable substances, usually proteins. Inclusion bodies can also be hallmarks of genetic diseases, as in the case of Neuronal Inclusion bodies in disorders like frontotemporal dementia and Parkinson's disease. Inclusions bodies: are considered to be nonliving components of the cell that neither possess metabolic activity nor are bounded by membranes. The most common inclusions are glycogen, lipid droplet, pigments, and crystals. 1-Glycogen: is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals and fungi. The olysaccharide structure represents the main storage form of glucose in the body. In humans, glycogen is made and stored primarily in the 8 cells of the liver and the muscles, hydrated with three or four parts of water. Glycogen functions as the secondary longterm energy storage, with the primary energy stores being fats held in adipose tissue. Muscle glycogen is converted into glucose by muscle cells, and liver glycogen converts to glucose for use throughout the body. 2-Lipids: is a storage forms of triglycerides, are stored in specialized cells, adipocytes, also located as individual droplets in various cell types. Especially those of the liver, lipids are source of energy. 3- Pigments: there are deposits of colored substances include: A- Melanin: the most common pigment in the body, its dark brown pigment present in the skin, hair, retina, and some parts of the central nervous system (C.N.S). Melanin is produced by the oxidation of the amino acid tyrosine, in a specialized group of cells known as melanocytes. B-Lipofuscin: its yellow to brown pigment found in long lived cells, like neurons of the C.N.S and cardiac muscles. Lipofuscin pigments are membrane-bound and represent the indigestible remnants of lysosomal activity. C- Hemosiderin: it’s a gold-yellow pigment. It’s the end product of Hb degradation of old red blood cells. They are present in the liver, spleen and bone marrow. D- Crystals: Crystals are structures of crystalline forms of certain proteins . They are not commonly found in cells, with the exception of steroid cells, and interstitial cells of testes, and occasionally in macrophages. 9 Ultrastructure of basal body Ultrastructure of basal body Ultrastructure of basal body 10