Cytoplasmic Organelles II PDF

Cytoplasmic Organelles II By: Dr. Moustafa Al Sawy Dr. Shaimaa Mohamed Amer MBBCH, M.SC. M.D HISTOLOGY MBBCH, M.SC. M.D HISTOLOGY Associate Professor of Histology & Cell Biology...

Cytoplasmic Organelles II By: Dr. Moustafa Al Sawy Dr. Shaimaa Mohamed Amer MBBCH, M.SC. M.D HISTOLOGY MBBCH, M.SC. M.D HISTOLOGY Associate Professor of Histology & Cell Biology Associate Professor of Histology & Cell Biology Certified Medical Educator Intended Learning Outcomes (ILOs): Knowledge : By the end of the lecture , each student will be able to: 1.Describe LM & EM and mention functions of (lysosomes, Endoplasmic Reticulum, Peroxisomes). 2.Describe LM & EM and mention functions of non-membranous organelles.  4-Lysosomes Lys o s omes Site & Origin *Membranous rounded vesicles. *Digestive apparatus of the cell. *Numerous in phagocytic cells as macrophage, neutrophil & osteoclast. Structure *LM. Demonstrated by special histochemical methods- detection of their enzymes.  Lys o s omes Chemical composition: *Lysosomes contain hydrolytic enzymes active at acidic PH. *The limiting membrane of lysosomes to maintain the acidic environment for the function of its enzymes and to protect the reminder of the cell from the effects of the contained enzymes that can lyse the cell (autolysis)  EM = Types of Lysosomes Primary Lysosomes Secondary Lysosomes Large heterogeneous vesicles result from Newly formed from Golgi apparatus. fusion of primary lysosomes with Small homogenous vesicles. phagosomes and have different names. Functions of lysosomes (intracellular digestion): 1.Digestion of foreign bodies as bacteria = Cellular defense mechanisms 2.Digestion of old organelles = normal replacement of cellular components to maintain the cell health. 3.Digestion of the whole cell after death (rupture membrane) = postmortem autolysis. 4. Help the sperm to penetrate the ovum (fertilization). 5. In thyroid gland: breaks inactive hormone into the active form. 6. Residual bodies play important role in the aging process.  Medical Application Lysosomal storage disorders *Genetic defects in the production of specific lysosomal acid hydrolases lead to an inability to degrade specific classes of molecule, which then accumulate in the acid vesicle system. *Most of these defects are inherited as single gene autosomal recessive traits. Examples: 1.Lysosomal glycogen storage disease (acid maltase deficiency) leads to the accumulation of glycogen, which cannot be broken down. 2.Tay–Sachs disease results from a deficiency in an enzyme degrading one of the sphingolipids (hexosaminidase- A deficiency). 3.Huge amounts of lipid accumulate in lysosomes and lead to severe neuronal degeneration. 5,6- Endoplasmic Reticulum There are two types  5- Rough Endoplasmic Reticulum 6- Smooth Endoplasmic Reticulum (RER) (SER) It is a membranous organelle. It is a membranous organelle. Structure: Structure: By L.M.: *It shows localized cytoplasmic basophilia in By L.M.: some kinds of cells. Can not be seen. By E.M.: By E.M.: *It consists of a network of membranous *It consists of network of branching vesicles and flat tubules called cisternae. anastomosing tubules. *Their surfaces are covered with ribosomes. *Their surfaces have no ribosomes. rER (rough or granular ) sER (smooth or agranular)  Functions of RER: It synthesizes the proteins in the attached ribosomes & separated it from cytosol, within its cisternae. 1. Formation of secretory proteins that export outside 2. Formation of lysosomal enzymes. 3. Formation of plasma membrane proteins.  Functions of sER (differ according to the cell) 1- In steroid secreting cells e.g cells of adrenal cortex: synthesis of steroid hormones. 2- In liver cells: - Responsible for detoxification of certain drugs. - Contains enzymes which is involved in the utilization of glucose originating from glycogen. N.B: physiological jaundice in newborn is caused by immaturity of sER of liver cells that unable to conjugate the bile. 3- Synthesis of phospholipids for all cell membranes. 4- Columnar absorptive cells of small intestine: Lipid synthesis. 5- In skeletal and cardiac muscle it regulates the calcium level essential for muscular contraction. 6-In parietal cells of the stomach, the it is responsible for concentration of Cl- in order to form HCI. Proteasomes Structure. Non membranous organelles made of four stacked rings, each composed of seven proteins including proteases. At each end of the cylinder is a regulatory particle that contains ATPase and recognizes proteins Alzheimer’s disease and attached to ubiquitin. Huntington’s disease are two Function. neurologic disorders caused 2. Removal and restrict the activity of by accumulation of protein nonfunctional proteins. inside the cells due to failure N.B. Ubiquitin is a cytoplasmic protein that of degradation by attached to the non functional proteins. proteasomes. August 25, 2024  7- Peroxisomes (Microbodies) Structure: Membranous organelles contain oxidative enzymes. Similar to lysosomes but larger. LM: not demonstrated EM: finely granular homogeneous contents but less dense than lysosomes. Functions: 1.Beta oxidation of long chain fatty acids producing H2O2 which detoxified noxious agents & kill microorganisms. 2.Reduce excess H2O2 by catalase enzymes to O2 and H2O. 3.Lipid metabolism. 4. These are abundant in liver and kidney cells.  Medical Application *A large number of disorders arise from defective peroxisomal proteins, because this organelle is involved in several metabolic pathways. *Probably the most common peroxisomal disorder is X-chromosome-linked adrenoleukodystrophy, caused by a defective integral membrane protein that participates in transporting very long-chain fatty acids into the peroxisome for Beta oxidation. *Accumulation of these fatty acids in body fluids destroys the myelin sheaths in nerve tissue, causing severe neurologic symptoms.  Ribosomes Small, rounded or oval cytoplasmic organelles. Solitary Free Polysomes RIBOSOMES held by mRNA Attached Forming rER  Ribosomes Free Ribosomes Attached Ribosomes Freely distributed in the cytoplasm & Attached to membranes of endoplasmic Site mitochondrial matrix. reticulum (ER) & outer nuclear membrane. Structure LM (Minute basophilic granules.) Diffuse cytoplasmic basophilia. Localized cytoplasmic basophilia. as Nissl granules of nerve cells Ribosomes are formed of 2 subunits, a large and a small one. EM Origin & Ch. C. (M. B.) Formed in nucleolus (RNA & protein. Ribonucleoprotein). Functions Synthesis of protein for cell growth & Synthesis of protein for secretory activity & regeneration. formation of secretory granules.  Cytoskeleton Made of proteins. *Structural framework of the cell. *Maintains cell shape, stabilizes cell attachments & plays a role in motility. *Includes microtubules, microfilaments  Microtubules Microfilaments Site All cells either singly or in groups. Most Cells either singly or in groups. Difficult to be seen by LM, appear as Difficult to be seen by LM. Structure LM filaments. Long slender, tubules. Threads like structures EM Thick filaments of myosin (muscle cells). Circles in cross sections. Thin filaments of actin (muscle cells). Intermediate filaments include 5 types: 1-Keratin (tonofilaments) in epithelial cells. 2-Vimentin filaments in fibroblasts & mesenchymal cells. 3-Desmin filaments in all forms of muscles. 4-Neurofilaments in nerve cells. 5-Glial filaments in neuroglial cells of CNS. 1.Skeleton of the cell 1.Muscle contraction. Functions (cytoskeleton). 2-Movements of cytoplasm. 3-Amoeboid movements of leucocytes. 2.Preserve the cell shape. 4-Movements of microvilli. 5-Separation of cytoplasm (cell division). 3-Motility of cilia & flagella. 4-Form spindle, during cell division. 5-Transport substances within cytoplasm.  Medical Application Several inhibitory compounds used by cell biologists to study details of microtubule dynamics are also widely used in cancer chemotherapy to block activity of the mitotic spindle in rapidly growing neoplastic cells. Such drugs include vinblastine, vincristine, and paclitaxel, all of which were originally discovered as plant derivatives. The presence of a specific type of intermediate filament in tumors can often reveal the cellular origin of the tumor, information important for diagnosis and treatment of the cancer. Identification of intermediate filament proteins by means of immunocytochemical methods is a routine procedure. One example is the use of GFAP to identify astrocytomas, the most common type of brain tumor.  Centrioles -The centrosome is a non-membranous organelle - Found only in cells capable of mitosis near the nucleus. - Between nucleus & free surface of cell or between nucleus & Golgi Complex. Mature muscle and nerve cells lack a centrosome. L/M: Two centrioles appear as small bodies. They are surrounded with pale area of cytoplasm (centrosome matrix) forming centrosome. E/M:2 cylinders, perpendicular to each other. The wall of each centriole is made of nine peripheral bundles of microtubules. Each bundle is made of three fused microtubules (triplets) ( 27microtubules). - Made of protein of microtubules. Functions: 1-Initiation of cell division & spindle formation. 2-Act as an organizing center for polymerization of microtubules MTOC. 3-Formation of cilia & flagella.  Cilia and Flagella - They contains cytoplasm & microtubules bounded by cell membrane. - LM: Cilia are motile hair- like projections arising from the free surface of certain epithelial cells (lining epithelium of upper respiratory. - Flagellum is single process with 100-200 um in length (much longer than cilia) in the tail of spermatozoon.  Cilia Motile hair like processes. Site: Free surfaces of some epithelial cells respiratory tract. Structure: * LM : Single or in large numbers. * EM :Covered by a plasmalemma. Axoneme (shaft), basal body & rootlet. Axoneme : 20 microtubules. Nine peripheral pairs of fused microtubules (doublets).  Cilia Central pair of individual microtubules (9+2). Radial projections (spokes) extend from the doublets to central pair of microtubules. Basal Body: has the same structure as the centriole. The wall consists of nine triplet microtubules (9+0). Rootlet: are anchoring microtubules from basal body to cytoplasm to fix the cilia. Functions: Beat in one direction to help movement of particles or fluids from place to another.  Flagella Site :Tails of sperms. Structure: Similar to cilia, in structure but longer and larger.  Medical Application *Several mutations have been described in the proteins of the cilia & flagella. They are responsible for the Kartagener or immotile cilia syndrome. *The symptoms are immotile spermatozoa, male infertility, & chronic respiratory infections caused by the lack of the cleansing action of cilia in the respiratory tract. Case Scenario A sample of adrenal cortex obtained at autopsy is fixed with formalin, embedded in paraffin, sectioned at 6 μm, stained with H&E, and examined by light microscopy. Cells of the zona fasciculata appear washed out and “spongy” due to an accumulation of cholesterol and other precursors for steroid hormone biosynthesis. Electron microscopic examination of these “steroid factory” cells would be expected to show an abundance of which of the following organelles? (A) Autophagic vacuoles (B) Dense-core secretory granules (C) Golgi apparatus (D) Rough endoplasmic reticulum (E) Smooth endoplasmic reticulum Any Questions?  References: 1.Basic Histology: Text & Atlas. Editor: Luiz Carlos Junqueira, MD, PhD; Jose Carneiro, MD, PhD. 14th Ed, chapter 2. 2. Wheatear’s functional histology. A text & color atlas.15th Ed. 3.AMBOSS platform Thank You