Bau Lec 4 Organelles PDF

FABL 201. Cell organelle 2 Prof. Dr. Noha Mahmoud Zahran Prof. of Histology & Cell Biology Faculty of Medicine, University of Alexandria [email protected]  EM sER  It consists of close network of interconnected branching tubules and vesicles. ...

FABL 201. Cell organelle 2 Prof. Dr. Noha Mahmoud Zahran Prof. of Histology & Cell Biology Faculty of Medicine, University of Alexandria [email protected]  EM sER  It consists of close network of interconnected branching tubules and vesicles.  The membranes have smooth surface as it lacks the attached ribosomes.  The membranes of the sER are continuous with that of rER.  Smooth endoplasmic reticulum (sER) Functions 1. Synthesis of membrane lipids (the phospholipids and cholesterol). 2. Synthesis of steroid hormones. 3. Synthesis of glycogen in liver. 4. Detoxification and conjugation of toxic substances (alcohol and drugs). 5. Regulation of calcium ions during muscle contraction: (sarcoplasmic reticulum).  Abundant in rER sER Liver cells. Liver cells Protein synthesizing and secreting cells Steroid- secreting cells (adrenal cortex, (pancreatic acini, fibroblasts & plasma testis and ovary). cells). Intended learning outcome: By the end of this lecture student are able to: describe the LM and EM structure of Golgi apparatus and lysosomes. describe pathways for intracellular digestion by lysosomes. relate the structure of Golgi apparatus and lysosomes to their specific functions. illustrate histological diagrams of Golgi apparatus and the different pathways of lysosomal function. Identify histological structure of mitochondria. Describe and differentiate between types of cell transport through cell membrane. rER: Function- Where!  Membrane bounded organelles Golgi apparatus Lysosomes Mitochondria. The cell organelle. Its histological structure: is investigated by using: 1) The LM. 2) The EM. 3) A molecular study. Site and relation of Golgi appratus Golgi apparatus by LM (H&E- Silver stain) Golgi apparatus- EM Molecular structure of Golgi appratus Golgi apparatus- where!  Golgi apparatus- Functions: 1- Post-translational modification of secretory proteins 2- Packaging,sorting & targeting of proteins: Hydrolytic enzymes ►► lysosome Secretory granules ►► exocytosis 3. Membrane renewal &recycling Lysosomes. Lysosomes. Membrane bound. Hydrolytic digestive enzymes. Intracellular digestion. LM: Immunohistochemical staining EM: Various shapes &sizes Unique glycocalyx???  Lysosomes Membrane- bounded containing “acid” hydrolytic enzymes ►►(Intra cellular digestion) EM  Lysosomes: Functional types 1- Multivesicular bodies 2- Phagolysosomes =phagosome 3- Autophagosomes 4- Residual bodies 5- Lipofuscin granules = age pigments-where? Auto phage vacoule Time for questions? The site of packaging of different molecules into vesicles is: a. lysosomes b. ribosome c. golgi apparatus d.rER which of the following structure-function pairs is mismatched: lysosome--intercellular digestion golgi body-secretion of cell products. ribosome-protein synthesis..rEr-detoxification  Mitochondria. The mitochondria are the powerhouses of the cell as they are the sites of adenosine triphosphate (ATP) production. LM picture contribute to the cytoplasmic eosinophilia because of the large amount of membrane they contain. Mitochondria can be visualized in tissues by using special stains e.g., silver stain.  Mitochondria. EM picture - Mitochondria are membrane-bounded organelles, absent in RBCs and terminal keratinocytes of skin epidermis. - surrounded by two membranes: - outer and inner, which define two mitochondrial compartments;  The intermembranous space, the compartment located between the two membranes.  The matrix space, the compartment enclosed by the inner membrane. Mitochondria. The outer membrane: it is smooth and porous. It allows easy passage of small molecules due to the presence of specific transmembrane proteins called mitochondrial porins. The inner membrane: It is folded into numerous cristae which greatly increase its total surface area; the number of cristae is greater in cells of greater demand for ATP as in cardiac muscle fibers. Mitochondria. Most mitochondria have flat, lamellar cristae cells that secrete steroids contain tubular cristae. It is highly impermeable to ions and small molecules due to presence of specific phospholipid called cardiolipin. It contains the enzymatic (respiratory chain enzymes) and the ATP synthase. Matrix space - is surrounded by the inner mitochondrial membrane. It contains the following:  Numerous soluble enzymes involved in specialized mitochondrial functions as citric acid cycle.  Mitochondrial DNA and few ribosomes.  Matrix granules that store calcium ions (Ca 2+) thus play a role in mitochondrial regulation of Ca 2+ intracellular concentration. Intermembranous space it contains specific enzymes as cytochrome c which is an important factor in initiating apoptosis (programmed cell death). Transport across the cell membrane A) Small molecules B) Large molecules (Micromolecules) (Macromolecules) I-Passive transport I-Endocytosis -1. Pinocytosis 1) Simple diffusion -2. Receptor mediated 2) Facilitated diffusion -3. Phagocytosis 3) Osmosis II-Active transport II- Exocytosis -1. Regulated secretion -2. Constitutive secretion Transport of micromolecules across the cell membrane Passive Active **  Spontaneous.  Not spontaneous.  No energy is needed.  Requires energy.  Along concentration gradient.  Against concentration gradient.  Not all use protein receptors.?  All use protein receptors.  Types:  Types: 1. Simple diffusion. 1. primary. 2. Facilitated diffusion. 2. secondary. 3. Osmosis. Passive & Active transport of Micromolecules  B) Transport of Large molecules (Vesicular transport) The macromolecules are lipid insoluble and can not pass through the protein channels.  Transport of macromolecule (Vesicular) I-Endocytosis Inside = internal  Active process.  Uptake of macromolecules from extracellular space to inside the cell.  Involves invagination of the cell membrane to form membrane- bounded vesicle. 3 mechanisms: -1 Pinocytosis (cell drinking) -2 Receptor–mediated endocytosis -3 Phagocytosis (cell eating) 1. Pinocytosis  Pinocytosis -A non-selective process. (Does not need receptors on the surface). - Involves uptake of fluid containing ions & small protein molecules which are water soluble.  Involves invagination of the cell membrane: to form membrane- bounded vesicle. - The pinocytotic vesicles are small and have smooth surface. Occurrence of pinocytosis: in nearly all cell types; most evident in the endothelium of blood vessels*. 2. Receptor mediated endocytosis  A highly-selective process. WHY? As it involves the uptake of a specific substance (ligand) by a specific cell that has receptors for these substances. e.g Protein hormone  Receptor mediated endocytosis In a specific cell: It involves: 2. Formation of coated pits: = regions of the cell membrane at which the receptors are concentrated & coated by a protein called clathrin. 3. & 4. Invagination of the clathrin-coated pits giving rise to small spinous clathrin- coated vesicles containing the ligand. 5. Uncoating of the vesicle. The clathrin coat will be lost and recycled for reuse. 6. The uncoated vesicle are delivered to the lysosomal pathway (See later)  3- Phagocytosis (cell eating)  Ingestion of large solid particles, such as bacteria.  A form of receptor-mediated endocytosis.  But, it does not involve formation of coated pits or vesicles.  It occurs in special types of cells, known as phagocytic cells which have receptors on their surfaces that recognize and bind the foreign particles.  Pseudopodia are formed to engulf the particle, followed by fusion of the membrane to internalize the particle into the cytoplasm forming a membrane-bound phagosome.  The contents of the phagosome are then digested through the lysosomal pathway. * Phagocytosis Phagocytosis  II. Exocytosis External = outside Release of cell products into the extracellular environment. What happens in the process of exocytosis?: A vesicle moves from the cytoplasm to the cell membrane, fuses with it and discharges its contents. Types of exocytosis 1- Regulated secretion: (Stimulus – dependent) - Stored membrane – bounded secretory granules are formed. - A stimulus (hormonal or neuronal) will move the vesicles to the surface. - The vesicles fuse with the cell membrane to pour their contents outside the cell. - e.g. The release of the digestive enzymes of cells - of the pancreas. 2. Constitutive secretion: * Non- stimulus dependent: WHY? as the secretory products leave the cell immediately after their synthesis. i.e. No need for a stimulus to move the vesicle to the surface for exocytosis. i.e. the secretion is released continuously through the secretory vesicles that fuse with the cell membrane. * No stored secretory granules. - e.g. Release of antibodies by plasma cells.* Membrane recycling During the vesicular transport, the cell membrane is maintained. How?  The excess membrane added to the cell membrane by exocytosis is constantly recycled again into the cytoplasmic compartments by endocytosis. References. Histology and cell biology by medical staff Alexandria University. Mescher ALJLCUa. Junqueira's basic histology: text and atlas. 16th ed. New York: McGraw-Hill Medical; 2021. Gartner LP. Textbook of Histology. 5th ed. Philadelphia, PA: Elsevier; 2021. Ross MH, Pawlina W. Histology: A text and atlas; with correlated cell and molecular biology. 7th ed. New York: Lippincott Williams & Wilkins; 2016.