Lecture 2 Cytoplasmic Organelles 1 PDF

Lecture 2 histology cell organelles Prof. dr. Manal shaaban Hafez Professors of Histology and Cell Biology Prof. dr. Noha Abdel Latif Professors of Histology and Cell Biology Faculty of Medicine, Fall 2024-2025 Galala University...

Lecture 2 histology cell organelles Prof. dr. Manal shaaban Hafez Professors of Histology and Cell Biology Prof. dr. Noha Abdel Latif Professors of Histology and Cell Biology Faculty of Medicine, Fall 2024-2025 Galala University gu.edu.eg NORMAL STRUCTURE OF HUMAN BODY MODULE Course Code (BMS 111 )  Lecture 2 CELL STRUCTURE Reference Junqueira's Basic Histology, Text and Atlas. Mescher AL, 15th Edition, 2018.  Learning Objectives By the end of this Lecture, you should be able to: Classify contents of cytoplasm. Classify cellular organelles as regard the presence of membranes Define different cellular organelles Describe microscopic structure of cell membrane Explain molecular structure of cell membrane Describe functions of cell membrane and different types of cellular transport Describe microscopic structure and function of mitochondria. The Cell  The Cell Definition: It is the structural and functional unit of all Living tissues. Structure of cells: Each cell is composed of the following two main parts: 1. The cytoplasm. 2. The Nucleus.  THE CYTOPLASM 1- Matrix: It is the viscoid colloidal solution. It is made of proteins, carbohydrates, lipids, enzymes, minerals, ions and water. 2. Organelles 3. Inclusions 1. Living structures. 1. Non living structure. 2. Permanent components of the 2. Temporary components of the cytoplasm. cytoplasm. 3. Not essential for life of cells. 3. Essential for life of each cell. 4. Metabolically inert as they do not contain enzymes. 4. Metabolically active because they contain enzymes. 5. Not in all cells. 5. Present in all nucleated cells. 6. Have vital functions. 6. Result from cell vital activity  Cell Organelles Membranous Non-membranous ▪ Covered by membrane ▪ Uncovered by membrane Cell (Plasma) membrane Ribosomes Mitochondria Proteosomes Rough endoplasmic reticulum (rER) Cytoskeleton Smooth endoplasmic reticulum (sER) Golgi apparatus Lysosomes Peroxisomes 8  The Membranous Cell Organelles 1. THE CELL (PLASMA) MEMBRANE Definition: It is the outermost covering of the cytoplasm. The light microscope (LM): It cannot be demonstrated because it is very thin. The electron microscope (EM): it shows trilaminar appearance Its outer and inner layers appear as dark lines, & middle layer appears as a light area. Its outer layer appears fuzzy. Staining: Could be stained red by PAS stain. Lipid Component Phospholipid bilayer Cholesterol Protein Component (50%). Peripheral proteins Integral proteins Carbohydrate Component Faculty of Medicine 10  Lipid Component 1- Lipid Component: (30%) It consists of a- Phospholipid molecules: They are arranged into 2 layers (bilayer). Each molecule has a polar and a non-polar end. The polar end (head): It is hydrophilic and directed outwards, so the heads are found on the outer and the inner (cytoplasmic) surfaces of the cell membrane. The non-polar end (tail): It is hydrophobic and directed inwards, where the tails of the two layers interact with each other forming a stable center for the cell membrane. They face each other in the central part of the cell membrane. Functions: Selective permeability of cell membrane; allow passage of small, & fat-soluble substances  cell membrane appears trilaminar by EM? Due to deposition of osmium on the hydrophilic heads Faculty of Medicine 12  Fill gaps between the hydrophobic fatty acid tails. Functions: ✓ Stability of the membrane. (Restricting movement of phospholipid molecules) ✓ Modulating membrane fluidity. Faculty of Medicine 13 Molecular Biology  Protein Component 2. Protein Component: (60%) It consists of a. Extrinsic (Peripheral) protein: It is loosely attached protein molecules, on both surfaces of the membrane. b. Intrinsic (Integral) protein: it is embedded in the lipid bilayer Most of Integral molecules are large enough to cross the membrane (Trans-membrane proteins). These large Integral proteins act as pathways for ions and molecules (Channel proteins). Functions of transmembrane proteins: ✓ Channels for transport of ions and water ✓ Carriers for transport of small polar molecules as glucose and ions as Na/K pump. The molecular structure of cell membrane Sugar chains: oligosaccharide chains linked to: Membrane proteins: glycoproteins Membrane phospholipids: glycolipids ✓ located on the outer surface only of plasma membrane. Functions: Cell to Cell adhesion. Cell identification. Receptor for ligands. Faculty of Medicine 17 See physiology for more details Faculty of Medicine 18  3 Bulk transport Endocytosis: Active movement of substance into the cell by forming vesicles. 3 types Phagocytosis Pinocytosis Receptor mediated endocytosis Exocytosis: Active movement of substance from inside to outside of the cell by forming vesicles Faculty of Medicine 19  Phagocytosis (Cell eating) Pseudopodia extended from the cell membrane to surround solid particle e.g. bacterium. ✓ Ends of pseudopodia fuse enclosing bacterium in intracellular vacuole called phagosome. ✓ Phagosome then fuses with lysosome for digestion of its contents. ✓ Ex: WBCs engulfing bacteria. Faculty of Medicine 21  Pinocytosis (Cell drinking) Smaller invagination (pocket) of cell membrane formed to surround extracellular fluid. ✓ Ends of pocket fuse then detach off inwardly from cell membrane forming Pinocytic vesicle ✓ Pinocytic vesicle then fuses with lysosome for digestion of its contents. ✓ Ex: endothelial cells of blood vessels. Faculty of Medicine 22  Receptor mediated endocytosis Receptors (Integral proteins) accumulate at the cell membrane to bind specific ligands. ✓ They associate with other proteins on the cytoplasmic side called Clathrin to form coated pit. ✓ The coated pit invaginates gradually and pinches off, forming coated vesicle containing ligands and their receptors. Clathrin is dissociated and recycled. ✓ Ex: uptake of hormones as GH & uptake Facultyof LDL. of Medicine 23  Medical application Dwarfism Caused by GH deficiency OR Non-functioning GH receptors at cell membrane of target cells (Level of GH is normal)  Cytoplasmic (secretory) vesicle migrates & fuses with the cell membrane. ✓ Release of contents into extracellular space. Faculty of Medicine 25  Definition: ✓ Membranous organelles responsible for cell respiration & energy production. (Power-houses of the cell). Site: all cells expect RBCs. Number: ✓ More in active cell as liver cell (1000/cell). Histological structure: L.M.: H&E: Cytoplasmic acidophilia (If abundant). (Large number of basic membrane proteins)  SP. stain: appear as granules or rods with Fe Hx & Janus green stains. E.M.: ✓ Oval or rounded vesicles. ✓ Surrounded with two membranes separated by intermembranous space. Outer membrane Inner membrane Smooth & porous ✓ Folded into Cristae Contains transmembrane surface area for attachment proteins called Porins of "ATP synthase“ enzyme (forms ATP in oxidative phosphorylation) Permeable to small molecules less permeable (selective)  E.M.: ✓ The mitochondria, is filled with semifluid called Matrix; contains: - Oxidative enzymes of citric acid cycle. - Mitochondrial DNA , RNA & few ribosomes. - Dense granules rich in Ca2+ (catalysts). Functions: Power Houses: produce ATP. Self-Replicating Organelles: by simple fission. (Mitochondria can synthesize some of their structural proteins by their own DNA & RNA) ✓ Mitochondria regulate the metabolism of calcium ions. ✓ They contain DNA which carries some genetic characters ✓ They can form proteins for themselves. ✓The protein of mitochondria is formed by its own ribosomes N.B. Mutations of mitochondrial DNA cause muscular dystrophy disease.  Medical application Mitochondrial Myopathies Defect in mitochondrial enzymes leads to failure to produce ATP which is needed for all vital activities e.g muscle contraction leads to muscular weakness. Mitochondrial DNA is always inherited from the mother Resulting in maternal transmission of diseases of energy metabolism Faculty of Medicine 30 Any questions?  Question No 1 As regarding transport of substances across the cell membrane, protein hormones enter the cell by which one of the following mechanisms? a. Passive diffusion. b. Facilitated diffusion. c. Phagocytosis. d. Receptor mediated endocytosis. e. Pinocytosis.  Question No 2 Which of the following cell membrane structure is considered the hydrophilic area of the cell membrane? a. Phospholipid heads. b. Phospholipid tails. c. Peripheral proteins. d. Cholesterol molecules. e. Glycocalyx.  Question No 3 Which one of the following cell membrane components is responsible for modulating membrane fluidity? a. Phospholipid heads. b. Phospholipid tails. c. Cholesterol molecules. d. Transmembrane proteins. e. Peipheral proteins.  Question No 4 Which of the following is a characteristic feature of mitochondria? a. Are non-membranous organelles. b. Serve as storage sites of proteins. c. Can be stained with Ag. d. Are double- membrane organelles. e. Are numerous in RBCs. Thank You gu.edu.eg