Cell Membrane Lecture 2 PDF

lecture 2 The cell membrane By Dr. Dr Doaa Khaled Lecturer of HISTOLOGY & CYTOLOGY, Faculty of Medicine , Helwan University  Objectives 1- Recognize some cell terminology 2- Describe cell size, Types and components 3- Describe Cell membrane: (L M & EM) 4-Out...

lecture 2 The cell membrane By Dr. Dr Doaa Khaled Lecturer of HISTOLOGY & CYTOLOGY, Faculty of Medicine , Helwan University  Objectives 1- Recognize some cell terminology 2- Describe cell size, Types and components 3- Describe Cell membrane: (L M & EM) 4-Outlines cell membrane function.  Cells Tissues Organs Systems  Cell Cell is the:: Structural and Functional unit of any tissue. it needs magnifications and   Staining for light microscopy Tissues and their components are colorless Need to be stained Stains color different components with different colors Cytoplasm = Basic ++ Nucleus = acidic --  haematoxylin and Eosin Stain (H & E) Is the most commonly used stain in routine histology examination H & E gives the best differentiation between tissue components 1. Hematoxylin (H): Blue Basic stain Binds to acidic components of the cell e.g nuclei 2. Eosin (E): Pink Acidic stain Binds to basic components of the cell e.g cytoplasmic proteins  THE CELL Types: Different types of cells. Skin cells are different than muscle cells, or bone cells, or blood cells. The size : range from microns to millimeter, based on the type of function that it performs. Shape: spherical, rod, flat, concave, curved, rectangular, oval …..etc.. Types of cells  Structure of the cell 1- Cytoplasm (cytosol, organelles and inclusions). 2- Nucleus.  I) The Cytoplasm colloidal solution, called the cytoplasmic matrix or cytosol, in which some bodies are suspended ----- granular appearance. The suspended bodies of the cytoplasm (2 groups) 1-the cytoplasmic organoids (organelles) 2-the cytoplasmic inclusions.  What is the Cytosol ? It is the fluid component of cytoplasm that contains : - enzymes like ( enzymes used GLYCOLYTIC PATHWAY). - mRNA, transfer RNA, enzymes, Oxygen, CO2. - (ions & salts), waste products.  The cell (cytoplasmic) organoids (organelles) Definition: living , essential to the vitality and function of the cell. Types: A) Membranous cell organoids (organelles)... 1- Cell membrane (plasmalemma) 2- Endoplasmic reticulum 3- Golgi apparatus 4- Mitochondria 5- Lysosomes 6-coated vesicles 7- endosomes 8- peroxisomes B) Non-membranoucellorganoids(organelles)... 1- Ribosomes and polyribosomes 2- Microtubules ( centroiles, cilia and flagella) 3- Filaments Membranous Cell Organoids  A) Cell membrane By L/M: By E/M MOLECULAR STRUCTURE FUNCTION in relation to histology  1) The cell membrane and the cell coat By L/M: - 7.5 - 10 nm in thickness. - Too thin to be seen with LM.  By E.M.: 1-Trilaminar or UNITE membrane. 2- Two electron dense layers separated by a lucent intermediate one. 3-The outer surface covered by the cell coat (glycocalyx).  The molecular structure of cell membrane 1) Lipids (Phospholipid molecules + cholestrol). 2) Proteins. 3) Glycoproteins & Glycolipid. 1) Phospholipid molecules. - Two rows (BILAYER) of phospholipid molecules. - Each phospholipid molecule is composed of: Polar (hydrophilic) phosphate head: Non-polar (hydrophobic) tail (two fatty acid chain) 1- hydrophilic polar end (water attracting): Directed towards aqueous solutions. Arranged at the outer and inner(cytoplasmic) surfaces. 1- hydrophobic polar end (water repelling): located in the middle region away from water and facing each other.  Nb : The dark lines (The electron-dense lines) observed by electron microscope. Caused by the deposit of Osmium Tetroxide (used in EM preparation) in the hydrophilic portions of the phospholipid molecules.  2- Cholesterol Site : Present among the closely – packed phospholipid fatty acids. Function: it has a stabilizing effect on the membrane and regulating the fluidity of cell membrane in body temperature N.B: Without cholesterol, cell membranes would be to permeable to some molecules.  3) Protein molecules )50%) 1- The lipid in the membrane is incorporated with Ptns molecules which are of Two types: a) The integral (intrinsic) membrane proteins. b) The peripheral (extrinsic) membrane proteins. a) The integral (intrinsic) membrane proteins. 1- (Transmembrane protein).Span the membrane from one side to the other 2- Others are small & partly embedded in the hydrophilic region of lipid bilayer called (=carriers). 3- The integral proteins requires detergent (strong treatment) to disrupt the lipid & remove them from the cell membrane. b) The peripheral (extrinsic) membrane proteins. - Bound to the one of the 2 membrane surfaces especially the cytoplasmic side of the lipid bilayer. - This type of (Ptns) can be removed easily with salt solution (with mild treatment) 4) Glycoprotein and glycolipids molecules: - Projecting from the outer surface of the membrane to form the cell coat (glycocalyx). - Fuzzy layer by EM. Chemically formed of : a) Glycoptns: oligosaccharide chain+ ptn molecule. b) Glycolipids: oligosaccharide chain+ phospholipid molecule. Function of cell coat: Its integral ptn components act as a receptors share in important interactions such as: Cell adhesion Cell recognition Hormones response. What is the function of cell membrane? 1- Selective barrier (semipermeable) One important role of cell membrane is to keep constant the ion content of cytoplasm, which differs from that of extracellular fluid 2- membrane transport &selective permeability : (physiology ) 3- Communication Cells need to communicate with one another to regulate their growth, division, and to coordinate their functions. Some of the integral membrane proteins act as membrane receptors that recognize signaling molecules from other cells 4- Vesicular transport (bulk transport) 1)Endocytosis & exocytosis. 2) Receptor-mediated endocytosis 1) Endocytosis ( Fig 2-6 p. 11&12) A- Phagocytosis ????? B- Pinocytosis?????? A- Phagocytosis Exocytosis Bulk movement of substance from inside outside the cell by fusion of secretory vesicles with the plasma membrane e.g: release of neurotransmitter By nerve cell. 2- Receptor mediated endocytosis (highly selective transport) 1- Receptors ( some integral membranous Ptns) for specific molecules( ligands) such as low- density protein & protein hormones..These receptor present at cell surface. 2- Binding of these specific molecules (ligands) to its receptor causes widely dispersed receptors to accumulate in coated pit 10/7/2024 3- On other hand the coating on the cytoplasmic surface is composed of many proteins mainly clathrin. 4- The coated pit invaginates and pinched off in the cytoplasm as coated vesicles. 5- So The coated vesicle carries the specific molecule (ligand) & its receptor into cell.  The clathrin molecule separate from the coated vesicles & recycle back to the cell membrane ----- for formation of new coated pits.  Nb : Endocytosis of low-density lipoproteins (LDL) is an important mechanism that keeps the concentration of LDL in extracellular body fluids low to keep the cholesterol in blood in low level Then the LDL is delivered to lysosomes where it is degraded, and its cholesterol is released for use in the synthesis of membranes 2-Other vesicles containing ligands may move to and fuse with cell surface and release the ligands outside in the process of (transcytosis) LDL Endocytosis Endocytosis &Exocytosis Transcytosis Capillary Exchange- Transcytosis  Membrane trafficking Portions of the cell membrane become part of the endocytotic vesicles during endocytosis. …during exocytsis, membrane is returned to the cell surface. The process of membrane movement and recycling is called membrane trafficking…… This process is important for cell maintenance & health & preserving membrane area  TEST YOUSELF Which of the following is best describes the cell membrane? A- It is well demonstrated by H&E B- Formed mainly of glycoproteins and glycolipids. C- Covered from inside with cell coat D- it is thickness 7-10 nm  TEST YOUSELF Which of the following regulating the fluidity of the cell membrane? A- Cell coat B- Phospholipids C- Proteins D- Cholesterol Reference Chapter 2, The Cytoplasm Junqueira's Basic Histology Text and A tlas, 16e 60 GOOD LUCK