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Download Plasma membrane Dr.Shayma`a Jamal Ahmed
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Transcript
. At the end of this lecture the student will be able to: Define the cell membrane. Describe the structure of cell membrane. Determine the functions of cell membrane. Recognize to the mechanisms of transport. Compare between the Exocytosis & Endocytosis Which is called also plasma Membrane or Cytoplasmic Membrane . It is a biological membrane, it is surrounding and separating the interior components (which are alive)of all cells from the outside environment (which is nonliving). The cell membrane is flexible and allows a unicellular organism to move. Balanced internal condition of cells Also called equilibrium Maintained by plasma membrane controlling what enters & leaves the cell Protective barrier Regulate transport in & out of cell (selectively permeable) Allow cell recognition. Provide anchor sites for filaments of cytoskeleton. Provide a binding site for enzymes Interlocking surfaces bind cells together (junctions) Contains the cytoplasm (fluid in cell) The plasma membrane (cell membrane) is made of two layers of phospholipids. The membrane has many proteins embedded in it. The arrangement of protein & lipid molecules with in the membrane may suggest different models. The most accepted model is the Fluid-Mosaic model. In 1972, Singer & Nicolson revised the model in simple way: They proposed that: the globular protein are inserted of the lipid bilayer, with their nonpolar segments in contact with the nonpolar interrior of the bilayer & their polar portions stick out from the membrane surface. A. Mosaic: an object comprised of bits and pieces embedded in a supporting structure 1. membrane lipids form the supporting structure 2. membrane proteins provide the bits and pieces 3. both lipids and proteins may be mobile or 'fluid' B. Membrane lipids: the supporting structure 1. phospholipids 2. glycolipids 3. cholesterol C. Membrane proteins: the bits and pieces 1. integral (intrinsic) proteins 2. peripheral (extrinsic) proteins 1. a. Lipids : bilayer of phospholipids Hydrophilic heads - P04 end "water" "loving" attracted to water on inner/outer parts of cell b. Hydrophobic tails - fatty acids "water" "fearing" attracted to each other on inside of bilayer Diagram of the arrangement of amphipathic lipid molecules to form a lipid bilayer. The yellow polar head groups separate the grey hydrophobic tails from the aqueous cytosolic and extracellular environments. c. Glycolipids - some carbohydrates attached to outer lipids (involved in cell to cell recognition) d. Cholesterol - regulates fluidity of membrane 2. proteins: interspersed throughout the membrane. 1) 2) 3) 4) 5) 6) Receptors:- hormones ,neurotransmitters. Enzymes: - reactions in & out of cell. Transport :- ions and molecules. Intercellular junctions. Cell-cell recognition. Cytoskeletal and extracellular matrix attachment. 1- Integral proteins: - inserted into the bilayer (transmembrane - across entire bilayer). 2- Peripheral proteins: - on inner & outer surface. 3- Glycoproteins: - carbohydrates on outer surface. glycocalyx - outer carbohydrate coat (cell recognition and identification). . 11- lipids can pass through the cell membrane easily. 2- Small molecules and larger hydrophobic molecules move through easily. e.g. O2, CO2, H2O 3- Ions, hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own