Class 2 Cellular Membrane by LS 2024 PDF

Class 2 Biological Membrane Fluid Mosaic model - Experimental Evidences that make up the model - Diffusion of membrane components - Types of transmembrane proteins - Integral proteins that mediate interaction - Membrane fusion Biological Processes - Characteristics of Biological Membranes (...

Class 2 Biological Membrane Fluid Mosaic model - Experimental Evidences that make up the model - Diffusion of membrane components - Types of transmembrane proteins - Integral proteins that mediate interaction - Membrane fusion Biological Processes - Characteristics of Biological Membranes (Goter y Grendel 1928) Extraction of erythrocyte membrane ghosts. 1- They are flexible Shape Changes 2- They seal themselves, Membrane fusion. Biological processes Exocytosis Phagocytosis Fecundation Route of infection  Non-covalently assembled phospholipid monomers Anphipatic molecule Saturated Fatty Acid Unsaturated fats with double bonds In the hydrocarbon chain Structural model of fluid mosaic  Nomenclature of the faces of the cell membrane Red: Cito-plasmatic Black: Exo-plasmatic  Physical Properties of the Membrane (evidence) 1- The phospholipid membranes pure are similar to natural ones. 2- Mixture of phospholipids with a similar composition like natural membranes form bi-layer flat or liposomes provide spontaneous way (Fig 5-32). 3- Evidence of the structure of bilayer by X-ray diffraction, of the myelin membrane Experimental formation of pure phospholipid bilayers Solvent Chloroform:methanol evaporation 1:3 Black lipid membranes Myelin membrane analysis by X-ray diffraction. They represent less than 10% of the proteins = Despicable 4- Selectivity Permeable to polar solutes 5- There is 5 to 8 nm (50 to 80 A) thick and the appearance is trilaminar (E.M.) The membrane includes Transport of organic and inorganic solutes Cellular Re-arrangement Receptors sensitive to extracellular signals (molecular changes) Molecular adhesion between cells Fig. 1: Table of lipid composition: Each type of membrane has characteristics of lipids and proteins. The relative proportion of them depends on the membrane. What is the common between the molecules? The angularity of the acyl chains gives fluidity to the membrane + cholesterol The Last classs  Proportion of lipids in different organelles of a hepatocyte What is the lipid more commun in plasma membrane? impervious to certain molecules Architecture of the membrane : Fluid Mosaic Model. Fig.(Singer and Nicolson en 1972) Experimental Evidence E.M. : Trilaminar Structure (Fig. 12-1) Chemical Studies: Permeability Physical Studies: X-Ray Diffraction (Fig. 5-33) Trilaminar Structure two electron dense lines trilaminar appearance (Transmission Electron Microscopy) The integral proteins float in a sea of lipids and they bound by hydrophobic interactions (Van der Walls) with non-polar a.a chains. Lateral movement Proteins The carbohydrate motifs are exposed to the extra cellular face. Lipids Glycoproteins y Glycolipids. Proteins can protrude On one side of the membrane Domains exposed on both sides. Orientation of the proteins is Asymmetric in the bilayer. WHY? Experimental evidence that forms the model: 1- A lipid bilayer is the structural base of the membrane Glycerolfosfate Sphingolipids Are insoluble in water Steroles (Glycerol) Mixing the lipids with water spontaneously forms aggregates (liposomes), Figure of Micelle 2- The lipids of the membranes are in constant movement: Flip-Flop Fig. 12-6. Mobility of lipids in membranes. Lipids and sterols have a high degree of mobility in the plane of the membrane.  Movement of lipids depend A- Thermal movement of fatty acid groups (heat effect). B- Lateral diffusion of molecules. Individual of one side of the bilayer. Transition Temperature: As the temperature rises from gel (paracrystalline) to liquid (depending on the size of the hydrocarbon tails and the number of unsaturated lipids) double bonds. C- Trans-bilayer or Flip-Flop movement: Individual movility of molecules between the two sides of the bi-layer is very slow. Fast by Flippase (Enzime) Transition Temperature Please, can you compare the time of flip-flop difusión, when the flippase is present? “The degree of fluidity depends on the lipid composition and temperature”. 1- Temperature At lowTemp. Small movements (Crystalline arrangement) Above certain temperature rapid movement Transition Temperature: It is the temperature at which the paracrystalline solid changes to fluid and is characteristic of each membrane. 2- Fatty acids Saturated Packaged in paracrystalline Temp. of Transition Unsaturated They interfere in the packaging and gives more fluidity. 3- Sterols The flat structure determines the Temp. Interferes with fluency of Transition (T.T.) The rings reduce the freedom of the Fatty acids tails. Reduces fluency  “Experiments that evidence movements”: Proteins spread laterally in the sea of lipids Fig. 5-35 Fusion of mouse cells with human cells + Fig. 12-7 Species-specific anti-bodies and Fluorescence - Image of FRAP, (This method can also be used to measure the lateral diffusion of membrane proteins) - Some membrane proteins associated with a large aggregate on the surface of the organelle cell, where the protein does not move relative to others (Example: acetylcholine receptors on the synaptic neuron).  In 1970, David Frye and Michael Eddidin, Demonstration of lateral diffusion of membrane proteins. fluorecein rhodamine Labeled with Abs against Human Prot. and Prot. mouse Dispersion of proteins and showed fluorescence pattern mixed Fusion of a mouse and a human cell, followed by the diffusion of membrane components in the plane of the plasma membrane. Blue and red fluorescent markers are completely intermixed after several hours Membrane Lipid Movements Labeling a phospholipid with a chromophore such as rhodamine Model of the fluid mosaic What did it prove? FLIP-FLOP Movement What did it prove? Erythrocyte membrane proteins Spectrin (cytoskeleton) Ankyrin (anchor) Protein Binding Network - Viewing the membrane E.M. + Tissue staining with Osmium Tetraoxide Density to ME Cryofracture technique - (Fig. 5-36) + Scanning microscope Cytosolic internal face release the bilayer membranes Extracelular external face Restricted movement of the erythrocyte chlor-bicarbonate exchanger Separation of the membrane bilayer by the freeze-fracture technique What did it prove? The membrane integral membrane proteins remain related to either side of the membrane subjected to this technique Micrograph of the erythrocyte membrane Membrane has functions common to all cells Carriers Glyco- proteins and gluco- Proteins lipids form unions between cells tissue Metabolite exchange maintain ionic concentration Membrane integral proteins Types of transmembrane proteins: Fig. 12-9 (son 6) I A single stranded transmembrane. II III Multiple transmembrane helices in a single polypeptide IV Transmembrane domains of various polypeptides, assembled in Types of transmembrane proteins: Fig. 12-9 ( They are 6) V They bind to the bilayer by covalent bonds (GPI) VI Proteins having both transmembrane helices and lipid-anchored (GPI) glycosylphosphatidylinositol Integral proteins mediate cell-cell and adhesion (extracellular matrix) interactions. Lipid bonds of the membrane proteins The protein TRAP is marked and the distribution is homogeneous on the membrane, but when the parasite contacts the cell, the protein is concentrated in a capping to penetrate Maria M. Mota y Ana Rodriguez (2001) Microbes and Infection, 3, 1123-1128 Mechanisms of Invasion of Plasmodium into Hepatic Cells Please, Explain the table Integral proteins mediate Cell-Cell interactions and adhesion (Extracellular Matrix , EM). Family of Integral Proteins 1- Integrins (heterodimer): Protein + Extracellular Matrix 2- Cadherin: Prot. + adhesion 3- Selectins (Ca+) : adhesion (coagulation) 4- N-CAM (similar to Igs domains) Four examples of types of integral proteins that participate in cell-cell interactions. Membrane fusion Processes Requirements for the fusion of 2 membranes: 1- They recognize each other. (SNARES THEORY) 2- The surfaces of the membranes approach removal of H2O from the heads of Lipids. 3- The membranes are disrupted locally to form a continuum membrane. 4- Two bilayers are fused to form one. 5- The fusion process is fired at an appropriate time in response to a specific signal. Lipid rafts: This are areas with concentrated recepts Rich in sphingolipids and cholesterol Discussion of paper about Fluid Mosaic Model Answer the following questions based on the Singer and Nicolson model article: 1- How do membranes exist, in which states? 2- What is the purpose of this review? 3- How did Singer and Nicolson see the model? 4- Say an evidence for the bilayer? 5- How can membrane proteins be associated? 6- In the model, which molecules can be in constant motion? 7- What types of movements occur in this model? 8- What do you mean by FLUIDITY? 9- What is an amphitropic protein? Questions about the plasma membrane (Reference to Exam) How are proteins inserted into the plasma membrane? What is the function of recognition proteins in the plasma membrane? What are channel proteins? Why is the plasma membrane a bilayer? Do membrane proteins move? Evidence with an experiment What are the two relevant lipid components of the plasma membrane? This week Will group A to Laboratory