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MEMBRANE STRUCTURE, MEMBRANETRANSPORT MEMBRANE STRUCTURE Biological membranes consists of lipids and proteins to bind with non-covalent bond. Phospholipids are the main components of biological membranes. Phospholipid = diglyceride (1 glycerole + 2 fatty acids) + phosphate group + organic molecule (e.g. choline) Membrane-models Irving Langmuir was an American chemist and Lipid-soluble substances enter the cell quickly. physicist. 1932 – Nobel prize Fats are arranged in a layer on the surface. Benzine-lipid mixture, the evaporation of petrol a molecular lipid film is formed. Petrol – soluble lipids form lipid bilayer on the surface of the water. 1925 Lipid bilayer The proteins are an integral part of cell membrane. The lipid bilayer. Partly explains the proteins, sugars, ions and other hydrophilic substances fast passage. Discovery of Electronmicroscope. The cells are covered by plasmamembrane. „Unit-membrane”model. Mosaic-like 1972 „ Fluid arrangement mosaic” modelof proteins in the membrane. Transmembrane proteins. Dr. habil. Kőhidai László FLUID MOSAIC MODEL Singer – Nicolson 1972 Membrane of erythrocyte http://www.youtube.com/watch?v=ZP3i5Q9XfTk http://www.youtube.com/watch?v=oq4Um1oV4ag STRUCTURE OF THE CELL MEMBRANE MEMBRANE PROTEINS These proteins determine the function of the membranes. The types of membrane proteins: Transmembrane proteins – It can bind to the hydrophobic part of the membrane. Peripheral membrane proteins– not directly linked to the membrane. Glycoproteins - these oligosaccharides are attached to the extracellular side of the membrane proteins. Glycosyl-phosphatidylinositol (GPI) - are covalently bonded to the membrane’s lipids. Roles: Ion channels Receptors Signal transduction Example 1: DIFFUSION THROUGHT THE CELL MEMBRANE EXTRACELLULAR SPACE MATTER TRANSPORT LIPID BILAYER MEMBRANE PROTEINS INTRACELLULAR SPACE cytoplasm water apolar molecules ions monosaccharides amino acids metabolites different mechanism: exocytosis and endocytosis DIFFUSION THROUGH THE CELL MEMBRANE TRANSPORT PROCESSES ACROSS BIOLOGICAL MEMBRANES I. TRANSPORT MECHANISM WITHOUT MEDIATOR WITH MEDIATOR PASSIVE DIFFUSION ion channels 1. 2. FACILITATED DIFFUSION carrier proteins carrier proteins 3. PASSIVE TRANSPORT 4. ACTIVE TRANSPORT II. ENERGETIC REQUIREMENTS DIFFUSION THROUGH THE CELL MEMBRANE 1. PASSIVE DIFFUSION Passive transport Without mediator direction of transport:ELECTRO-CHEMICAL POTENTIAL GRADIENT chemical potential gradient (concentration) electric potential gradient (charge) rate of diffusion: Fick’s laws mediator: no energetic requirement: no examples: hydrophobic molecules: O2, N2 small polar molecules: CO2, water, alcohol, urea, glycerol glucose, sacharose DIFFUSION THROUGH THE CELL MEMBRANE 2. FACILITATED DIFFUSION Passive transport With mediator: ION-CHANNEL direction of transport: chemical or electro-chemical potential gradient rate of diffusion: faster than that expected from Fick’s laws mediator: ION-CHANNEL PROTEIN transmembrane proteins closed / open state: no transport / transport regulation: mechanically-gated (mechanical tension) voltage-gated (potential difference) ligand-gated (ligand-binding) selectivity: size & charge of the ions energetic requirement: no DIFFUSION THROUGH THE CELL MEMBRANE 3. FACILITATED DIFFUSION Passive transport With mediator: CARRIER PROTEINS direction of transport: chemical or electro-chemical potential gradient rate of diffusion: faster than that expected from Fick’s laws mediator: CARRIER PROTEIN specifically binds the ions or molecules and promotes their transport energetic requirement: no DIFFUSION THROUGH THE CELL MEMBRANE 4. FACILITATED DIFFUSION Active transport With mediator: CARRIER PROTEINS direction of transport: AGAINST the chemical or electro-chemical potential gradient ! ENERGY IS REQUIRED mediator: CARRIER PROTEIN uniporter symporter/antiporter energetic requirement: yes ATPase transporter (ATP hydrolysis) photo transporter (light energy) coupled transporter (energy from an other transport) example: Na+-K+ pump