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Biophysics I - OSMOSIS 04/11/2014 Andrea Vig University of Pécs, Medical School, Department of Biophysics 28/10/2014 BROWNIAN MOTION OSMOSIS, MEMBRANETRANSPORT OVERVIEW – DIFFUSION random thermal motion of particles DIFFUSION due to the non-uniform (inhomogeneous) distribution of particles net transport of particles (Brownian motion) occurs from a region of higher concentration to a region of lower concentration which continues until the distribution of particles is uniform (homogeneous) FICK’S 1st LAW (spatial description) ∆𝒄 Onsager’s equation (linear, irreversible processes): J=XL The flow density of the extensive quantity (J) 𝑱 = −𝑫 is linearly proportional to the gradient of the intensive quantity (X) ∆𝒙 DIFFUSION COEFFICIENT: Stokes-Einstein equation 𝒌𝑻 𝑫= 𝟔𝝅𝜼𝒓 FICK’S 2nd LAW (spatial & temporal description) ∆𝑐 ∆( ) ∆𝑐 = 𝐷 ∆𝑥 ∆𝑡 ∆𝑥 1 Biophysics I - OSMOSIS 04/11/2014 OSMOSIS IN THE KITCHEN Experiment: place a dried leaf of salade into water before Osmosis in the k itchen.mp4 after (3-4 hours) Observation: the leaf of salad becomes bigger and looks fresh again OSMOSIS Experiment: place an egg into corn syrup then into water WATER CORN SYRUP Observation : the egg shrinks Observation: the shrinked egg gains its original size, and it continues to get even bigger after before before after Experiment: fill a small-size semi-permeable bag with sugar dissolved in water, and placed in a water filled container Observation : the bag is swelling, the water surrounding sugar solution water it remains pure, sugar solution has been diluted before after 2 Biophysics I - OSMOSIS 04/11/2014 What is the difference between the „ink” experiment and the „salade/egg/sugar” experiment? OSMOSIS 1. SOLID (non-permeable) WALL (as Fick’s experiment) fluid→gas (no complicated molecular interactions) A+B components, we usually ignore one, and examine the distribution of the other x (distance) NO TRANSPORT 3 04/11/2014 OSMOSIS 2. NO WALL t (time) Biophysics I - OSMOSIS x (distance) free DIFFUSION both particles (smaller/larger) reach homogeneous distributions OSMOSIS 3. SPECIAL WALL restricted DIFFUSION: OSMOSIS smaller molecules reach a uniform distribution larger molecules remain in the compartment 4 Biophysics I - OSMOSIS 04/11/2014 OSMOSIS 3. SPECIAL WALL SEMIPERMEABLE – „filter” semi-permeable membrane allows smaller slovent molecules to pass through, but not the larger solute molecules PORE DIAMETER SELECTIVITY animal skin pellicles, walls of living cells, ceramic plate with holes, cellophane OSMOSIS –types of walls, summary type of the wall yes: non-permeable no yes: SEMIPERMEABLE matter transport no free diffusion restricted diffusion: OSMOSIS OSMOSIS: unidirectional matter flow, which takes place by means of diffusion semipermeable wall + concentration difference (from the perspective of osmosis, the dissolved substance’s qualities are irrelevant) 5 Biophysics I - OSMOSIS 04/11/2014 QUANTIFICATION OF OSMOSIS h semisugar solution permeable membrane water J OUT J OUT J IN J IN solvent r: density h: height g = 10 m/s2 solvent + solute mixture semipermeable membrane -solvent flow throught the semipermeable membrane -concetration difference -dynamic equilibrium OSMOTIC EQUILIBRIUM -semipermeable membrane: allows solvent to pass through but not the solute -the volume of the solvent + solute mixture increases HYDROSTATIC PRESSURE (ph) -solvent flow slows down OSMOTIC PRESSURE J OUT J OUT J IN J IN OSMOTIC PRESSURE pressure that has to be exerted on the solution connected to pure solvent by a semipermeable membrane to reach dynamic equilibrium, to counteract osmosis pressure that inhibits the net solvent flow 6 Biophysics I - OSMOSIS 04/11/2014 OSMOTIC PRESSURE VAN’T HOFF’s LAW for dilute solutions and perfect semipermeable membranes using the equation of state of 2. 1. the ideal gas 𝒑osmotic = 𝒄𝑹𝑻 cred V: volume 𝑛𝑟𝑒𝑑 n: mole fraction 𝑅𝑇 p1-p2=posmosis= 𝑉 T: temperature c: concentration R: universal gas constant pV=nRT nblue1=nblue2 p1= 𝑛𝑟𝑒𝑑+𝑛𝑏𝑙𝑢𝑒1 𝑅𝑇 𝑉 p2= 𝑛𝑏𝑙𝑢𝑒2 𝑅𝑇 𝑉 𝒑ozmózis ~𝒄 the osmotic pressure is linearly proportional to the concentration OSMOTIC PRESSURE upon OSMOSIS the net particle transport occurs from the lowconcentration regions (of the solute!!!!!) (low osmotic pressure) to the high-concentration regions (high osmotic pressure) from low osmotic pressure→high osmotic pressure it is always the more dense solution which becomes diluted OSMOSIS 1. 2. solvent solvent + solute mixture 7 Biophysics I - OSMOSIS 04/11/2014 CLASSIFYING SOLUTIONS ON THE BASIS OF OSMOTIC PRESSURE HYPERTONIC ISOTONIC HYPOTONIC higher concentration same concentration lower concentration c > cx c = cx c < cx higher osmotic pressure same osmotic pressure lower osmotic pressure p > px p = px p < px for the cells of the human body, blood: 0.87 % (0.15 M) NaCl physiologic saline solution 3.8 % sodium citrate 5.5 % (0.3 M) glucose x: reference RED BLOOD CELLS IN DIFFERENT ENVIRONMENT HYPERTONIC (more concentrated: 10% NaCl) ISOTONIC (0.87 % NaCl) pout > pin pout = pin net water OUTflux NO net water flux HYPOTONIC (less concentrated: 0.01% NaCl) pout < pin net water INflux 8 Biophysics I - OSMOSIS 04/11/2014 RED BLOOD CELLS IN DIFFERENT ENVIRONMENT HYPOTONIC IZOTONIC HYPERTONIC Role of osmosis in the life of plant cells PLANT CELLS IN DIFFERENT ENVIRONMENT net water OUTflux PLASMOLYSIS plasma membrane is pulled away from the cell wall NO net water flux net water INflux TURGOR PRESSURE plasma membrane is pushed to the cell wall 9 Biophysics I - OSMOSIS 04/11/2014 OSMOSIS IN THE MEDICAL PRACTICE 1. INJECTION, INFUSION drugs are dissolved in physiological saline solution isotonic environment (compared to the body fluid) water outflow 2. TREATMENT OF OEDEMAS, INFLAMED AREAS abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling (fluid accumulation) dextran-solution/bitter salt (MgSO4-solution)-based treatment hypertonic environment is created (compared to the swollen areas) induces water outflow from the swollen areas reduced swelling hypertonic water influx 3. TREATMENT OF CONSTIPATION - LAXATIVE SALTS laxative salts are not absorbed by the large intestine hypertonic environment is created in the large intestine results in water influx into the large intestine dilution of colonic content, facilitated excretion hypertonic OSMOSIS IN THE MEDICAL PRACTICE 4. DIALYSIS different particles can be sorted by semipermeable membranes pore size of the membrane determines which molecules can pass through the membrane dialysis bag semipermeable membrane concentrated solution t=0s t 10 Biophysics I - OSMOSIS 04/11/2014 OSMOSIS IN THE MEDICAL PRACTICE 4.1. HAEMODIALYSIS treatment of patient with severe kidney disease remove soluble chemicals toxic for the body (protein products, toxins, other waste products exit with water, essential plasma proteins, cellular elements of blood remain), Schematic diagram of haemodialysis („artificial kidney” instrument). essential element:long semi-permeable membrane (cellophane), surrounded by dial.solution average treatment time: 4-8 h protein products toxins other waste products dial.solution has to be changed frequently check ion-concentrations and metallic-ioncontaminations in the solution OVERVIEW • Osmosis • Van’t Hoff’s law • Osmotic pressure and its significance (rbc, medical application) 11 Biophysics I - OSMOSIS 04/11/2014 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) 12 Biophysics I - OSMOSIS 04/11/2014 Membrane-models Irving Langmuir was an American chemist and Lipid-soluble substances physicist. 1932 – Nobel enter prize the cell quickly. 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 13 Biophysics I - OSMOSIS 04/11/2014 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 14 Biophysics I - OSMOSIS 04/11/2014 Example 1: DIFFUSION THROUGHT THE CELL MEMBRANE EXTRACELLULAR SPACE MATTER TRANSPORT LIPID BILAYER MEMBRANE PROTEINS water apolar molecules ions monosaccharides amino acids metabolites INTRACELLULAR SPACE cytoplasm 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 15 Biophysics I - OSMOSIS 04/11/2014 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 16 Biophysics I - OSMOSIS 04/11/2014 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 17