OSMOSIS. BIOPHYSICS I October 25. Beáta Bugyi University of Pécs, Medical School, Department of Biophysics,

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1 BIOPHYSICS I October 25. Beáta Bugyi University of Pécs, Medical School, Department of Biophysics,

2 Overview 1. Diffusion brief overview 2. Osmosis: molecular basis and quatification 3. Medical & biological importance of diffusion and osmosis

3 Diffusion - summary GENERAL DESCRIPTION OF TRANSPORT PROCESSES ONSANGER S LINEAR EQUATION linear, irreversible processes Interaction flow density of the extensive quantity (J) is linearly proportional to the gradient of the corresponding intensive quantity (X) J LX DIFFUSION determined by the inhomogenous distribution of particles gradient of the intensive quantity: concentration (c), chemical potential (μ) caused by the random thermal motion of particles net transport of particles from a region of higher concentration to a region of lower concentration by random molecular motion continues until the distribution of particles is uniform

4 Diffusion - summary FICK s I. LAW spatial description in1d J c D x FICK s II. LAW spatiotemporal description in 1D c ( ) x c D x t [ D] m s 2 D: DIFFUSION COEFFICIENT the amount of substance that diffuses through a surface unit during a time unit if the concentration drop was unity D kt 6 r spherical particle temperature (T) mass, geometry (M, r) viscosity of the medium (η) D m 2 /s

5 Osmosis: phenomenon

6 Osmosis molecular basis 1. SOLID (nonpermeable) WALL NO TRANSPORT the distribution of particles does not change

7 Osmosis molecular basis 2. NO WALL free DIFFUSION both particles (smaller/larger) reach equal distributions

8 Osmosis molecular basis 3. SPECIAL WALL: SEMIPERMEABLE semipermeable wall allows smaller slovent molecules to pass through, but not the larger solute molecules filter pl: animal skin pellicles, walls of living cells, ceramic plate with holes, cellophane restricted DIFFUSION smaller molecules reach a uniform distribution larger molecules remain in the compartment

9 Osmosis type of the wall yes nonpermeable no yes semipermeable matter transport NO free DIFFUSION restricted diffusion : unidirectional matter flow, which takes place by means of diffusion

10 Osmosis - quantification low solute high solute water solvent solute semipermeable membrane concentration difference + semipermeable membrane

11 Osmosis - quantification low solute J IN high solute J OUT water solvent solute semipermeable membrane concentration difference + semipermeable membrane solvent (water) flows through the semipermeable membrane J IN J OUT

12 Osmosis - quantification low solute J IN high solute J OUT h water solvent solute semipermeable membrane concentration difference + semipermeable membrane solvent (water) flows through the semipermeable membrane JIN J OUT the volume of the more concentrated solution increases (height of the liquid column: h)

13 Osmosis - quantification low solute J IN high solute J IN J OUT J OUT h water solvent solute semipermeable membrane concentration difference + semipermeable membrane solvent (water) flows through the semipermeable membrane JIN J OUT the volume of the more concentrated solution increases (height of the liquid column: h) the pressure increases in the more concentrated solution: hydrostatic pressure, h dynamic equilibrium: for solvent flow OSMOTIC EQUILIBRIUM JIN J OUT

14 Osmosis osmotic pressure low solute J IN high solute J IN J OUT J OUT h water solvent solute semipermeable membrane 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 p osmotic gh : density h: height of the liquid column g = 10 m/s 2

15 Osmotic pressure for diluted solutions and perfect semipermeable membranes using the equation of state of the ideal gas p p osmosis osmosis V n V p osmosis crt nrt RT VAN T HOFF s- LAW the osmotic pressure exerted by any substance in dilute solution is the same as that it would exert if present as gas in the same volume

16 Classifying solutions on the basis of osmotic pressure ISOTONIC same osmotic pressure extra- and intracellular solutions with the same osmotic pressure the osmotic pressure of the solutions in the cells of human body = osmotic pressure of a 0,87 % (n/n) (0.15 M) NaCl solution physiologic saline solution HYPERTONIC higher osmotic pressure extracellular solution has higher osmotic pressure than the intracellular solution water efflux HYPOTONIC lower osmotic pressure extracellullar solution has lower osmotic pressure than the intracellular solution water influx

17 Red blood cells in different environment mammalian cells: p 5 atm 10 Pa p 6 ozmotic Pa HYPERTONIC (more concentrated: 10% NaCl) ISOTONIC (0.9 % NaCl) HYPOTONIC (less concentrated: 0.01% NaCl) passive water efflux passive water influx

18 Red blood cells in different environment HYPERTONIC ISOTONIC (0.9 % NaCl) HYPOTONIC

19 Plant cells in different environment plant cells: p 6 osmotic Pa HYPERTONIC ISOTONIC HYPOTONIC PLAZMOLYSIS plasma membrane pulls away from the cell wall TURGOR PRESSURE plasma membrane pushed to the cell wall (turgor pressure)

20 Osmosis in the medical practice injection, infusion physiologic saline solution oedemas, inflamed areas dextran-solution / bitter salt (MgSO 4 -solution): hypertonic compared to the fluids of the body water efflux laxative salts barely absorbed by the large intestine, thus they create hypertonic conditions which causes water influx into the large intestine dilution of colonic content, facilitate excretion

21 Dialysis different (macro)molecules are sorted by semipermeable membranes pore size of the membrane the limit in molecular mass of which molecules can pass through the membrane dialysis bag semipermeable membrane concentrated solution t = 0 s t

22 Haemodialysis remove soluble chemicals toxic for the body protein products toxins other waste products

23 Semipermeable membranes wall of living cells: cell membrane

24 Transport across cell membranes without transporter molecule TRANSPORT MECHANISM with transporter molecule diffusion facilitated diffusion channel carrier-protein carrier-protein passive transport ENERGETIC REQUIREMENTS active transport

25 Transport across cell membranes Passive transport: DIFFUSION the particle transport is determined by the concentration gradient transporter : no energetic requirement: no rate is determined by concentration gradient temperature size and shape of the diffusing particel size of the surfacefelület méretétől distance hydrophobic molecules: O2, N2 small polar molecules: CO2, water, alcohol, urea, glycerine glucose, saccharose

26 Transport across cell membranes Passive transport: FACILITATED DIFFUSION THROUGH ION CHANNELS the particle transport is determined by the concentration- and electric potential gradient electrochemical potential gradient transpoter : ion channel: transmembrane proteins (pore) closed state: no transport open state: transport regulation of the open/closed transition: mechanosensitive (mechanical effect) potential difference (potential difference between the membrane, see action potential) ligand-driven (ligand bound to the receptor) selectivity: charge and size of the ion energetic requirement: no

27 Transport across cell membranes Passive transport: FACILITATED DIFFUSION CARRIER PROTEINS the particle transport is determined by the concentration gradient transpoter : carrier-proteins (mediator, transporter) specifically bind the ions or molecules and promote their transport transport: reversible conformational change in the carrier-protein energetic requirement: no

28 Transport across cell membranes Active transport: FACILITATED DIFFUSION CARRIER PROTEINS the particle transport is determined by the concentration gradient transpoter : carrier-proteins (mediator, transporter) specifically bind the ions or molecules and promote their transport transport: reversible conformational change in the carrier-protein energetic requirement: yes