Week 1 - Class Notes - Jan 8

Week 1 - Class Notes - Jan 8 - Membrane Dynamics: Physical...

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Unformatted text preview: Membrane Dynamics: Physical properties of particles in solution 1) Diffusion 1) – The random movement of molecules down a The down concentration gradient concentration – ends when equilibrium (concentration is equal) ends is achieved is Fig. 3-15, Martini “equilibrium” 2) Flux 2) – the movement of particles across a permeable the membrane in a unit period of time membrane – net flux is zero at equilibrium “net flux” time “equilibrium” • Factors affecting particle diffusion rate across Factors cell membranes: cell – Size (magnitude) of concentration gradient of • larger the gradient, the greater the rate of flux – Permeability of the membrane to substances of • greater the permeability, the greater the rate of flux – Surface area of the membrane across which diffusion is taking place diffusion • larger the area, the greater the rate of flux – Distance across which diffusion must take place across • increase in distance, a decrease in the rate of flux – Molecular weight of the substance of • larger the molecule, a decrease in the rate of flux How do solute particles cross a membrane ? How 1) Simple diffusion of solute particles directly 1) Simple through the lipid bilayer through the – a solute particle will pass directly through if it is: • • • lipid soluble non-polar hydrophobic How do solute particles cross a membrane ? How 2) Simple diffusion of solutes through ion Simple diffusion channels channels – ‘pore’ in the membrane • solute particles pass through a pore down it’s solute down concentration gradient concentration – channels selective for specific cations or anions • Na+, K+, Ca++, Cl- Fig. 3-16, Martini How do solute particles cross a membrane ? How 3) Carrier-mediated diffusion 3) -facilitated diffusion (runs on concentration gradient alone) concentration -primary active transport -secondary active transport 3) Carrier-mediated diffusion 3) Carrier-mediated a) ‘Facilitated’ diffusion (only one to run on Facilitated’ Concentration gradient) • rate of facilitated diffusion depends on: of – solute concentration gradient – affinity for solute on site of transport protein – number of transporter proteins in membrane – rate of conformational change Fig. 3-19, Martini 3) carrier-mediated diffusion carrier-mediated a) primary active transport primary • • transports a molecule against it’s concentration gradient transports against ATP required to provide energy for transport protein ATP required – phosphorylates the carrier protein – phosphorylation causes a conformational change of phosphorylation transport protein transport • Example: Na+/K+ ATPase pump • Fig. 3-20, Martini High [Na+] Low [K+] low [Na+] high [K+] Primary active transport, Figure 3-20, Martini 3) carrier-mediated diffusion carrier-mediated c) secondary active transport (‘symporter’) c) secondary – transport mechanism DOES NOT NEED direct energy transport source (relies on concentration gradient of ONE solute to move the other solute across its concentration gradient.) gradient.) – specific carrier molecules can transport a solute against specific can it’s concentration gradient it’s – uses the potential energy generated by the concentration uses gradient of one solute to drive the transport of a second solute against it’s concentration gradient in the same direction Na /glucose ‘symporter’ Example: Example: Secondary active transport: Na+/glucose symporter Na 3Na+ 2K+ Na+/K+ ATPase pump Na+ 3 Na+ glucose glucose Gut “lumen” Blood stream Intestinal epithelial cell “trans-epithelial” transport of Na 2K d) Secondary active transport (‘ANTIporter’) d) – one solute moves out of cell while another solute moves one into the cell into – concentration gradient of one solute creates the potential concentration energy that causes transport of the second solute against it’s own concentration gradient it’s Na /Ca antiporter 3Na+ 2K+ Na+/K+ ATPase pump Na+ Ca++ Ca++ Osmolarity Osmolarity • Total molar concentration of ALL solution particles ALL – solutes ‘hydrate’ as 1 particle or ‘ionize’ into several solutes particles particles • 0.15 M NaCl = 0.15 M Na+ + 0.15 M Cl- = 0.3 Osm 0.15 Osm – osmolarity of intracellular fluid (ICF) is 300 mOsm osmolarity (0.3 Osm) (0.3 – relative to the ICF (intracellular fluid), the ECF relative (intracellular (extracellular fluid) is: (extracellular • • • iso-osmotic if equal to 300 mOsm iso-osmotic equal hyper-osmotic if greater than 300 mOsm hyper-osmotic greater hypo-osmotic if less than 300 mOsm • solutes • “particles” in water • Na+, Cl-, glucose, urea, NH4+, Mg++, Ca+ +,proteins, organelles – “penetrating” solute • particle dissolved in water that CAN pass particle CAN directly through the lipid bilayer directly urea, NH OSMOSIS OSMOSIS • “the diffusion of water through a semi-permeable the diffusion membrane from a region of low concentration of membrane non-penetrating particles to a region of higher concentration of non-penetrating particles” concentration • Directionality, reason for, and conditions must Directionality, be within the definition when creating your own. be • The concentration to water is inverse to solute The concentration time Fig. 3-17, Martini • OSMOSTIC pressure OSMOSTIC – force caused by water moving into a solution as a force result of higher solute concentration. result • HYDROSTATIC pressure – fluid pressure that counteracts osmotic pressure TONICITY TONICITY • “property of a solution that prevents or promotes prevents osmosis across a semi-permeable membrane” osmosis • refers to the ECF solute concentration relative to the refers ECF ICF solute concentration solute • “predicts” how a cell will behave when suspended in predicts” will a solution solution • hypo-tonic solution – intracellular compartment always gains water, intracellular cell swells and bursts cell – RBC bursts = “hemolysis” • iso-tonic solution – intracellular compartment will not experience a intracellular net gain or loss of water net – RBC maintains “biconcave” shape • hyper-tonic solution – intracellular compartment always losses water intracellular and shrinks and – RBC crenates = “round and rough” • Fig. 3-18, Martini How to determine solution How tonicity 1) FIRST determine the osmolarity of solution 1) without knowing osmolarity, the tonicity of a without solution CANNOT be predicted. CANNOT How do we determine the osmolarity of a How solution? solution? – Count the particles Osmolarity determination Osmolarity 1. Does the solution contain a compound that ionizes? 2. 0.15 M NaCl molar concentration of all= 0.3 Osm NaCl Determine = 0.15 M Na + 0.15 M Cl ll particles Determine a 0.15 Determination of solution Determination tonicity 1) determine the OSMOLARITY of solution 1) 1) determine whether solutes are penetrating or nonpenetrating penetrating lipid soluble solute = penetrating solute lipid 1) Is there a gradient of non-penetrating particles? non-penetrating Is 2) Will osmosis occur? Which direction? 1) Water flowing out of cell: hypertonic 2) Water flowing into cell: hypotonic To be isotonic, a solution must be iso-osmotic and consist To isotonic solution must of effectively non-penetrating particles (solutes) effectively non-penetrating Determination of solution tonicity Determine osmolarity of solution (ECF) Iso-osmotic (= 300 mOsm) Hyperosmotic (>300 mOsm) Solute penetrating? Hypo-osmotic (<300 mOsm) Solute penetrating? YES Hypo-tonic NO Iso-tonic NO Hyper-tonic YES Hypo-tonic Sample problem #1 Sample 300 mOsm (ICF) ECF ECF = 0.15 M NaCl ECF contains: 0.15 M Na+ 0.15 M Cl- 1) ECF Concentration of all solutes = 0.3 M Osmolarity =0.3 Osm (or 300 mOsm) The ECF is ISO-osmotic relative to the ICF The ISO 1) NaCl is a non-penetrating solute NaCl non-penetrating 2) IS there a gradient of non-penetrating particles? IS non-penetrating NO 1) Will osmosis occur? No gradient, so osmosis DOES NOT OCCUR Solution is ISO-tonic Solution ISO Sample problem #2 Sample 300 mOsm (ICF) ECF ECF = 0.3 M Urea ECF contains: 0.3 M urea 1) ECF Concentration of all solutes = 0.3 M Osmolarity = 0.3 Osm (or 300 mOsm) The ECF is ISO-osmotic relative to the ICF 1) Urea is a penetrating solute Urea penetrating 2) Is there a gradient of non-penetrating(NPP) particles? Is non-penetrating(NPP) Yes, because all ECF particles are penetrating. Yes, all 1) Will osmosis occur? Yes, osmosis occurs as the cell gains solute particles, Yes, cell gains water (lysis normally occurs) cell Solution is HYPO-tonic Solution HYPO Sample problem #3 Sample 300 mOsm (ICF) ECF ECF =distilled water ECF contains: 0 M solutes 1) ECF Concentration of all solutes = 0 M Osmolarity = __0 Osm (or 0_ mOsm) The ECF is _hypo_-osmotic relative to the ICF The _hypo_1) There are no ECF solutes. There no 2) IS there a gradient of non-penetrating particles? ____yes, as no particles are in the ecf_________ 1) Will osmosis occur? Yes, water will diffuse from _ecf_____ to the _icf__ Solution is _hypo_-tonic Solution _hypo_ Sample problem #4 Sample ECF = .2 M NaCl ECF .2 300 mOsm ECF contains: (ICF) 0.2 M Na+ ECF 0.2 M Cl1) ECF Concentration of all solutes = _.4__ M Osmolarity = .4__ Osm (or _400__ mOsm) The ECF is _hyper__-osmotic relative to the ICF The _hyper__ 1) Na and Cl are BOTH non-penetrating solutes Na non-penetrating 2) IS there a gradient of non-penetrating particles? Yes, there are more in the ECF 1) Will osmosis occur? Yes, water will diffuse from _icf__ to the ___ecf__ Solution is ____hyper_-tonic Solution ____hyper_ ...
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This note was uploaded on 05/29/2011 for the course BMS 290 taught by Professor Tba during the Spring '08 term at Grand Valley State University.

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