Chapter 5 Membrane Dynamics, Part 2

Chapter 5 Membrane Dynamics, Part 2 - Ch 5: Membrane...

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Unformatted text preview: Ch 5: Membrane Dynamics, Part 2 Ch Cell membrane structures and functions Membranes form fluid body compartments Membranes as barriers and gatekeepers How products move across membranes i.e., methods of transport Vesicular Transepithelial Osmosis Distribution of water and solutes in cells & the body Chemical and electrical imbalances Resting Membrane Potential Membrane permeability and changes Membrane Dynamics, Part 1 Review Review Law of Mass Balance Ins = outs Diffusion Too slow for many processes Facilitated Diffusion Carrier proteins Protein-mediated Transport Very selective Active Transport uses ATP Na+ - K+ ATPase pump Vesicular Transport Vesicular Movement of macromolecules across cell Movement macromolecules membrane: membrane: 1. Phagocytosis (specialized cells only) 2. Endocytosis Pinocytosis Receptor mediated endocytosis (Caveolae) Potocytosis 1. Exocytosis 1. Phagocytosis 1. Requires energy Requires Cell engulfs particle into vesicle via pseudopod pseudopod formation formation E.g.: some WBCs engulf bacteria engulf Vesicles formed are much Vesicles larger than those formed by endocytosis endocytosis Phagosome fuses with Phagosome lysosomes ⇒ ? (see Fig. 5-23) (see 2. Endocytosis 2. Requires energy Requires No pseudopodia - Membrane surface indents indents Smaller vesicles Nonselective: Pinocytosis for fluids & dissolved substances dissolved Selective: Receptor Mediated Endocytosis via clathrinvia coated pits - Example: LDL cholesterol and Familial Hypercholesterolemia Potocytosis via caveolae Fig 5-24 Receptor Mediated Endocytosis and Membrane Recycling Membrane Fig 5-28 3. Exocytosis 3. •Intracellular vesicle fuses with membrane → Intracellular •Requires energy (ATP) and Ca2+ •Uses: •large lipophobic molecule secretion; • receptor insertion; •waste removal Movement through Epithelia: Transepithelial Transport Transepithelial Uses combination of active and passive transport Molecule must Molecule cross two phospholipid bilayers bilayers Apical and basolateral cell membranes have different Apical proteins: proteins Na+- glucose transporter on apical membrane Na+/K+-ATPase only on basolateral membrane Fig 5-26 Transepithelial Transport of Glucose Transepithelial 1. Na+/Glucose symporter only found on apical side 2. Na+/K+-ATPase only found on basolateral side 3. Facilitated diffusion Transcytosis Transcytosis Endocytosis → vesicular transport → Endocytosis exocytosis Moves large proteins intact Moves Examples: Examples: Absorption of maternal antibodies from antibodies breast milk Movement of proteins Movement across capillary endothelium endothelium Distribution of Solutes in Body Distribution Depends on selective permeability of cell membrane transport mechanisms available Water is in osmotic equilibrium (free Water movement across membranes) movement Ions and most solutes are in chemical Ions disequilibrium (e.g., Na-K ATPase Pump) disequilibrium Electrical disequilibrium between ECF and Electrical ICF ICF Fig 5-33 Distribution of Solutes in Body Fluid Compartments Distribution Compare to Fig 5-33 Osmosis Osmosis Compare to Fig. 5-29 Movement of water down its concentration gradient. Opposes Osmotic movement Osmotic of water pressure across pressure membrane Water moves freely in body until osmotic equilibrium is reached equilibrium Molarity vs. Osmolarity Molarity In chemistry: Mole / L Avogadro’s # / L In Physiology Important is not # of Important molecules / L but molecules # of particles / L: osmol/L or of OsM OsM Why? Osmolarity takes into account dissociation (solubility) of molecules in solution Osmolality = OsM/Kg of sol’n Convert Molarity to Osmolarity Convert Osmolarity = # of particles / L of solution 1 M glucose = 1 OsM glucose 1 M NaCl = 2 OsM NaCl 1 M MgCl2 = 3 OsM MgCl2 Osmolarity of human body ~ 300 mOsM Compare isosmotic, hyperosmotic, hyposmotic (p Compare 156) 156) Tonicity Tonicity Physiological term describing how Physiological cell volume changes if cell placed in the solution the Always comparative. Has no units. Isotonic sol’n = No change in cell Hypertonic sol’n = cell shrinks Hypotonic = cell expands Depends not just on osmolarity but on nature of solutes and permeability of membrane of Penetrating vs. Nonpenetrating Solutes Solutes Penetrating solute: can enter cell Penetrating (glucose, urea) (glucose, Nonpenetrating solutes: cannot enter Nonpenetrating cell (sucrose, NaCl*) cell Determine relative conc. of Determine nonpenetrating solutes in solution and in cell to determine tonicity. in Water will move to dilute nonpenetrating solutes Penetrating solutes will distribute to equilibrium Fig 5-30 Osmolarity and Tonicity Comparison Osmolarity A is isosmotic to B Compare to Fig 5-35 A is hypotonic to B IV Fluid Therapy IV 2 different purposes: Get fluid into dehydrated cells or Keep fluid in extra-cellular compartment Electrical Disequilibrium and Resting Membrane Potential (pp.156-163) will be covered at the beginning of Ch 8 Which of the following is a way for solutes in a aqueous solution to move from an area of high solute concentration to an area of low solute concentration? concentration? A. B. C. D. E. Facilitated diffusion Osmosis Active transport A and B None of these Which of the following defines the term specificity? term A. movement of molecules by the use of vesicles B. the energy required to move molecules C. a group of carrier proteins operating at their maximum rate D. carrier transport of a group of closely related molecules E. none of these Water will always move from ___________ situations to _______ situations. situations A. B. C. D. Hyperosmotic, hyposmotic Hyposmotic, hyperosmotic Hyposmotic, isosmotic Hyperosmotic, isosmotic Which of the following pairs of molecular characteristics favors diffusion through the cell membrane? cell A. B. C. D. Large, polar Large, non-polar Small, polar Small, non-polar Which of the following is a way for solutes in a aqueous solution to move from an area of high solute concentration to an area of low solute concentration? concentration? A. B. C. D. E. Facilitated diffusion Osmosis Active transport A and B None of these ...
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