Lecture 2 - Cell Membrane - Structure and Function PDF

August 24, 2023 Announcements: 1. I- clicker a. Almost everyone is registered to participate in the i-clicker activities b. Next Tuesday, I will have a practice session to check out the system Will not effect your grade. 2. Lecture 2 – Cell Mem...

August 24, 2023 Announcements: 1. I- clicker a. Almost everyone is registered to participate in the i-clicker activities b. Next Tuesday, I will have a practice session to check out the system Will not effect your grade. 2. Lecture 2 – Cell Membrane – Structure and Function  Lecture 2 Cellular Membranes + Transport of Solutes and Water Reference; B.B. Chap. 2, pgs. 9 – 20; Chap 5, pgs. 102 – 105, 108 – 117, 123-124 I. Cell Membrane A. function 1. compartmentalization a. selective permeability b. membrane translocation systems 2. receptor for cell activity modifiers 3. structural component of cell organelles 4. conduit for information exchange B. composition 1. Davson–Danielli bimolecular leaflet (1956) a. phospholipid bilayer b. absorption of proteins on lipid surface c. termed "unit membrane" 2. lipid bilayer a. amphiphilic phospholipids i. possess polar and non-polar moieties ii. e.g. phosphatidylethanolamine b. phospholipids added to aqueous media i. form surface coat ii. form micelles & bilayers c.phospholipid bilayer characteristics i. ideally suited to separate aqueous compartments ii. impermeable to charged molecules, e.g. Na+, Cl-, K+ iii. permeable to small uncharged (even polar) molecules, e.g. CO2, O2, NH3, H20 iv. degree of H2O permeability varies w. membrane 3. Singer Nicholson fluid-mosaic model (1976) “proteins floating on sea of lipids” a. classification of protein components i. integral – tightly affiliated with bilayer ii. peripheral – easily dissociated from bilayer b. bilayer protein association mechanisms i. integral proteins (a) transmembrane segments i. formed from hydrophobic amino acids ii. most often α-helical protein domains (B) iii. often multipass domains (C) iv. imbedded to one side only (D) ii. peripheral protein (A) (a) nonconvalently bonded with integral proteins (b) usu. globular proteins iii. proteins exhibit lateral mobility, except: (a) when limited by membrane domain boundary (e.g. tight junction) (b) “protein tethering” c. proteins are 1o functional component of membrane (1) translocation (carrier, channel, pore) (2) enzyme (3) ligand binding receptor (4) identity marker (5) adhesion molecule (6) cytoskeletal attachment (7) intracellular signaling participant d. multimeric protein complexes (1) non-covalent membrane protein interactions often form large complexes (2) allow complex transport and signaling functions bb350435.f3.gif.url 4. membrane glycoproteins a. external surface of all eucaryotic cells coated by “glycocalyx” b. oligosaccharide chains link covalently to both phospholipids & proteins c. enormously diverse d. function i. cell identity marker (unique constituency /cell type) ii. cell adhesion, blood clotting, inflammation, etc. II. Fluid Compartments (BB, Chap. 5) A. cell membranes function as body fluid boundaries B. body fluid compartments 1. total body fluid volume = 42 l. a. intracellular fluid = 25 l. b. extracellular fluid = 17 l. i. interstitial volume = 14 l. ii. plasma volume = 3 l. C. cell membranes responsible for constituent gradients 1. principle ion gradients extracellular intracellular a. cations Na+, Ca++ K+, Mg++ b. anions Cl -, HCO3- protein, PO4-3 2. gradients result from membrane function a. selective permeability b. membrane translocation III. Movement of Solute in Solvent A. gas diffusion 1. movement of molecules result of kinetic energy temperature velocity = √ mass 2. molecules have same velocity and random direction if: a. heat content uniform and constant b. identical mass B. diffusion of solute across cell membrane 1. three stage process a. two aqueous phases + cell membrane b. solute flux through lipid >> solute permeability 2. rate α particulate concentration gradient 3. rate independent of solute properties B. osmolality 1. water concentration usu. expressed in terms of solute contained a. unit = osmole b. 1 osmole = one G.M.W. solute particles / kg H2O c. 1 osmole solute decreases sol’n freezing point 1.86o C 2. other colligative properties: a. boiling point (increases) b. vapor pressure (decreases) 3. expressed biologically as milliosmoles, e.g. plasma is 300 mOsm 4. examples: 1 80 g glu co s e = 1 M glucose = 1 Osm glucose 1l 5 8.5 g N a C l = 1 M NaCl = 2 Osm NaCl 1l 9 5 g M gC l 2 = 1 M MgCl2 = 3 Osm MgCl2 1l C. osmotic pressure 1. force exerted on the walls of a container due to osmotic activity  2. described by van’t Hoff equation (1885) π = n R T ∆C where: R = gas constant (0.082 l – atm o K-1 mole-1 ) T = absolute temperature (oK) ∆C = concentration difference (moles) n = # dissociable particles π = osmotic pressure (atm) example: Determine the osmotic pressure that would be produced by a “physiological salt solution” (0.15 M NaCl) across a semipermeable membrane at 37o C π = n R T ∆C = 2 (0.082)(273 + 37)(0.15) = 7.62 atm = 5796 mmHg  2. tonicity a. cell volume is reflection of media concentration b. tonicity expresses effect of media on cell volume 300 mOsm > 300 mOsm < 300 mOsm isotonic hypertonic hypotonic cells shrink - crenation cells swell - lysis c. tonicity and osmolality are not synonymous i. if solute is lipid soluble (e.g. glycerol, urea) ii. 300 mOs/l solution would be hypotonic, causes lysis August 29, 2023 Announcements: 1. Last Thursday: Lecture 1 – body organization and anatomy nomenclature Lecture 2 - cell membrane 2. Complete Lecture 2. V. Membrane Transport of Substrates 3. Begin lecture 3 – Histology 4. I-clicker activity after lecture – no credit, to check out the system Some clarification from last lecture: molality vs molarity molar solution (M) = solute added to flask, volume brought up to 1 liter molal solution (m) = solute + 1000 g of solvent 1 M NaCl = 0.946 m NaCl same relationship of osmolar and osmolal solutions. colligative factors measure osmolality V. membrane translocation (movement of substrate across barrier) A. simple (passive) mechanisms 1. through bilayer (negligable for hydrophilic substances) 2. pore – e.g. aquaporin 3. channel a. gated (voltage, ligand, second-messenger controlled) b. selectivity filter (e.g. sodium, potassium, calcium) B. carrier mediated 1. introduction a. protein carriers specifically bind to one or more solutes b. translocate solute to opposite side of membrane c. classification (i) passive – facilitated diffusion (ii) active – requires energy 2. ping pong model 3. characteristics of carrier mediated transport a. saturation 4. specificity a. each carrier system transports specific substance or grps (1) e.g. amino acids transported by different carrier than glucose (2) membrane carriers are group specific b. specificity not perfect 5. competitive inhibition a. competition occurs between molecules of closely related structure b. example – glucose facilitated diffusion A [A] A&B i TIME A = glucose, B = galactose (if transported by same carrier) 6. non-competitive inhibition a. Solutes compete for carrier attachment b. Only one solute transported c. In presence of inhibitor, rate independent of [substrate] (limited by the few carriers present) A [A] A = glucose i I = phlorizin A+I TIME VI. Classification of Carriers by Number of Solutes Translocated A. uniport – translocation of single substrate across barrier B. coupled transport – simultaneous translocation of 2 or more substrates 1. attachment of one solute increases the affinity of a second 2. classification a. symport – translocation of substrates in same direction b. antiport – transport of substrates in opposite direction 3. examples a. symport b. antiport one of the solutes often driven across membrane by other solute VII. Summary facilitated diffusion passive symport carrier transport coupled transport mediated antiport active VIII. Active Transport A. carrier mediated transport against an electrochemical gradient, requiring expenditure of metabolic energy. B. Na-K ATPase 1. exports 3 Na+ in exchange for 2 K+ 2. requires ATP 3. inhibited by ouabain 4. prolific carrier, present in nearly all cells 5. provides energy for many transport processes C. Na-K pump model 1. ATP bd to enzyme (exposed to ICF) 2. 3 Na+ bind to enzyme 3. ATP hydrolyzed, conformation ∆ (exposed to ECF) 4. Na+ released in ECF 5. & 6. 2 K+ bind to enzyme 7. PO4 leaves, conformation ∆ (exposed to ICF) 8. ATP binds, K+ released into ICF 9. Ouabain binding to Na-K ATPase, prevents K+ binding  2. other active transporters a. Ca+2 ATPase b. H+ ATPase X. Secondary Active Transport A. utilizes established substrate gradients to transport second substrate 1. both symport and antiport classes 2. no direct energy requirement B. example – Na-Ca exchanger + [Na ] [Na+] Na K 2Na Ca [Ca+2] [Ca+2]  Question #1 1. The membrane which lines the external surface of the stomach is correctly termed: a. parietal peritoneum d. visceral pleura b. visceral peritoneum e. parietal pleura c. parietal pericardium Question #2 2. Which of the following solutions is hypotonic? a. 0.30 M urea d. 0.30 M NaCl b. 0.15 M NaCl e. 0.30 M glucose c. 0.10 M MgCl2 Question #3 3. The left elbow is ______ to the left wrist: a. inferior d. dorsal b. distal e. proximal c. contralateral contralateral = opposite side vs. ipsilateral = same side As in “Her joint injuries are ipsilateral.” Question #4 4. The figure above is representative of a _______ section. a. frontal d. sagittal b. coronal e. transverse c. oblique Question #5 π A B O O O O O O O O O O O O O O O O O O 5. The model above represents two closed compartments separated by a semipermeable membrane. The initial concentration of solute in chamber “B” was higher than that of chamber “A”. When equilibrium is reached you would expect: a. [Osm]A = [Osm]B b. [H2O]B > [H2O]A c. [H2O]A = [H2O]B d. stopping pressure = osmotic pressure e. π = 0 mmHg Some clarification from last lecture molality vs molarity molar solution (M) = g of solute in 1 liter H20 ÷ GMW of solute molal solution (m) = g of solute in 1000 g of solution ÷ GMW of solute distilled H20 = 1000 g ÷18 g/M = 55.56 M or m most solutes have higher specific gravity than water, hence, lower molality: for example: 58.5 g NaCl +1000 g H20 = 1 M solution however, a liter of a 1 M solution of NaCl weighs 1058.8 g. Since there is 55.26 g of NaCl /1000g solution ÷ 58.5 g/M = 0.946 m August 21, 2014 Announcements: 1. please see me after class today, if you missed our first meeting 2. first I-clicker session next Tuesday 3. Lecture 2 – Cell Membrane – Structure and Function a. elaboration throughout course b. focus on notes to learn the basics at this time