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BIOL 370
Dinu Nesan

Lecture 2: Ion and Water Balance - The environment: External world “animal”, Extracellular fluid “cell” or Cytoplasm “intracellular enzymes” - Homeostasis: Osmotic regulation, Ionic regulation & Nitrogen regulation - Solvents: The most abundant molecules in a liquid mixture (e.g. Water) - Solute: The other molecule in a liquid o Solutes dissolve in solvents - Osmotic pressure: Force associated with water movement, depends on relative osmolarity on both side of a semipermeable membrane (can predict whether the solution will gain or lose water by osmosis) o Osmolarity: The number of particles in a given volume of solution *dissolved particles+ “OsM” o Hyposmotic: (same for hyperosmotic)  If cell is hyposmotic: it contains less particles than the surrounding  If the solution is hyposmotic: It contains more particles than the cell - Diffusion: The direction of diffusion is dependent on the concentration gradient, not so much for rate - Colligative properties of water: More solute reduces freezing point, increases BP, VP & OP - Tonicity: The effect of a solution on cell volume (depends on membrane permeability) o Hypertonic solution: cell shrinks, water leaves the cell by osmosis o Hypotonic solution: cell swells, water enters the cell by osmosis o Isotonic solution: cell does not shrink nor swell, no net osmosis  The osmolarity of the cell & the solution being the same  The solution is hyperosmotic/hyposmotic, but the membrane is not permeable for the solute - Lipid rafts: Different lipid composition than surrounding plasma membrane o 3-5x cholesterol, increases fluidity & decreases permeability & provides more tightly packed hydrophobic chains of lipids o Rich in sphingolipids that alters electrical properties o More glycolipids that’s responsible for communication between cells - Temperature & Membrane Fluidity o Low temperatures  Membrane solidify, protein movement is impaired o High temperatures disrupts van der Wall’s forces & Hydrogen bonds  Membrane liquefy, the membrane integrity is compromised & this decreases its effectiveness as a barrier - Membrane Proteins (2) o Integral membrane proteins: Tightly bound to the membrane o Peripheral membrane proteins: Weaker associated with the lipid bilayer - Membrane Transporters (3) o Passive diffusion: Lipid-soluble, no transporter, no ATP (Steeper gradient  Faster rate) o Facilitated diffusion: Non-Lipid-soluble, protein transporters required, no ATP (Steeper gradient  Faster rate until saturation)  Ion “gated” channels: Small pores for specific ions  Voltage gated “membrane potential”, ligand gated “chemical msger” or mechanogated  Porins: Similar to ion channels but for bigger molecules  Permeases: Binds substrate  Conformational change  Released intracellularly o Active transport: Non-Lipid-soluble, protein transporters required, ATP needed, molecules can be moved or against concentration gradient  Primary “Direct”: Energy from ATP hydrolysis (ATPases) + + 2+  P-type: pump specific ions (e.g. +a , K , Ca )  F-type & V-type: Pumps proton (H )  ABC type: Carry larger organic molecules (e.g. Toxins)  Secondary “Coupled”: Energy in electrochemical gradient of 1 molecule drives another molecule against its gradient  Exchangers “Antiporters”: Molecules move in opposite directions  Cotransporters “Symporters”: Molecules move in the same direction Lecture 3: Ionic Regulation - Electrical gradients: Some transport processes affect electrical gradients in-addition to chemical gradient o Electroneutral carriers: Transfers uncharged molecules or Equal # of particles with the same charge (e.g. Na /H exchanger) + + + + o Electrogenic carriers: Transfers Charge (E.g. Na /K ATPase – 3Na for 2K ) - Membrane potential: The difference in charge inside & outside of the cell membrane o Provides energy for transport & cell-to-cell signalling + + - o Most dependent upon Na , K & Cl o Changes in membrane permeability changes the membrane potential  Depolarization: Cell becomes more positive on the inside  Hyperpolarization: Cell becomes more negative on the inside - Equilibrium potential: Each ion’s own equilibrium potential, calculated with Nernst equation o Ion diffuses down its concentration gradient until it reaches its electrochemical equilibrium o Depends on membrane permeability o Goldman’s equation: Accounts for permeability & multiple ions - Ionic Regulation (2 strategies) o Ionoconformer: Internal ion concentration same as external o Ionoregulator: Controls internal ion concentration - Osmotic Regulation (2 strategies) o Osmoconformer: Internal osmolarity similar to external o Osmoregulator: Controls internal osmolarity - Ability to cope with external salinities o Stenohaline: Tolerate only a narrow range within osmolarity o Euryhaline: Tolerate wide ranges of osmolarities (ATP expensive) - Sources of H 2 & Solutes (3 sources) o Dietary water: Water ingested (stored within plants or animal tissues) o Metabolic water: Water generated via oxidative phosphorylation (H O pr2duction via hydrolysis) o Drinking  E
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