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UNCG KIN 292 - Active Transport

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KIN 292 1st Edition Lecture 10Outline of Last Lecture I. 4.5 Osmosis: Passive Transport of Water Acroos MembranesOutline of Current Lecture I. 4.4 Active TransportCurrent Lecture4.4 Active Transport- Nonspontaneous - actively transported substance moves uphill, which requires cell energy - Involves integral membrane protein that spans membrane - Affinity of transporter’s binding site for its solute is greater when the binding site is exposed to one side of membrane compared to the other - Demonstrates saturation - Active energy moves substances against their concentration gradient which is why it requires energyActive transport across a membrane and impact of binding affinityTypes of Active TransportThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Primary active transport o Uses energy from ATP hydrolysis in most cases o Functions as transporter and enzyme o Termed “pump” or ATPase because of energy source - Secondary active transport o Energy released from passive transport of one substance down its gradient is used to drive the flow of another substance up its gradient. Can be compared with coupled enzyme reactions discussed earlier o Actively transported substance may go in same or opposite direction as passively transported substancePrimary active transport by the Na+/ K+ pump or Na+/ K+ ATPase. Has high and specific affinity for Na+ on inside where [Na+] is low and low affinity for Na+ on outside where [Na+] is high, vice versa for K+Sodium higher on the outsidePotassium higher on the insideSecondary active transport. Cotransport or Countertransport(a) Sodium-linked glucose transport. Example of Cotransport – substances move in same direction. Also called symport. Sym- Greek for with or together Diffusion of Na+ provides energy so that glucose can be actively transported (b) Sodium-linked proton transport. Example of Countertransport – substances move in opposite direction. Also called uniporters or exchangers Diffusion of Na+ provides energy so that H+ can be actively transported. Na+ diffusion provides energy for several secondary active transport proteinsActive–Passive Coordinationo Ions “leak” through membranes down their gradients and active transport is used to return them to their proper location. Important tidbit - Although ions are considered impermeable, if enough force is provided some will be pushed through the nonpolar lipid bilayer. Also the case for H2O. o Active transport keep the intracellular and extracellular fluid separateo ICF/ECF concentrations differ because of active transport.Pumps and leaks in a cell. An important exampleNa+ leaks in and K+ leaks out down their respective huge concentration gradients, which provide a big push for both (lots of potential energy). The Na+/K+ pump stays very busy tomaintain the proper concentration required for them to be at equilibrium (Equilibrium potential). How busy?The Na+/K+ pump accounts for about 1/5 of the total energy used in most non-neuron cells. It accounts for about 2/3 of the total energy used by nerve cellsIn perspective, if there are 2,200 kcals in body, 700 are going towards sodium potassium pumpChap 4.5 Osmosis and Tonicityo Osmosis - One Definition: an ability to learn and understand things gradually without much effort o Does not apply to learning physiology because it is an active process – not passive o Tonicity – one Definition: The sustained partial contraction of resting or relaxed muscles o Osmosis and tonicity for our purposes deal with movement of water across cell membranes4.6 Transport of Material Within Membrane-BoundCompartmentso Transport of macromolecules o Uses membrane compartmentso Endocytosis o Secretory vesicles o ExocytosisThe Three Types of Endocytosis (a) Particle is surrounded by the membrane then it breaks away (Phagosome) and fuses with a lysosome (Phagolyosome). Popular way for WBC’s to remove foreign bodies and bacteria. (b) Solutes enter an indentation in the membrane, which then breaks away (Endosome). Nonspecific process used by most cells to bring in largemolecules (c) Similar to (b), but is specific. Receptor proteins recognize specific particles and escorts them to areas where endocytosis will occur forming a coated vesicle. The vesicle fuses with a lysosome (Endolysosome) and the particles are degraded (similar to (a)).Receptor- lock- and-key model, only binds to specific membraneProteins can move in the membrane4.7 Transport Across Epitheliumo The processes of absorption (external environment to internal) and secretion (internal to external) requires transport across entire cell o Involves two membranes. Our discussion to this point has focused on transport betweentwo internal fluid compartments, which involves only one membraneFigure 4.25 Epithelial water transport in an epithelium that absorbs water and solutes.o Solutes areactivelypumped intothe interstitialfluido Osmoticpressure of theinterstitial fluidincreaseso Water isosmotically pulled across the cell and transported from the lumen to the interstitial fluido Affects the osmotic pressure, change in concentration means pulling water out. Osmosis is a passive processo Have to go through ions to change concentration from what it was to try to get water to flow in Clinical Connections 4.1 Cystic Fibrosis. The most common hereditary disease among Caucasians. Caused by defect in respiratory epitheliumAirway passages leading to lungs become clogged with mucus leading to much, vigorous coughing. Breathing is difficult and pneumonia is common because bacteria that thrive in the mucus cannot be easily removed. No cure. Average life span is about 50 years.Normal solute and water transport Chloride is actively transported from interstitial fluid to airway lumen. This creates a negative electrical gradient driving the passive flow of sodium in same direction and raising osmotic pressure on lumen side. Water is then passively secreted down osmotic gradient and dilutes the mucus making it easier to clear from the airways.Defective solute and water transport in cysticfibrosisA defect in the chloride channel protein directly impedes Cl- transport, which indirectly impedes Na+ transport. As a result, the epithelium cannot produce the osmotic gradient necessary for water secretion. Water transportoccurs secondary to solute


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