KIN 292 1st Edition Lecture 10 Outline of Last Lecture I 4 5 Osmosis Passive Transport of Water Acroos Membranes Outline of Current Lecture I 4 4 Active Transport Current Lecture 4 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 energy Active transport across a membrane and impact of binding affinity Types of Active Transport These 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 substance Primary 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 outside Potassium higher on the inside Secondary 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 proteins Active Passive Coordination o 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 separate o ICF ECF concentrations differ because of active transport Pumps and leaks in a cell An important example Na 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 to maintain 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 cells In perspective if there are 2 200 kcals in body 700 are going towards sodium potassium pump Chap 4 5 Osmosis and Tonicity o 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 membranes 4 6 Transport of Material Within Membrane BoundCompartments o Transport of macromolecules o Uses membrane compartments o Endocytosis o Secretory vesicles o Exocytosis The 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 large molecules 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 membrane Proteins can move in the membrane 4 7 Transport Across Epithelium o 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 between two internal fluid compartments which involves only one membrane Figure 4 25 Epithelial water transport in an epithelium that absorbs water and solutes o Solutes are o o o o actively pumped into the interstitial fluid Osmotic pressure of the interstitial fluid increases Water is osmotically pulled across the cell and transported from the lumen to the interstitial fluid Affects the osmotic pressure change in concentration means pulling water out Osmosis is a passive process 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 epithelium Airway 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 transport occurs secondary to solute transport