KIN 292 1st Edition Lecture 9These are the notes from Professor Starnes’ lecture of Clinical Human Physiology. These come from the slideshows provided by the professor and include extra notes and explanations. Highlighted or bolded information are things that I believe to be information that is important to look over multiple times. The notes in red are my personal additions and quotes of Professor Starnes from the class lecture. Chapter 4 Cell Membrane Transport Outline of Last Lecture I. 4.1 Factors Affecting the Direction of Transport II. 4.2 Rate of Transport III. 4.3 Passive TransportOutline of Current Lecture I. 4.5 Osmosis: Passive Transport of Current LectureRecap: Membranes Are SelectiveSelectively permeable - Permeable = allow molecules to pass through - Selective = restrictive - Membranes allow the transport of some substances, but not others - Coordinated movement of substances across membranes (or preventing movement as the case may be) is crucial for physiological function of all cells and organs Nonpolar molecules o Easily transported across membrane o Examples: O2, CO2, fatty acids o Soluble and permeable in fatsIons and polar molecules o Normally not transported o Need help to cross nonpolar lipid bilayer o Examples: Glucose, proteins, Na+ 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.Factors Affecting the Direction of Transport: Passive vs Active - think exergonic and endogonic reactions Passive Transport o Spontaneous – Driving force is to decrease difference between sides. Like the mechanical box. Potential energy comes from difference between sides for concentration, electrical charge, or both o Active Transport o Not spontaneous – moves to increase difference o Requires input of energy – Examples – ATP, NADH for electron transport chain to pump H+ across inner mitochondrial membraneFigure 4.1 Chemical driving forces. Concentration difference or gradient (∆C) provides potential energy that can "push" particles from higher to lower concentration areaso o Lipid bilayer is freely permeable to non-polar molecules. o Simple diffusion – movement depends only on concentration. o Polar molecules are not freely permeable and require ∆C and specialized proteins embedded in the membrane to get through (described later) Electrical Driving Force- Membrane potential (Vm) o Is a force Caused by unequal distribution of anions (negatively (-) charged ion) and cations (positively (+) charged ion) across the cell membrane o Magnitude of driving force depends on magnitude of charge separation = source of energy - Principles o Opposite charges attract and Like charges repelFigure 4.2 Electrical driving force caused by unequal distribution of anions (negatively (-) charged ion) and cations (positively (+) charged ion) across the cell membrane.- Note that excess charges on either side tend to cluster near the membrane - Simple Principle: Opposite charges attract and Like charges repelFigure 4.4 Magnitude of electrical driving force is determined by Membrane Potential (Vm) andvalence.- Vm is the magnitude of the charge difference between inside (ICF) and outside (ECF) ofcell. Measured in millivolts. Has a polarity (reference is ICF) - Note that the driving force for the divalent cation in c is the same as for the monovalent cation in b although the voltageacross the membrane is only half as much. - Valence - The number of electrons in an atom's outermost shell. Determines amount of charge on the particle and governs bonding behavior (Chem Review, p.22) Electrochemical Driving Force- Total force acting on particles - Sum of chemical and electrical forces- If chemical and electrical forces act in the same direction: o Electrochemical force acts in the direction of each force o Magnitude = sum of the chemical force and the electrical force o Example: mitochondria’s electrochemical gradient – also called its membranepotential - If chemical and electrical forces act in opposite directions: o Electrochemical force acts in the direction of the stronger force o Magnitude = larger force minus smaller force - Question: If a chemical gradient existed, under which conditions would a particle notbe transported across a membrane even if it is permeable to that particle?- Answer: When the electrical force is equal to, but opposite in direction to, the chemical force Equilibrium Potential (Ex) where x represents chemical symbol for a specific ion. Potassium (K+) shown below- The value for the Membrane potential (Vm) when Electrical force is equal and opposite to the chemical force resulting in an electrochemical force of zero. - (EK = Vm) and No net movement of the ion potassium.- At equilibrium concentration in intracellular and extracellular is not equal. - Equilibrium potential is set and never changes- Membrane potential changes What happens when Vm is not equal to Ex?•If Vm< Ex: E force ↓ and EC force is in direction of C force, which is the force with the greatest magnitude (panel b)•If Vm> Ex: E force ↑ and EC force is in direction of E force What happens when Vm is not equal to Ex?•In simple passive diffusion situations, ions move in the direction of the EC force to attemptto return to Ex. In Vm< Ex (left) K+ moves outward to attempt to restore E force•Does this sound similar to near-equilibrium enzymes? Ex compared to Equilibrium Constant (K)•In simple passive diffusion situations, ions move in the direction of the electrochemical force force to attempt to return to Ex. •For reactions catalyzed by near-equilibrium enzymes, molecules move in the direction of the equilibrium constant (mass action) to attempt to return to K Toolbox: Eqilibrium Potential and the Nernst EquationE(I)- 61mV I o__________ Log _____Z I i•Computation of El: Nernst equation where•El = equilibrium potential of ion l. Note book switches from Ex to El •Z = valence of ion l •[I]o = ECF concentration of ion l at steady state •[I]i = ICF concentration of ion l at steady state Toolbox: Equilibrium Potential and the Nernst Equation.Types of Passive Transport •Simple diffusion - No membrane proteins are needed.Transport is through the bilipid layer - Facilitated diffusion - through a carrier, which is a transmembrane protein with binding sitesfor specific molecules or ions. Changes shape (conformation) as