BIO 203 Week 2 Notes: Electrochemical Gradients
BIO 203 Week 2 Notes: Electrochemical Gradients BIO 203LEC
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This 3 page Class Notes was uploaded by Andrea Tufekcic on Friday September 9, 2016. The Class Notes belongs to BIO 203LEC at University at Buffalo taught by Loretz, C A in Fall 2016. Since its upload, it has received 48 views. For similar materials see General Physiology Lec in Biology at University at Buffalo.
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Date Created: 09/09/16
Electrochemical Gradients -Main force: ionic asymmetries of cations and anions across biological membranes Macroscopic neutrality: at a large scale, the number of positives charges equals the number of negative charges (gradients caused by microimbalances) -Selective permeability (conductances) -diffusive flux of a charges solute driven by concentration gradients AND electric gradients -if gradients are oriented same way= easy to predict direction -if gradients are oriented the opposite way= harder to predict, need strengths Side one Side two 150mM NaCl 15mM NaCl 150 mM Na + 15mM NaCl 150 mM Cl - 15mM Cl - No voltage difference in the beaker, membrane permeable to Na and Cl membrane potential = ΔE mem= ΔV mem= ΔEm= ΔV =mE = m m Na and Cl shift to side 2 if membrane is permeable only to sodium, side 2 becomes electrically positive immediately after some time, ΔE levels out, Na approaches zero equilibriumvoltage=T ln?(Concou) Nernst Equation: zF Conc ¿ R= gas constant T= temperature z= valence of ion F= Faraday (96,485C/mol) *Assume that the electro and chemical gradients are equal in magnitude, opposite in direction + + Gradient Directions K EK (-90mV) Concentration Outward grad. Electrical gradient Inward Na + ENa60mV) CG Inward EG Outward + K Resting potential CG Outward (-70mV) EG Inward Na + Resting potential CG Inward (-70mV) EG Inward Conductance Charges Resting Potential Depolarized Hyperpolarized K channel open K channel open K channel open Voltage gated Na channel closed VG NA channel open VG Na channel closed Chemically gated K channel closed CG K channel closed CG K channel open Makes mV less negative Makes mV more negative Cable properties “cable theory” -passive electronic spread of an electrical signal along a cable -‘cable’= conductive cylinder (core) -surrounded by insulated layers -immersed in highly conductive solution -signal loss due to finite imperfect insulation limits useful length sol’n: increase signal strength, decrease signal loss IMAGINE: resting potential is =70mV, then something depolarizes it as Na ions enter, then shift and move down passively signal diffused out evenly back to resting potential NOT AN ACTION POTENTIAL Initial active site dist: a few mm (symmetrical diffusion) (LEARNING!)