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Movement of Molecules Across Membranes

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Movement of Molecules Across Membranes Movement of Molecules Across Membranes Sue Keirstead, Ph.D. Assistant Professor Dept. Integrative Biology and Physiology Stem Cell Institute 612 626 2290 [email protected] Movement of Molecules Across Membranes - Learning Objectives 1. List the chemical characteristics of molecules that are most likely to move by simple diffusion across the lipid bilayer of the plasma membrane and explain why. Explain the factors that Fick’s Law tells us determine the rate of diffusion through the lipid bilayer. 2. Explain why ions do not move through ion channels by only simple diffusion, whereas water does move through water channels by simple diffusion. Specifically, what, in addition to the concentration gradient, affects the movement of ions through ion channels? 3. Compare and contrast the ways in which channels and carrier proteins facilitate movement of ions across the plasma membrane. Consider specificity, energy requirements, mechanism of movement of solute, and saturation. 4. Differentiate the following processes based on 1) the necessity for and 2) source of energy driving the process and 3) the molecular pathway for: simple diffusion through the lipid bilayer, facilitated diffusion by carrier proteins, secondary active transport, and primary active transport. 5. Define saturation and explain how and why the transport of a molecule by a saturable mechanism such as facilitated diffusion by carrier proteins will differ from simple diffusion through the lipid bilayer. Draw a graph showing the rate of solute movement versus extracellular concentration for the two processes (see Figures 5.6 & 5.10). 6. Understand how a cell could be modified to increase or decrease the maximal rate of transport across the plasma membrane by carrier-mediated mechanisms (e.g. upregulation). Draw a second line on the graph in LO 5 to show the rate of transport after upregulation of the carrier proteins. 7. Describe how the distribution of proteins on the luminal (apical) and basolateral membranes of an intestinal epithelial cell permits the transcellular transport of glucose, sodium, and water from the lumen of the intestine to the interstitial fluid (see Figure 5.25). Consider the movement of glucose across the apical and basolateral membranes after a meal versus after a long night’s sleep (i.e. fasting). External environment O2 CO2 Integumentary system Nutrients Digestive system Cells Respiratory Internal environment system Interstitial Blood plasma fluid O2 CO2 Nitrogenous Nutrients wastes Nutrients Nitrogenous wastes Cardiovascular system Urinary system Urine Solid wastes Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Fig 1.4 Small Intestine - Digestion - Absorption Fig 21.17 Mechanisms for Digestion: Enzymes Fig 21.18 Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Mechanisms for nutrient absorption Absorptive Blood capillary Glucose and Secondary active cell Mono- of a villus galactose transport with Na+ Transport saccharides proteins Facilitated Facilitated diffusion Fructose diffusion Lacteal of Secondary active a villus + Amino acids transport with Na or facilitated Amino acids Dipeptides diffusion Facilitated Secondary active diffusion Tripeptides transport with H+ Short-chain fatty acids Simple Short-chain Simple diffusion fatty acids diffusion Triglycezride Chylomicron Long-chain fatty acids Simple diffusion Monoglycerides Micelle Microvillus of brush border on apical surface Basolateral surface Fig 21.20 Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Lumen Apical (luminal) membrane 1 EPITHELIAL CELLS 2 3 Basolateral membrane 4 Interstitial fluid Blood capillary Fig 5.25 Diffusion across the lipid bilayer Extracellular fluid Nonpolar Small, uncharged Ions: Large, uncharged molecules: polar molecules: polar molecules: + + – O2, CO2, steroids H2O, urea Na , K , Cl Glucose Plasma membrane Cytosol Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Fig 5.1 Extracellular fluid Plasma membrane Cytosol Concentration gradient (c) Carrier-mediated Simple diffusion Channel-mediated facilitated diffusion facilitated diffusion Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Relationship between the rate of diffusion and the concentration gradient of the solute Diffusion rate Diffusion of solute Concentration gradient of solute Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Fig 5.6 Movement through channels Extracellular fluid Plasma membrane Cytosol Concentration gradient (a) Simple (b) Channel-mediated (c) Carrier-mediated diffusion facilitated diffusion facilitated diffusion Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Fig 5.5 Carrier protein-mediated Transport Primary Active Transport Facilitated Diffusion ATP ADP Secondary Active Transport Compare and contrast K+ electrochemical gradient Extracellular fluid Plasma membrane Cytosol K+ K+ concentration K+ electrical K+ electrochemical gradient gradient gradient LO 2 What, in addition to concentration gradient, affects the movement of ions through ion channels? Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Fig 5.3 Gated K+ channel Extracellular fluid Plasma membrane Cytosol Low [K+] Channel protein K+ electrochemical Pore gradient K+ Gate open Gate closed High [K+] Fig 5.7 Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Extracellular fluid Plasma membrane Cytosol Solute to be transported Carrier protein A Carrier protein B Carrier protein C Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Facilitated Diffusion Solute to be transported Extracellular fluid Carrier protein Solute concentration Conformational gradient change Intracellular fluid Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Extracellular fluid Plasma membrane Cytosol High [glucose] Glucose Glucose transporter 1 2 Glucose concentration gradient 3 Glucose Low [glucose] Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. 3. Compare and contrast the ways in which channels and carrier proteins facilitate movement of ions across the plasma membrane. Consider specificity, energy requirements, mechanism of movement of solute, and saturation (see CT 1.5). Diffusion rate rate Diffusion of solute Concentration gradient of solute Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Transport maximum (Tm) Transport rate ofsolute Transport Concentration gradient of solute Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. LO 5 & 6 Fig 5.10 Primary Active Transport High [Na+] Low [K+] Extracellular fluid Na+/K+ ATPase 3 Na+ expelled 2K+ Na+ electrochemical K+ electrochemical gradient gradient P 3 Na+ ATP ADP P 2 K+ imported Intracellular fluid 1 2 3 4 Low [Na+] High [K+] Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Secondary Active Transport Extracellular fluid High [Na+] Low [solute] Solute to be Na+ Carrier protein cotransported Na+ electrochemical Solute concentration gradient gradient 1 2 3 4 Low [Na+] / High [solute] Intracellular fluid Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Na+/ glucose symporter (cotransporter) Extracellular fluid High [Na+] Low [glucose] Na+ electrochemical Glucose concentration gradient gradient + Na Glucose + Intracellular fluid Low [Na ] High [glucose] Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Na+/ amino acid symporter Extracellular fluid Cytosol High [Na+] Low [amino acid] Na+ electrochemical Amino acid concentration gradient gradient Amino Na+ acid Low [Na+] High [amino acid] Intracellular fluid e.g. glutamate Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Na+/ Ca2+ antiporter (exchanger) Extracellular fluid High [Na+] High [Ca2+] Ca2+ Na+ electrochemical Ca2+ electrochemical gradient gradient Na+ Low [Na+] Low [Ca2+] Intracellular fluid Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. Na+/ H+ antiporter Extracellular fluid Plasma membrane Cytosol HIgh [Na+] / High [H+] H+ Na+ electrochemical H+ electrochemical gradient gradient Na+ Low [Na+] / Low [H+] Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved. .
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