Facilitated Diffusion by Carrier Proteins, Secondary Active Transport, and Primary Active Transport

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

CO2

Nitrogenous Nutrients wastes Nutrients Nitrogenous wastes

Cardiovascular system Urinary system

Urine Solid wastes

Fig 21.17 Mechanisms for Digestion: Enzymes

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

EPITHELIAL CELLS

2 3

Basolateral membrane

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

Concentration gradient

Concentration gradient of solute

Extracellular fluid Plasma membrane Cytosol

Concentration gradient

(a) Simple (b) Channel-mediated (c) Carrier-mediated diffusion facilitated diffusion facilitated diffusion

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?

Extracellular fluid Plasma membrane Cytosol

Low [K+]

Channel protein

K+ electrochemical Pore gradient

K+ Gate open Gate closed

High [K+]

Solute to be transported

Carrier protein A Carrier protein B Carrier protein C

Primary Active Transport

Facilitated Diffusion

ATP ADP

Secondary Active Transport

Compare and contrast Facilitated Diffusion

Solute to be transported

Extracellular fluid

Carrier protein

Solute concentration Conformational gradient change

Intracellular fluid

High [glucose]

Glucose Glucose transporter

Glucose concentration gradient

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

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+]

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

Extracellular fluid High [Na+] Low [glucose]

Na+ electrochemical Glucose concentration gradient gradient

+ Na Glucose

+ Intracellular fluid Low [Na ] High [glucose]

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

Extracellular fluid High [Na+] High [Ca2+] Ca2+

Na+ electrochemical Ca2+ electrochemical gradient gradient

Na+

Low [Na+] Low [Ca2+] Intracellular fluid

Extracellular fluid Plasma membrane Cytosol

HIgh [Na+] / High [H+] H+

Na+ electrochemical H+ electrochemical gradient gradient

Na+ Low [Na+] / Low [H+]