membrane transport Flashcards
what hydrophobic molecules can get through the bilayer
O2, N2, CO2, benzene, short chain FA
small uncharged polar molecules that get thought
h2o, urea, glycerol
what can’t get through
large uncharged polar molecules, ions, charged polar molecules
describe facilitated diffusion and give an example
protein along conc gradient no energy can involve conformational change in selective carrier protein e.g. GLUT - glucose
examples of primary and secondary active transport
primary; Na/K ATPase
secondary: Na/glucose transporter
what does the rate of diffusion depend on
partition coefficient:
K(ow) - equilibrium constant for partitioning of a molecule between oil (octanol) and water
what does a high Kow value mean
more lipid soluble
uniport/symport/antiport
uni:
symp:
anti:
GLUT1 location and main function
- high in erythrocytes and blood brain barrier, low in skeletal muscle
- glucose uptake
GLUT2
- liver, pancreas B cells
- highi Km and large Jmaz
- transport glucose into hepatocytes and B cells to when [gluc] high to regulate blood
GLUT3
low Km
highest expression in neurones
GLUT4
- muscle, adipocytes
- regulated by insulin: bring GLUT4 to plasma membrane
GLUC5
-fructose transporter
difference between primary and secondary active trnsport
primary: hydrolysis of ATP
secondary: electrochemical gradient
examples of primary active trans
- NA/K-ATPase in plasma membrane
- H-ATPase in lysosomal membarane
- Ca-ATPase in plasma membrane and sarcoplasmic reticulum of muscle
what type of process is secondary active trans
electrogenic: produce change electrical potential of cell
why is NA/K-ATPase a drug target in heartfeailutre
- oubain blocks pump - prevent K binding
- increase intracellular [Na]
- inhibits Na/Ca antiporter
- increase in intracellular[Ca] = trigger cardiac muscle contrction
what is purple foxglove a source of
digitoxin and digoxin – cardiotonic drugs, increase contraction
what is secondary active trans important in
- intestinal epithelial cells - absorb glucose
2. epithelial cells in PCT - reabsorb glucose
e.g. of secondary A transprter
Na/Gluc transporter
SGLUT1
what does cholera do
- Vibrio cholerae = causes electrolyte and fluid secretion
- toxin = Cl excreted by over activating Gsa = activate adenylyl cyclase and increase cAMP
Role of the Na+/Glucose Cotransporter in Electrolyte Replacement Therapy in Cholera
a high concentration of glucose (~110 mM) which drives Na+ (and consequently Cl- and H2O) back into the intestine through the Na+/glucose cotransporter
how is the transport of glucose aided
Binding of D-glucose to an extracellular domain causes the conformational change, polar amino acids within the bilayer core Hydrogen bond to the hydroxyl groups of glucose thereby facilitating its movement
