Membrane Transport Flashcards
Describe pore facilitated diffusion.
Glucose Transport (integral membrane protein)
12 membrane spanning helices
increases transport rate 50,000 times
transports D-glucose more readily than L.
What are the four steps in active transport of Na and K?
3 Na bind cytosolic binding site of pump
pump phosphorylated by ATP –> conformational change releasing Na
2 K bind extracellular binding site
phosphate group released and pump returns to original conformation.
why is one molecule of ATP enough.
under physiological conditions there is more ATP than ADP or Pi in cell, so actual free energy change is ~-45-50kJmol-1
total energy needed is ~42kJ per mole
What are the three steps in Na-Glc co-transport?
Na likely to bind to symport in lumen, making Glc binding more likely
symport changes when both bound.
Due to high [] Glc & low Na, don’t leave by same route as binding of both to symporter is rare –> unidirectional.
Glc leaves basal side of cell by facilitated diffusion.
Give an example of carrier facilitated diffusion.
Valinomycin, antibiotic produced by Streptomyces.
Interior with N and O’s chelates one K+
Exterior hydrophobic
diffuses across membrane, carrying K+ down [] gradient and hyperpolarising cell!
What is significant about aspirin?
MODIFICATION
In mucosa, pH of 1.2 causes ionised form to accept a proton (pKa 3).
Unionised form crosses membrane to gastric cell
higher pH (7.4) causes ionisation, trapped in gastric cell.
what is the structure of sphingosine?
long acyl chain with amino group and two oh groups at one end.
sphingomyelin formed by attaching FA tail.
what is pkc an example of?
binds cytosolic face of membrane where phosphatidylserine is [] because it needs negative charge for activity.
MEMBRANE ASSYMETRY.
what is significant about glycoproteins / glycolipids?
What are their functions?
oligosaccharides are added in golgi / ER so exlusively cytosolic.
protect cell surface from mechanical damage
adsorb water –> slimy layer aiding motility
cell-cell recognition (diverse).
What us the structure & mechanism of an aquaporin?
narrow pore –> carbonyl oxygens on one side
hydrophobic aas on other
water in single file
hydrated ions too large to fit but dehydration
energetically unfavourable.
