PSC2002/L03 Membrane Transport II Flashcards
Give 2 examples of P-type ATPases that phosphorylate themselves during pumping cycle.
Na+-K+ pumps
Ca2+ pumps in SR
Give 2 inhibitors of Na+-K+ pumps.
Ouabain (strophantus)
Cardiac glycosides from digitalis spp
Describe the structure of a Na+/K+ pump.
11 transmembrane domains
3 cation binding sites I, II, III
Actuator domain
Phosphorylation domain
Nucleotide domain
Ouabain extracellular domain
Describe why the Na+/K+ pump transports unequal numbers of ions.
2 K+ for 3 Na+
K+ ions larger
Na+ fits into domains more easily
Describe the mechanism of the Na+/K+ pump. (10)
Na+ enters channel
Conformational change moves N domain
N domain phosphorylates P domain (ATP hydrolysed)
Gate shut and open other side using energy
Na+ released
K+ enters and fills vacant pockets
Conformational change to release phosphate from P domain through actuator domain
Regenerated ATP binds N domain & energy used to open gate
K+ exits
Actuator domain resets and cycle repeats
What are the 5 phases of the Na+/K+ pump mechanism?
E1 -> E1Na -> E1-P -> E2-P -> E2K
What is the Gibs-Donnan effect?
Describes unequal distribution of permanent ions on either side of a membrane which occurs in presence of impermanent charged ions
Describe counteraction of the Gibbs-Donnan effect.
Negatively charged proteins & dissolved solutes hold onto positive ions in cell
= low water potential
Water enters cell
Na+/K+ ATPase lowers number of dissolved particles inside cell
Ouabain inhibited
Define secondary transporters. (3)
Use kinetic energy provided by electrochemical gradients
Transport one solute down a concentration gradient
Coupled to transport of another against concentration gradient
Define symporters/co-transporters.
Integral membrane proteins involved in transport of two or more molecules or ions in same direction
E.g., Na+/glucose transporter
Give 2 examples of symporters.
Amino acid transporter
Na+/phosphate transporter
Na/K/Cl transporter
Na+/HCO3 cotransporter
Cl-/K+ symporter
Define antiporters.
Integral membrane proteins involved in the transport of two or molecules or ions in opposite directions
Give an example of an antiporter.
Na+/H+ (NHE)
Na+/Ca2+ (NCX)
Describe ATP binding cassette transporters (ABC transporters).
Transport small molecules (can remove toxins)
Includes CFTR
Describe the structure of ABC transporters. (3)
Two membrane spanning domains
Two nucleotide binding domains
R - regulatory domain
What defines the probability of ABC-transporter opening? (2)
Presence of ATP in NBD and phosphorylation of R domain increases probability
Give an example of an atypical ABC-transporter.
CFTR
What is the difference between osmolarity and osmolality?
Osmolarity: total concentration of dissolved particles in a litre (osmol/L)
Osmolality: number of dissolved particles per unit mass (osmol/H2O)
Define osmotic pressure.
Pressure exerted by flow of water across membrane
Determined by solutes concentrations
Define tonicity.
Measure of the effect a solution has on cells placed in it and is driven by osmolarity
What occurs to a cell in:
a) Hypotonic
b) hypertonic
c) isotonic solution?
a) cell expands
b) cell shrinks
c) no change
What is the equation for Flux (flow)?
J = P./\C
J = flux
P = permeability
/\C = conc. difference
What is the equation for permeability?
P = Dk/x
D = diffusion coeficient
k = partition constant
x = distance
What is the equation for water flow?
Jv = Lp x /\P
Jv = water flow
Lp = hydraulic water pressure
/\P = pressure
