PSC2002/L02 Membrane Transport I Flashcards
Give 2 types of macrotransfer movement.
Endocytosis
Exocytosis
What is microtransfer?
Smaller scale movement
Cell membrane transport of small molecules and ions
What is Clathrin?
‘Bendy’ protein that mediates endo/exocytosis
Composed of 3 heavy chains & 3 light chains
Coats inner surface of membrane and assembles into basket-like structure
Once vesicle is formed, clathrin coat is shed and vesicle merges with other cellular components
How permeable is a phospholipid membrane (with no protein) to the following molecules:
a) Hydrophobic
b) large polar
c) small uncharged polar
d) Ions?
a) Very highly
b) low
c) high
d) impermeable
Resting membrane potential is mostly due to which 2 ions?
Na+ and K+
What is the Nernst equation?
(Em) = (RT/zF) Ln ([X]o/[X]i)
Em = membrane potential
R = Gas constant (8.314)
T = temp (K)
z = no. charges on ion
F = Faraday’s no (96485.3 C.mol^-1)
[X]o/i = conc of ion out/inside
What is predicted by the Nernst equation?
Equilibrium membrane potential based on concentration gradient of ion across membrane (Nernst potential)
How is the Goldman-Hodgkin-Katz equation different to the Nernst equation?
GHK equation takes into account all ions and their respective permeabilities
What is the permeability ratio of non-excitable cells?
2:1
K+:Na+
What is the permeability ratio of nerve/muscle cells?
25:1
K+:Na+
What is the most powerful electrophysiological method for basic research?
Voltage clamp
What can be determined by a voltage clamp experiment?
Detailed measurement and analysis of electrical activity across a tissue, cell or artificial membrane mediated by specialised ion channels and electrogenic carriers
When combined with molecular biology, what can be found from a voltage clamp?
Fundamental information on structure, function and regulation of transport proteins
Describe the process of using a voltage clamp. (3)
Investigator sets holding voltage
Voltage clamp uses negative feedback to maintain cell at command potential
Apparatus compensates for changes in current to maintain constant membrane potential
When and who was the voltage clamp first developed by?
Cole and Marmont in 1930-1940s
First used in giant squid axon
What is a patch clamp?
Recording pipette physically isolates a patch of membrane on cell surface
Can electrically clamp potential across patch to measure current flow through single ion channel
Describe the basis of the patch clamp.
Formation of high resistance seal between membrane and micropipette
Giga-seal means current flowing through ion channels in patch can be recorded with low noise
What are co-transporters/symporters?
Movement of a solute coupled to movement of another down its concentration gradient
What are counter-transporters/antiporters?
Coupled movement of two or more solutes in opposite directions
What is the equation for flux (flow)?
J = P./\C
P = permeability
/\C = conc difference
What is the equation for permeability?
P = Dk/x
D = diffusion constant
k = partition constant
x = distance
What are the 3 kinds of transporters that facilitate diffusion?
Channels (non-gated)
Gated channels
Uniporters
Which channels allow direct access to:
a) cells
b) bacteria, mitochondria, NPC?
a) Aquaporins
b) Porins
What are the 3 functional components of gated channels?
Gate
Sensor
Selectivity filter
What can gated channels be modulated by? (3)
Voltage
Mechanical stimuli
Ligand binding
Describe the 6 steps of facilitated diffusion.
Carrier open
Solute binds and enters
Outer gate opens
Inner gate opens
Solute released
Inner gate closes
Which carrier-mediated transporters are found:
a) in RBC
b) in intestines
c) in skeletal/cardiac muscle?
a) GLUT1
b) GLUT2
c) GLUT 4
