Membrane Transport Flashcards
(18 cards)
What is conductance measured in ?
Picosiemens (pS)
What is gating?
Fluctuation between open and closed states
What factors control gating on ion channels ?
- Membrane voltage
- Extracellular agonist or antagonists
- Intracellular messengers
- Mechanical stretch of the plasma membrane
What are ionotropic receptors?
Nicotinic receptors.
Fast acting
Activation of receptor causes a pore to open through which ions can pass.
What are metabotropic receptors?
GPCRs
Slower response
Activation of receptor initiates an intracellular signalling mechanism
Gs: stimulatory
Gi: inhibitory
What are the 3 major groups of solute carriers?
- Uniporters
- Symporters
- Antiporters
What are uniporters ?
Transport a single molecule across a membrane
Eg. Glut2- brings glucose into the cell
Mutations can cause diabetes
What are symporters ?
Couple the movement of two or more molecules/ions across the membrane. Molecules transported in the same direction.
Eg. NKCC2- found in the kidneys, important for diluting and concentrating urine
What are antiporters?
Couple movement of two or more molecules/ions across the membrane in opposite directions.
Also called exchangers and counter transporters.
Eg. Na-H exchanger- found in all cells, important in regulating PH
What is an example of an ATP dependent ion transporter ?
Na+,K+ATPase which is found in all cells.
It consists of 3 subunits- alpha, beta and FXYD.
Alpha subunit has binding sites for: Na+, K+, ATP and Ouabain
What is ouabain ?
A medicine that inhibits Na+/K+ pump.
It is prescribed for arithmias and heart palpitations.
What is primary active transport ?
Transport is directly coupled to ATP hydrolysis (to move substances against their concentration gradient)
What is secondary active transport?
Energy for the transport comes from the electrochemical gradient. The energy from one molecule is used to move another molecule against its electrochemical gradient
What is an example of primary active transport?
Sodium-potassium pump
What is an example of secondary active transport?
Sodium-glucose symporter
What are ABC transporters ?
ATP-Binding Cassette transporters.
They use energy from ATP hydrolysis.
Eg. Cystic fibrosis transmembrane regulator (CFTR), functions as a chloride ion channel
What are water channels ?
Aquaporins
They facilitate the movement of water molecules across cell membranes.
What are the differences between facilitated diffusion and active transport ?
FD doesn’t require ATP, AT does
FD is down the conc gradient, AT is against the conc gradient
FD uses proteins, AT uses pumps
