Transporter proteins Flashcards
What are the extracellular and intracellular concentrations of sodium?
Extracellular - 140mM
Intracellular - 14mM
What are the extracellular and intracellular concentrations of potassium?
Extracellular - 5mM
Intracellular - 160mM
What are the extracellular and intracellular concentrations of calcium?
Extracellular - 1mM
Intracellular - 100nM
What are the relative extracellular and intracellular concentrations of chloride ions?
Extracellular concentration is higher than intracellular one
Where is Na+ K+ ATPase located?
Plasma membrane of all cells
What does Na+ K+ ATPase do?
Actively transports 3 sodium out of the cell
2 potassium ions into the cell
using energy from ATP hydrolysis
What type of transport does Na+ K+ ATPase do?
Active transport
Co-transport, antiport
What is the structure of Na+ K+ ATPase?
Two subunits
- alpha subunit
- beta subunit
What does the alpha subunit of Na+ K+ ATPase do?
Binds sodium, potassium, ATP
What is the structure of the beta subunit of Na+ K+ ATPase?
It has oligosaccharide chains on its surface
making it a glycoprotein
What does the beta subunit of Na+ K+ ATPase do?
Directs the protein to the cell surface
How exactly does Na+ K+ ATPase use the energy released from ATP hydrolysis to actively transport sodium and potassium ions?
ATP phosphorylares the alpha subunit
producing an intermediate transporter
How responsible is the Na+ K+ ATPase for producing the resting membrane potential?
Has a very minor role
What is largely responsible for producing the resting membrane potential?
Plasma membrane is more permeable to potassium ions
move out of the cell through open potassium ion channels
How does Na+ K+ ATPase contribute to the resting membrane potential?
Sets up the sodium and potassium concentration gradients required
What does the NCX do in normal conditions?
Transports 3 sodium ions into the cell by facilitated diffusion
Actively transports 1 calcium ion out of the cell
What type of transport does NCX do?
Co-transport, antiport
How does the NCX affect the charge of the plasma membrane?
One positive charge entering the cell
What does NCX do when the membrane is depolarised?
Works in reverse
transports 3 sodium ions out
1 calcium ion in, both by facilitated diffusion
What does NCX do during ischaemia? Why?
Works in reverse
because ATP is depleted
Na+ K+ ATPase cannot function
sodium ions accumulate inside the cell
membrane becomes depolarised
What does NCX working in reverse lead to?
High intracellular calcium concentration
toxic to cell
What are the transporters involved in controlling cell pH?
Na+ H+ exchanger (NHE)
Na+ dependent Cl- HCO3- exchanger (NBC)
Cl- HCO3- exchanger (AE)
What does NHE do?
Transports one sodium ion into the cell by facilitated diffusion
Transports one hydrogen ion out of the cell
What type of transport does NHE do?
Co-transport, antiport
How does NHE affect the pH of a cell?
Raises the pH of the cell
What does NBC do?
Transports one sodium ion and one bicarbonate ion into the cell
Transports one hydrogen ion and one chloride ion out of the cell
How does NHE affect the charge of the plasma membrane?
It doesn’t
equal charges going across plasma membrane
What type of transport does NBC do?
Co-transport, antiport
How does NBC affect the pH of a cell?
Raises the pH of the cell
How does NBC affect the charge of the plasma membrane?
It doesn’t
equal charges moving across plasma membrane
What does AE do?
Transports chloride ion into the cell
bicarbonate ion out of the cell
What type of transport does AE do?
Co-transport, antiport
How does AE affect the pH of the cell?
Lowers the pH of the cell
How does AE affect the charge of the plasma membrane?
It doesn’t
equal charges moving across plasma membrane
What type of cell is rich in AE on its plasma membrane?
Red blood cells
How does AE on the plasma membrane of red blood cells affect them?
Makes red blood cells more acidic
lowers affinity of haemaglobin for oxygen
released to tissues
How does AE on the plasma membrane of red blood cells affect the blood?
Bicarbonate ion released into blood as pH buffer
How is cell volume controlled?
By transporting osmotically active ions into/out of cells
water follows by osmosis
What are some examples of osmotically active ions?
Sodium
Potassium
Chloride
What are some examples of transporters decrease cell volume? How?
Potassium ion channels - potassium ions leave cell through them
What are some examples of transporters that increase cell volume? How?
Sodium ion channels - sodium ions enter cell through them
NHE - sodium ion enters cell
AE - chloride ion enters cell
