Membrane Transporters Flashcards
What is primary active transport?
Pump that derives its energy directly from the splitting of ATP
What is secondary active transport?
Pumps where the energy doing the pumping does not come from ATP but a secondary source
- i.e. downhill leak of Na+ into cell
Most common type of active transport
What is cotransport?
Active transporter that moves solute species in the same direction
What is exchange (antiport) transport?
Active transporter that moves solute species in the opposite direction
What is the general model of a membrane transporter?
A tube with a gate on each end and dynamic (changeable) binding affinity
What is facilitated diffusion?
When a transporter acts like an ion channel and shuttles molecules across the plasma membrane that should not be able to cross due to their size or charge
ex: glucose transporter
Explain how the glucose transporter works:
glucose transporter sequestered inside cell -> Insulin triggers signal -> vesicle fuses with membrane and exposes glucose transporter -> Transporter carries glucose across until insulin levels subside
How do cells concentrate glucose inside? (when transporter cannot carry glucose against its concentration gradient)
As soon as glucose inside -> phosphorylated to glucose-6-phosphate
=> this does not fit on transporter -> trapped inside
How does water ALWAYS move?
Down its concentration (osmotic) gradient
- there are no water pumps anywhere in nature!
How is it that secondary active transporters do not always run in the same direction? What are the implications of this?
They use the larger leak to power the smaller pump
They are able to reverse direction
Ex) Na+/Ca2+ ion exchanger in heart reverses with each beat
On what do all secondary transport mechanisms ultimately depend?
The Na/K pump => ATP
In what direction will Ca2+ always flow given the opportunity?
Into the cell
=> this necesitates the Na/Ca pump to remove excess Ca2+
Why is it conceptually useful to think about a H+/K+ exchanger?
Because of clinical outcomes:
- Infusing K = acidemia (K exchanged for H)
- Infusing acid = hyperkalemia
=REALITY probably involves multiple pumps/transporters
How can cells be encouraged to take up potassium from ECF?
Bicarbonate: alkinilizes blood
Glucose/ insulin: provides ATP to energize Na/K pump
