Membrane Transporters Flashcards
Primary active transporters derive their energy directly from the
splitting of ATP
Other than the Na/K pump, there are no other ubiquitous primary active transporters in the plasma membrane of cells. Some specialized cells have them:
the cells in the stomach that secrete acid, and certain cells in the kidney geared for excreting protons from the body possess proton pumps that rely directly on ATP for their energy source
Inside cells (as opposed to the surface membrane) there are other primary active transporters. One pumps _______ into intracellular membrane-bound organelles (endosomes, vesicles, lysosomes). Another pumps _______ into membrane-bound compartments
- protons
- calcium ions
Inside cells (as opposed to the surface membrane) there are other primary active transporters. One pumps protons into _______. Another pumps calcium ions into _______
- intracellular membrane-bound organelles (endosomes, vesicles, lysosomes)
- membrane-bound compartments
Inside mitochondria is a very special _______ pump (the _______) that, when running backwards, lets _______ and _______
- proton
- the F1-ATPase
- protons leak across a membrane
- synthesizes, rather than hydrolyzes ATP
Secondary active transport
- Mechanism by which most substances are pumped.
- Energy to do the work of pumping comes not from metabolism (ATP), but from a secondary source
- Usually this energy source is the ‘downhill leak’ of Na+ into the cell
This active uptake is dependent on external Na+; if external Na+ is removed, amino acid uptake is _______
abolished
removing the _______ reduces the entry of Na+
amino acid
The carrier ingeniously
captures the energy released by the inward leak of Na+ and instead of letting it escape as heat, uses it to pump the amino acid into the cell.
There are two basic types of secondary active transporters:
- Cotransport: those that move different solute species in the same direction
- Antiport or Exchange: those that move solute in opposite directions
Secondary active transporters will always tap the _______ leak to drive the _______ pump. Consequently, they can _______ sometimes. One of the most important examples of this is the _______, which _______
- bigger
- smaller
- reverse direction
- sodium-calcium exchanger
- reverses direction in heart muscle cells every time the heart beats.
All secondary transport mechanisms depend ultimately on the _______
-Na+/K+ pump (and therefore on ATP)
If the Na+/K+ pump is blocked, cells fill up with _______, and thus the Na+ electrochemical gradient is _______. Because this is the energy source for secondary active transport, _______
- Na+
- reduced
- all of these transport mechanisms suffer
electrogenic
one cycle produces a net charge transfer across the membrane
_______ transporters are electrogenic, because _______
- Na+/amino acid
- one cycle transfers a net positive charge (Na+) into the cell
non-electrogenicn example is the _______, which _______
- Na/K/2Cl cotransporter
- each cycle moves one sodium ion, one potassium ion, and two chloride ions into the cell
The main feature of electrogenic secondary active transporters is that their activity is governed by the _______. Electrically silent transporters could care less about it
membrane potential
Cotransport:
secondary transporters that move different solute species in the same direction
Exchange:
secondary transporters that move solute in opposite directions
A non-electrogenic secondary active transporter is one in which
no net charge is moved across the membrane.
Driving Force =
Vm-E
Vrev =
Vm at which there is no net movement
At values of Vm more positive than Vrev, the exchanger will run
in the other direction: moving H+ into the cell and pumping Na+ out of the cell
infusing K+ causes _______, and infusing acid causes _______
- acidemia (the K+ is taken up by cells ‘in exchange’ for H+)
- hyperkalemia (elevated (hyper-) potassium (-kal- for Latin kalium) in the blood (-emia))
hyperkalemia will cause extra _______uptake via the _______. Hyperkalemia also will _______ cells (by shifting EK in a positive direction), and the change in membrane potential can affect the rate of activity of _______
- K+
- the Na/K pump
- depolarize
- electrogenic transporters
