Membrane Transporters

Question 1

Primary active transporters derive their energy directly from the

Answer 1

splitting of ATP

Question 2

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:

Answer 2

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

Question 3

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

Answer 3

• protons

- calcium ions

Question 4

Inside cells (as opposed to the surface membrane) there are other primary active transporters. One pumps protons into _______. Another pumps calcium ions into _______

Answer 4

• intracellular membrane-bound organelles (endosomes, vesicles, lysosomes)
• membrane-bound compartments

Question 5

Inside mitochondria is a very special _______ pump (the _______) that, when running backwards, lets _______ and _______

Answer 5

• proton
• the F1-ATPase
• protons leak across a membrane
• synthesizes, rather than hydrolyzes ATP

Question 6

Secondary active transport

Answer 6

• 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

Question 7

This active uptake is dependent on external Na+; if external Na+ is removed, amino acid uptake is _______

Answer 7

abolished

Question 8

removing the _______ reduces the entry of Na+

Answer 8

amino acid

Question 9

The carrier ingeniously

Answer 9

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.

Question 10

There are two basic types of secondary active transporters:

Answer 10

• Cotransport: those that move different solute species in the same direction
• Antiport or Exchange: those that move solute in opposite directions

Question 11

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 _______

Answer 11

• bigger
• smaller
• reverse direction
• sodium-calcium exchanger
• reverses direction in heart muscle cells every time the heart beats.

Question 12

All secondary transport mechanisms depend ultimately on the _______

Answer 12

-Na+/K+ pump (and therefore on ATP)

Question 13

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, _______

Answer 13

• Na+
• reduced
• all of these transport mechanisms suffer

Question 14

electrogenic

Answer 14

one cycle produces a net charge transfer across the membrane

Question 15

_______ transporters are electrogenic, because _______

Answer 15

• Na+/amino acid

- one cycle transfers a net positive charge (Na+) into the cell

Question 16

non-electrogenicn example is the _______, which _______

Answer 16

• Na/K/2Cl cotransporter

- each cycle moves one sodium ion, one potassium ion, and two chloride ions into the cell

Question 17

The main feature of electrogenic secondary active transporters is that their activity is governed by the _______. Electrically silent transporters could care less about it

Answer 17

membrane potential

Question 18

Cotransport:

Answer 18

secondary transporters that move different solute species in the same direction

Question 19

Exchange:

Answer 19

secondary transporters that move solute in opposite directions

Question 20

A non-electrogenic secondary active transporter is one in which

Answer 20

no net charge is moved across the membrane.

Question 21

Driving Force =

Answer 21

Vm-E

Question 22

Vrev =

Answer 22

Vm at which there is no net movement

Question 23

At values of Vm more positive than Vrev, the exchanger will run

Answer 23

in the other direction: moving H+ into the cell and pumping Na+ out of the cell

Question 24

infusing K+ causes _______, and infusing acid causes _______

Answer 24

• acidemia (the K+ is taken up by cells ‘in exchange’ for H+)
• hyperkalemia (elevated (hyper-) potassium (-kal- for Latin kalium) in the blood (-emia))

Question 25

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 _______

Answer 25

• K+
• the Na/K pump
• depolarize
• electrogenic transporters