Membrane transporters

Question 1

Primary active transporters derive their energy from:

Answer 1

directly from the splitting of ATP

Question 2

Other than the _____, there are no other ubiquitous primary active transporters in the plasma
membrane of cells

Answer 2

Na/K pump

Question 3

Inside mitochondria is a very special proton pump that, when running backwards, lets

Answer 3

(the F1-ATPase)

protons leak across a membrane and synthesizes, rather than hydrolyzes ATP

Question 4

Secondary active transport Energy to do the work of pumping comes from

Answer 4

not from metabolism (ATP), but from a secondary source

• Usually this energy source is the ‘downhill leak’ of Na+ into the cell.

Question 5

Secondary active transport is

Answer 5

Mechanism by which most substances are pumped.

Question 6

There are two basic types of secondary active transporters:

Answer 6

Cotransport:

Antiport or Exchange:

Question 7

Cotransport:

Answer 7

those that move different solute species in the same direction

Question 8

Antiport or Exchange:

Answer 8

those that move solute in opposite directions

Question 9

Secondary active transport For example,cells can accumulate amino acids
This active uptake is dependent on ______

Answer 9

against their energy gradients

external Na+; if external Na+ is removed, amino acid
uptake is abolished

Conversely, removing the amino acid reduces the entry of Na+

Question 10

Secondary active transport The carrier ingeniously captures the energy released by

Answer 10

the inward leak of Na+ and instead

of letting it escape as heat, uses it to pump the amino acid into the cell.

Question 11

Secondary active transporters do not necessarily.

Answer 11

always run in the same direction

Question 12

All secondary transport mechanisms depend ultimately on the ______

Answer 12

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

Question 13

Some secondary active transporters are

Answer 13

electrogenic in that one cycle produces a net charge transfer across the membrane.
o

Question 14

Other secondary active transporters are

Answer 14

non-electrogenic.

Question 15

The main feature of electrogenic secondary active transporters is that their activity is

Answer 15

governed by the membrane potential.

Question 16

Secondary active transporters The will always tap the ____, because of this, they can _____.

Answer 16

bigger leak to drive the smaller pump.

reverse direction sometimes

Question 17

example of secondary active transporters moving in reverse

Answer 17

the sodium-calcium exchanger, which reverses direction in heart muscle cells every time the heart beats.

Question 18

Electrically silent transporters could not care less about

Answer 18

membrane potential

Question 19

if the Na+/K+ pump is blocked, cells fill up with Na+, and thus the ______ is reduced. Because this is the energy source for ______

Answer 19

Na+ electrochemical gradient

secondary active transport, all of these transport mechanisms suffer.

Question 20

For example, Na+/ amino acid transporters are electrogenic, because

Answer 20

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

Question 21

An example of non-electrogenic. is the

Answer 21

Na/K/2Cl cotransporter, which a ch cycle moves one sodium ion,one
potassium ion, and two chloride ions into the cell.

Question 22

Cotransport:

Answer 22

secondary transporters that move different solute species in the same direction

Question 23

Exchange:

Answer 23

secondary transporters that move solute in opposite directions

Question 24

A non-electrogenic secondary active transporter is one in which

Answer 24

no net charge is moved across the membrane.

Question 25

Driving Force =

Answer 25

Vm-E

Question 26

as Vm becomes more positive, the net driving force will

Answer 26

continue to decrease.

Question 27

reversal potential (Vrev);

Answer 27

it’s the value of Vm at which there will be no net movement via this exchanger.

Question 28

Vrev = Vm at which

Answer 28

there is no net movement

Question 29

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

Answer 29

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

Question 30

infusing K+ causes _____, and infusing acid causes _____

Answer 30

acidemia (the K+ is taken up by cells ‘in exchange’ for H+)

hyperkalemia

Question 31

hyperkalemia will cause _____. Hyperkalemia also will ____ cells (by shifting EK in a positive direction), and the change in membrane potential can affect ____

Answer 31

extra K+ uptake via the Na/K pump.

depolarize

the rate of activity of electrogenic transporters.

Question 32

facilitated diffusion.

Answer 32

Some transporters act like ion channels, shuttling a single solute species in either direction.

Question 33

How, then, do cells concentrate glucose? ]

Answer 33

The answer is that as soon as a glucose molecule gets into the cell, it is phosphorylated to Glucose-6-Phosphate.

Question 34

How to treat Hyperkalemia

Answer 34

C BIG K
C: calcium
B: Bicarbonate
I: insulin
G: glucose
K: kayexalate

Question 35

Hyperkalemia is very dangerous because it can lead to

Answer 35

heart arrhythmias.

Question 36

Increased extracellular potassium levels result in ______ of the membrane potentials of cells. Which results in _____

Answer 36

depolarization

This depolarization opens some voltage-gated sodium channels, but not enough to generate an action potential.

the open sodium channels inactivate and become refractory, increasing the threshold needed to generate an action potential.

This leads to the impairment of neuromuscular, cardiac, and gastrointestinal organ systems.

Question 37

Biggest concern in hyperkalemia

Answer 37

the impairment of cardiac conduction which can result in ventricular fibrillation.

Question 38

Hyperkalemia treatment with calcium

Answer 38

Ca+2 ions bind to the outside surface of cell membranes.
they trick the Na+ channels into thinking the membrane has been hyperpolarized. This increases threshold potential and restoring normal gradient between threshold for an action potential,

quieting down the aberrant, spontaneous depolarization of individual cardiac cells.

VERY LOCALIZED EFFECT!

Question 39

Hyperkalemia treatment with bicarbonate

Answer 39

The presence of excess bicarbonate ions will stimulate an exchange of cellular H+ for Na+, thus
leading to stimulation of the sodium-potassium ATPase which will stimulate uptake of K+ into the cell.

Question 40

hyperkalemia treatment with insulin and glucose

Answer 40

stimulates the Na+/K+ pump, drawing K+ into the cell from the blood

Question 41

Hyperkalemia treatment with Kayexalate

Answer 41

Ionic species in which Na+ is bound to a large, negatively charged kayexalate ion

Kayesalate prefers to bind to K+, so when introduced into K+ saturated blood, Kayexalate will exchange Na+ for K+ and sequester free K+ ions.

This is usually a longer-term treatment, so must be combined with the other short term ones to actually work (patient could die before Kayexalate would have an effect).