Membrane transporters

Question 1

Facilitated diffusion

Answer 1

transporters that shuttle ions in either direction and does not use energy

Question 2

How does glucose get into the cell?

Answer 2

It goes through the glucose transporter (res no energy) and then is phosphorylated to Glucose-6-Phosphate, which doesn’t fit in the transporter

Question 3

How does insulin regulate glucose transport?

Answer 3

Insulin triggers the cascade that causes the vesicle membranes to fuse wit the surface membrane exposing the glucose transporter to the ECF

Question 4

What transport proteins cause a substance to be accumulated or expelled against its electrochemical gradient?

Answer 4

pumps

Question 5

How do primary active transporters work?

Answer 5

derive their energy directly from ATP (like Na/K pump)

Question 6

How do secondary active transporters work?

Answer 6

Use a secondary energy source (not ATP). It’s usually the downhill leak of Na+ into the cell

Question 7

What do all secondary transport mechanisms depend upon?

Answer 7

An active pump (ex. Na/K pump)

Question 8

How does the Na/Ca exchanger work?

Answer 8

• pumps Ca2+ (1) out of the cell (keeps high ECF concentration)
• inward leak of Na+ (3) provides the energy source
• Ca2+ is pumped out with PMCA (plasma membrane Ca2+ ATPase

Question 9

How does the Na/Ca pump work in the heart?

Answer 9

• during diastole (filling), Ca2+ is pumped out and Na+ leaks in
• during systole (contraction), Ca2+ leaks in and pumps Na+ out to strengthen the force of the contraction
• Controlled by Vm

Question 10

How does digitalis work?

Answer 10

• blocks the Na/K pump
• this increases Na+ concentrations
• this reduces the energy available for all sodium driven secondary active transporters, including Na/Ca exchanger
• Ca2+ concentrations rise, increasing cardiac contractility

Question 11

How does the Na+/H+ exchanger work?

Answer 11

• secondary active transport, inward leak of Na+ drives the outward pumping of H+

Question 12

How are chloride ions pumped into some cells?

Answer 12

secondary active transport process (Na/K/2Cl cotransporter)

Question 13

What is the concept (albeit inaccurate) of a H+/K+ exchanger?

Answer 13

• if you have excess K+, you can give bicarbonate (HCO3-) to decrease the total H+ concentration in the blood
• the exchanger switches K for H making the proton concentration in the cell go down and the K+ concentration in the cell go up