Crossing the membrane
1.[2p] A flux measurement gives a straight line through the origin when plotted against external concentration, with no maximum. What does that indicate?
A flux measurement gives a straight line through the origin when plotted against external concentration, with no maximum. What does that indicate?
The answer is: Simple diffusion through the lipid, with no protein involved
The answer is: Simple diffusion through the lipid, with no protein involved
The answer is: Simple diffusion through the lipid, with no protein involved
2.[3p] How does a potassium channel pass potassium over the smaller sodium ion by more than a thousand to one?
How does a potassium channel pass potassium over the smaller sodium ion by more than a thousand to one?
The answer is: Its selectivity filter presents carbonyl oxygens spaced to replace potassium's hydration shell exactly, which does not compensate a sodium ion for the water it loses
The answer is: Its selectivity filter presents carbonyl oxygens spaced to replace potassium's hydration shell exactly, which does not compensate a sodium ion for the water it loses
The answer is: Its selectivity filter presents carbonyl oxygens spaced to replace potassium's hydration shell exactly, which does not compensate a sodium ion for the water it loses
3.[3p] Using mV at 310 K, what is the Nernst potential for potassium in millivolts, with 140 mM inside and 5 mM outside? Give a negative number.
Using mV at 310 K, what is the Nernst potential for potassium in millivolts, with 140 mM inside and 5 mM outside? Give a negative number.
4.[1p] The sodium potassium ATPase moves three sodium ions out and two potassium ions in per ATP, so it contributes directly to the membrane voltage.
The sodium potassium ATPase moves three sodium ions out and two potassium ions in per ATP, so it contributes directly to the membrane voltage.
The answer is: True
5.[3p] Match each transport protein to its behaviour.
Match each transport protein to its behaviour.
A potassium channel
GLUT1
The sodium potassium ATPase
SGLT1
about 1000 molecules per second, downhill only
about 100 ions per second, uphill, one ATP per cycle
uphill for glucose, powered by two sodium ions falling downhill
passes about ions per second, downhill only
Show the answer
A potassium channel: passes about ions per second, downhill only GLUT1: about 1000 molecules per second, downhill only The sodium potassium ATPase: about 100 ions per second, uphill, one ATP per cycle SGLT1: uphill for glucose, powered by two sodium ions falling downhill
6.[3p] Roughly what fraction of a cell's potassium has to cross the membrane to establish a resting potential of 70 mV?
Roughly what fraction of a cell's potassium has to cross the membrane to establish a resting potential of 70 mV?
The answer is: About three in a hundred thousand
The answer is: About three in a hundred thousand
The answer is: About three in a hundred thousand
7.[2p] Which of these are ways cells avoid bursting from the osmotic pressure of their own contents?
Which of these are ways cells avoid bursting from the osmotic pressure of their own contents?
Select all that apply
The answer is: Pumping sodium out, so that it acts as an impermeant external solute, Building a rigid wall and allowing turgor pressure to rise, Expelling water with a contractile vacuole
8.[3p] Why does digoxin, which blocks the sodium potassium ATPase, strengthen heart muscle contraction?
Why does digoxin, which blocks the sodium potassium ATPase, strengthen heart muscle contraction?
The answer is: Internal sodium rises, so the sodium calcium exchanger expels less calcium, and internal calcium rises
The answer is: Internal sodium rises, so the sodium calcium exchanger expels less calcium, and internal calcium rises
The answer is: Internal sodium rises, so the sodium calcium exchanger expels less calcium, and internal calcium rises
9.[2p] Why does oral rehydration therapy need both salt and sugar rather than either alone?
Why does oral rehydration therapy need both salt and sugar rather than either alone?
The answer is: SGLT1 carries sodium and glucose together, so neither is absorbed efficiently without the other, and water follows both
The answer is: SGLT1 carries sodium and glucose together, so neither is absorbed efficiently without the other, and water follows both
The answer is: SGLT1 carries sodium and glucose together, so neither is absorbed efficiently without the other, and water follows both