transport across membranes

Question 1

explain how sodium potassium pump works

Answer 1

made up of 3 proteins molecules that span the cell membrane. there are 3 intracellular sites with high affinity to sodium and 2 extracellular sites with high affinity for potassium. when all these sites are occupied, the ATPase is activated and it breaks down an ATP molecule . energy is utlised to bring about a conformtaional change- the sodium sites project into the extracellular space and vice versa. therefore the ions are released: 3 Na outside of cell and 2 K enter.

Question 2

4 uses of the sodium potassium pump

Answer 2

found in large numbers in the body therefore regulate the metabolic rate- via thyroid hormones

steep sodium gradient used for secondary active transport

sodium potassium gradient across membrane is partially responsible for electrochemcial potential across nerve and muscle membranes

extrusion of Na is used to reduce osmotic flow into cell

Question 3

which type of diffusion can rech a transport maximum

Answer 3

facilitated diffusion

Question 4

what channels maintain the resting membrane potential of cells

Answer 4

sodium potassium pump and sodium leakage channel, potassium leakage channel

Question 5

membrane potential if the membran ewas only permeable to K

Answer 5

it would be -90 mV.
the conc inside is more than outside so the logXo/Xi would be negative

Question 6

membrane potential is membrane was only permeable to Na

Answer 6

would be +60mV.
conc outside higher than insdie si logX0/Xi would be positive

Question 7

was is the resting membrane potential of cells

Answer 7

-65 to -85mV
very near to potassium equilibrium potential, but not totally impermeabel to other ions especially Na