Transporters' Functions

Question 1

Sodium and Potassium Homeostasis

Answer 1

Na/K ATP-ase (P-port)

Question 2

Chloride gradient (normal cells)

Answer 2

Chlorine extruded from cells by the electrical gradient established by high levels of internal potassium

Question 3

Chloride gradient (neurons)

Answer 3

K/Cl cotransporters push Cl out using K gradient

Question 4

pH

Answer 4

Na/H antiport; when cytoplasmic pH drops, Na is pumped in and H is pumped out

Question 5

Redundant pH

Answer 5

Na/HCO3 transporters are redundant system, Na is exchanged for HCO3

Question 6

Water removal (shrinking)

Answer 6

Cl channels open and due to the increased positive charge across the membrane, K follows; water follows salt

Question 7

Increasing water (swelling)

Answer 7

Na/K/2Cl pumps activated (direct injection of ions); Na/H exchange is begun which causes the pH to rise -> H removal causes carbonic anhydrase to create more H and HCO3 -> pH rises further and anion exchange happens (HCO3/Cl exchange) -> net result is NaCl brought into the cell (water follows salt)

Question 8

Water molecules per ion

Answer 8

187 (56M H2O, 0.3M ions; 56/0.3=187)

Question 9

Essential Amino acids

Answer 9

Exchanged for non-essential amino acids (NEAA) which are established in high concentrations by Na/NEAA cotransporters and normal intracellular production

Question 10

Fatty acids

Answer 10

have transporters that increase their rates of membrane crossing

Question 11

Calcium

Answer 11

Na/Ca pump in most cells; Na/Ca exchanger in cells with high Ca flux; small Na change can make a big Ca change in exchanger