Lecture 2: physiological functions of transporters

Question 1

what is meant by osmotic pressure?

Answer 1

pressure generated when two compartments separated by membranes permeable to water contain different solute concentrations

Question 2

what is the difference between osmolarity and osmolality?

Answer 2

osmolarity = the number of osmoles of solute per 1L solvent
osmolality = number of osmoles of solute per 1KG of solvent

Question 3

what is meant by tonicity?

Answer 3

sum of the concentrations of the solutes which have the capacity to exert an osmotic force across the membrane

Question 4

what occurs when a cell becomes hypotonic?

Answer 4

regulatory volume decreases, loss of KCl

Question 5

what occurs when a cell becomes hypertonic?

Answer 5

regulatory volume increases, uptake of NaCl

Question 6

what is the role of the Na/H exchanger?

Answer 6

• exchanges extracellular Na for intracellular H

- alkalysing cytoplasm

Question 7

what is the role of the anion exchanger?

Answer 7

• exchanges extracellular Cl for intracellular HCO3

- acidifies cytoplasm

Question 8

describe the function of Plasma membrane Ca-ATPase and sacro/endoplamsic reticulum ATPase

Answer 8

• remove residual calcium

- both have high Ca2+ affinity and low capacity

Question 9

describe the function of the Na-Ca exchanger

Answer 9

• removes the most calcium
• low affinity for Ca2+ but high capacity
• electrogenic
• activity is membrane potential dependent

Question 10

what is meant by electrogenic?

Answer 10

producing a change in the electric potential of a cell

Question 11

describe the function of Mitochondrial Ca2+ uniporters

Answer 11

• buffers potentially damaging Ca2+
• operates at high [Ca]
• facilitated diffusion driven by mitochondrial membrane potential

Question 12

name the acid extruders

Answer 12

Na/H exchanger

Na+-bicarbonate-chloride transporter

Question 13

which pumps are utilised for the control of cellular [Ca2+] and are powered by primary active transport?

Answer 13

PMCA + SERCA

Question 14

what is the function of PMCA?

Answer 14

removes intracellular Ca2+

Question 15

what is the function of SERCA?

Answer 15

moves cellular Ca2+ into the ER

Question 16

which methods of cellular calcium control utilise secondary active transport?

Answer 16

• Na+-Ca2+ exchanger

- Mitochondrial calcium uniporter

Question 17

aside from SERCA, PMCA, NCX and the mitochondrial calcium uniporter, which other pumps/channels are involved in the control of cellular [Ca2+]?

Answer 17

• ligand gated Ca2+ channels
• voltage gated Ca2+ channels
• MNCX
• ER release channels