TRANSPORT ACROSS MEMBRANE

Question 1

TRANSPORT PROTEINS

Answer 1

CARRIERS = binding of transported molecukes on one side -> conformational change -> transport to the other side

CHANNELS = enable passage of transported molecules (ion channels)

Question 2

TRANSPORT MEDIATED BY CARRIERS

Answer 2

UNIPORT = transport of one type of molecule
-passive is facilitated / diffusion (GLUT1)
binds to molecule -> carrier changes conformation -> molecule is released
-active is ATPases (pumps)

SYMPORT = co transport of 2 types of molecules in the same direction
-passive is rare (frog stomach)
-active is glucose pump

ANTIPORT = co transport of 2 types of molecules in opposite directions
-passive is exchange diffusion (chloride bicarbonate exchanger, erytrocytes)
one molecule can go via
concentration gradient in if another molecule goes via
concentration gradient out
-active antiport is sodium potassium pump

Question 3

WHAT WAS THE FIRST ION DRIVEN PUMP TO HAVE IT STRUCTURE DETERMINED BY XRAY CRYSTALLISATION?

Answer 3

Ca2+ pump in sarcoplasmic reticulum

Question 4

AQUAPORINS

Answer 4

channels facilitating water diffusion across the membrane

Question 5

EXPLAIN THE TACTICS DIFFERENT CELLS USE TO AVOID OSMOTIC SWELLING

Answer 5

ANIMAL CELL = keeps intracellular solute concentration low by pumping ions out

PLANT CELL = cell wall is rigid and has turgidity

PROTOZOAN = periodically ejects water that moves into the cell

Question 6

TRANSPORT MEDIATED BY CHANNELS

Answer 6

LIGAND GATED ION CHANNELS = opening regulated by ligand binding
->intracellular or extracellular
-> neurotransmitters & intracellular signalling (IP3 and calcium in ER)

VOLTAGE GATED ION CHANNELS = opening is regulated by change of voltage on membrane
-> Na+ channel

STRESS GATED ION CHANNELS = opening is regulated by mechanical stress
essential for touch and hearing, coordination of muscle and regulation of blood pressure in veins and arteries

Question 7

ELECTROCHEMICAL GRADIENT

Answer 7

the sum of concentration gradient and membrane potential representing the driving force for ions to cross the membrane

Question 8

WHAT KIND OF MOLECULES CAN PASS THROUGH A SEMI PERMEABLE MEMBRANE VIA DIFFUSION?

Answer 8

small nonpolar ( O2, CO2, benzene)

small uncharged polar (H2O, glycerol, ethanol)

Question 9

WHAT COULD A DEFECT IN OSMOTIC PRESSURE IN HUMANS CAUSE?

Answer 9

lysis of erythrocytes
brain swelling

Question 10

OSMOTIC PRESSURE

Answer 10

pressure that needs to be applied to a solution to prevent the inward flow of water across a
semi permeable membrane, stabilizes concentration

Question 11

WHAT IS THE MEMBRANE UNDER PHYSIOLOGICAL CONDITIONS?

Answer 11

membrane is under physiological condition
polarized (30-100mV, negative charge inside, positive outside)