Membrane Transport

Question 1

Total Body Water of a 70kg human and the divisions

Answer 1

TBW = 42L
Plasma = 3 L
Interstitial = 13 L
Intracellular = 25L (majority)

Question 2

Relative concentrations of Na+, K+ and Cl- across membrane

Answer 2

Na+ has greater EXTRACELLULAR conc, gradient leads in
K+ has greater INTRACELLULAR conc, gradient leads out
Cl- has greater EXTRACELLULAR conc, gradient leads in

Question 3

what is the fraction of blood made up of red cells called

Answer 3

hematocrit

Question 3

what does the concentration gradient of charged particles lead to

Answer 3

an electrochemical gradient

Question 4

why do plasma proteins affect solute distribution between plasma and interstitial fluid

Answer 4

because of the volume they occupy and the charge they carry

Question 5

what are the 5 ways in which small molecules can cross cell membranes

Answer 5

passive diffusion
aqueous diffusion
facilitated diffusion
active transport
endocytosis

Question 6

what type of molecules can pass directly through a membrane by passive diffusion

Answer 6

lipophilic molecules (e.g. steroids)

Question 7

what type of proteins form aqueous pores that facilitate diffusion

Answer 7

aquaporins

Question 8

passive vs aqueous diffusion

Answer 8

passive does not require a vehicle
aqueous is a molecules that cannot pass through the membrane but their conc gradient allows them to enter the cell

Question 9

what causes the conformational change in facilitated diffusion

Answer 9

chemical reaction (binding) between molecule and carrier protein

Question 10

why doesn’t facilitated diffusion require energy

Answer 10

net 0 change in energy because the conformational change causes a downhill movement down a concentration gradient

Question 11

what are the two types of active transport

Answer 11

primary active transport: hydrolysis of ATP
secondary active transport:
coupling movement of an uphill movement to a downhill movement

Question 12

what determines the flux of a given charged solute

Answer 12

the electrochemical potential energy difference

Question 13

which two types of transport are subject to Michaelis - Menten kinetics

Answer 13

facilitated diffusion and active transport as they involve a finite number of proteins so can be saturated and plateau

Question 14

how to determine the electrochemical potential energy difference for a molecule carrying a charge

Answer 14

chemical potential energy difference + electrical potential energy difference

Question 15

what determines the driving force of a charged solute across a membrane

Answer 15

electrochemical potential energy difference

Question 16

when is flux 0

Answer 16

in a state of equilibrium (at equilibrium potential / Ek)

Question 17

how to calculate the Ex of an ion

Answer 17

61.5log10[X]o/[X]i

Question 18

how to calculate the driving force of a charged particle

Answer 18

(membrane voltage) - Ex
positive is outward and negative is inward

Question 19

what is the equilibrium potential of a charged particle

Answer 19

potential at which there is not net movement of a given ion

Question 20

when to use Fick’s Law

Answer 20

to determine the flux of an electrically neutral solute

Question 21

how does the pKa and local pH affect the pharmacology of a drug

Answer 21

pKa = pH at which 50% of drug is ionised
unionised form can permeate the membrane
If a drug is ionised it will carry a hydration shell and be prevented from crossing the membrane

Question 22

what are the principal sites of carrier mediated transport

Answer 22

blood brain barrier
gastrointestinal tract
placenta
renal tubule
biliary tract

Question 22

what is the blood brain barrier

Answer 22

protective barrier of endothelial cells and capillaries which must be crossed to enter the brain. Prevents toxins entering the CNS

Question 23

how do hydrophilic molecules bypass the blood brain barrier

Answer 23

must use active transport or carriers
e.g. amino acids

Question 23

which two transporters are responsible for facilitated diffusion of fructose and glucose in the gut

Answer 23

GLUT2 and GLUT5

Question 24

what is responsible for establishing sodium and potassium gradients

Answer 24

Na+/K+ ATPase

Question 25

what are the different subunits of Na+/K+ ATPase

Answer 25

alpha - catalytic, binding sites
beta - regulatory, glycosylated