ILA 12 Diffusion and Osmosis

Question 1

What is diffusion?

Answer 1

the random movement of atoms and molecules, powered by thermal energy

Question 2

Diffusion is most efficient in long or short distances?

Answer 2

Short Distances

Question 3

What is the driving force for the diffusion of uncharged solutes across a membrane?

Answer 3

Concentration difference (gradient)

Question 4

What is the equation for net transport?

Answer 4

Net transport = PA([C1]-[C2])
P=permeability coefficient
A=area of the membrane

Question 5

What is used as the standard measure of hydrophobicity?

Answer 5

octanol:water partition coefficient (Kow)

Question 6

How is the octanol:water partition coefficent determined?

Answer 6

• by dissolving the compound in a 1:1 mixture of n-octanol and water
• Octanol and water spontaneously separate into upper (mainly octanol) and lower (mainly water) phases
• Kow = [Concentration in Octanol]/[Concentration in H2O]

Question 7

A compound with a high Kow means what?

Answer 7

very hydrophobic

Question 8

A compound with a low Kow means what?

Answer 8

very hydrophilic

Question 9

Equilibrium is reached faster with compounds that have a (higher or lower) Kow?

Answer 9

Higher

Question 10

What is Overton’s rule?

Answer 10

• describes the relationship b/w passive membrane permeability and hydrophobicity
• P = Kow/(MW)^(1/2)
• for compounds of the same MW, pemeability is directly proportional to Kow
• permeability is also inversely proportional to the square root of the molecular weight

Question 11

How does pH affect lipid solubility?

Answer 11

adding a net charge to an otherwise hydrophobic molecule drastically lowers its lipid solubility

Question 12

Diffusion of weak acids and bases across the cell membrane is dependent upon what?

Answer 12

Whether they are charged or uncharged

uncharged moves across, but charged does not

Question 13

What is the exception to the rule that charged molecules do not diffuse rapidly across lipid bilayers?

Answer 13

in the charge is delocalized then it can

Example: 2,4-DNP that alternates b/w charge/uncharged to cross membranes

Question 14

What is the main pathway for water transport across membranes?

Answer 14

water channels (aquaporins)

Question 15

What was the first aquaporin discovered?

Answer 15

AQP1

Question 16

What drives the net transport of water across membranes?

through aquaporins

Answer 16

Osmosis

Question 17

Describe osmosis

Answer 17

water flows to areas of higher solute concentration

think: if cooking and its to salty, you add h2o

Question 18

What is the red blood cell osmotic fragility test?

Answer 18

• Red blood cell osmotic fragility is measured by varying the osmolality of the medium and measuring the percent lysis
• If the [NaCl] outside the cell is lowered, the cell swells b/c of the inward osmotic force ([solute] higher in the cell)

Question 19

What is osmolarity?

Answer 19

the number of osmoles per liter of solution

Question 20

What is an isosmotic solution?

Answer 20

one that has the same osmolality as normal human plasma (275-299 mOsm/kg)

0.9% NaCl solution

Question 20

What is an isosmotic solution?

Answer 20

one that has the same osmolality as normal human plasma (275-299 mOsm/kg)

0.9% NaCl solution

Question 21

What is a hyperosmotic solution?

Answer 21

has osmolality higher than 299 mOsm/kg

Question 22

What is a hyposmotic solution?

Answer 22

has osmolality lower than 275 mOsm/kg

Question 23

How do you calculate serum osmolality?

Answer 23

=2([Na]+[K]) +[glucose] + [urea]

all in mM

Question 24

What is an osmol gap?

Answer 24

When there is a larger difference between calculated and measured osmolality of serum/plasma

caused by abn high levels of ethanol, methanol, ethylene glycol & others

Question 25

How is the stool osmotic gap calculated?

Answer 25

= 290 - 2([Na] + [K])