8. Passive Transport

Front 1

Define Simple Diffusion of nonelectrolytes:

Back 1

Passie movement thru a porous membrane of finite thickness W/OUT ANY HELP of carrier protein.

Front 2

Only force that plays a role in simple diffusion:

Back 2

Chemical potential gradient

Front 3

Defining features of a nonelectrolyte:

Back 3

-Electrically neutral
-May have charged end groups
-Not necessarily nonpolar

Front 4

Lipid Soluble Nonelectrolytes:

Back 4

-Respiratory gases O2, CO2, N2
-Organic alcohols & ketones
-Volatile anesthestics

Front 5

How do lipid-soluble nonelectrolytes pass thru the bilayer?

Back 5

They just passively diffuse

Front 6

Lipid Insoluble Nonelectrolytes:

Back 6

-Water
-Urea
-Glycerol
-other small organic molecules

Front 7

How do Lipid Insoluble Nonelectrolytes pass thru the bilayer?

Back 7

Via movement through pores

Front 8

Why does H2O move at an exceptionally higher rate than other lipophobic nonelectrolytes?

Back 8

B/c it can pass thru the bilayer in two ways:
-Simple diffusion
-Via aquaporins

Front 9

What pushes water through aquaporins?

Back 9

Osmosis or Hydrostatic pressure

Front 10

2 Types of Aquaporin isoforms:

Back 10

Aqp1 = in RBCs, Renal proximal tubule, Desc loop of henle, choroid plexus, and lots of other places
Aqp2 = in nephron collecting duct

Front 11

What regulates Aquaporin 2?

Back 11

Vasopressin (ADH)

Front 12

Is aquaporin 2 a pore?

Back 12

No - because it has open and closed states, therefore a channel by our definition.

Front 13

How does ADH regulate AQP2?

Back 13

By regulating its amt in the PM

Front 14

What is the AQP structure like?

Back 14

2 identical sets of 3 membrane spanning helices that altogether form the protein channel.

Front 15

What residues make up the pore of AQP?

Back 15

NPA - asparagus, pro, ala
-2 of these face each other

Front 16

What law governs passive simple diffusion across the PM?

Back 16

Fick's law of diffusion

Front 17

What does Fick's law tell?

Back 17

-Rate of passive diffusion of a NONELECTROLYTE solute across a membrane of FINITE thickness under the influence of a CHEMICAL gradient

Front 18

Equation for Fick's law:

Back 18

-DAB(Ci-Co)
Qnet = ----------
x

Front 19

What is D?

Back 19

Diffusion coefficient = 1/MW

Front 20

What does D tell you?

Back 20

The smaller an ion or thing is, the higher the diffusion coefficient and faster rate.

Front 21

What is A?

Back 21

The cross sectional area of transport

Front 22

What is B?

Back 22

Beta - the partition coefficient
-C in membrane / C outside cell
-C in membrane / C inside cell

Front 23

What is x?

Back 23

X = the depth of the membrane being crossed

Front 24

What does the partition coeffient tell?

Back 24

The conc of substance outside relative to within the membrane (or inside relative to it).
How easily it enters membrane.

Front 25

What eqn do you use if calculating rate of diffusion from inside to outside the membrane?

Back 25

-DAB(Ci)
Q = --------
x

Front 26

What is Q?

Back 26

The number of particles that cross the membrane in a given amt of time.

Front 27

How are B and D different?

Back 27

B = ease of solute entry into the membrane.
D = ease of solute movement within the membrane.

Front 28

What does a B > 1 mean?

Back 28

Solvent enters the membrane easily and is lipophilic and hydrophobic.

Front 29

What molecules typically have a B > 1?

Back 29

Lipids
Phospholipids
Sterols

Front 30

What does a B = 1 mean?

Back 30

The solute is equally soluble in membrane or aqueous phase.

Front 31

What does a B < 1 mean?

Back 31

The solute is more soluble in the aqueous phase than membrane; Lipophobic, hydrophilic

Front 32

What things have a B < 1?

Back 32

Ions
Urea

Front 33

What energy is needed for
-B > 1 solutes
-B = 1 solutes
-B < 1 solutes

Back 33

B > 1 spontaneously enter memb; energy actually given off.
B = 1 no energy required
B < 1 need energy to enter memb.

Front 34

What is P?

Back 34

A permeability constant that takes into account -DB/x and is predetermined for solutes.

Front 35

What is Fick's law when you use the permeability constant?

Back 35

Qnet = Pc A Ci - Co

Front 36

What is flux?

Back 36

J = # of particles crossing membrane in given unit of time per cross sectional area
-J = Q/A

Front 37

How does Flux relate to Fick's law?

Back 37

J = P x (Ci-Co) = Q/A

Front 38

How are the Permeability constant and Partition coefficient related?

Back 38

Directly proportional

Front 39

Why do we use the permeability coefficient?

Back 39

Because x, D and B can't be accurately measured for every membrane in biology.

Front 40

What is passive transmembrane flux of ELECTROLYTES dependent on?

Back 40

-Concentration gradient
-Electrical energy of solute
-NOT the help of a carrier protein

Front 41

How do ions passively diffuse?

Back 41

Through protein CHANNELs but they are not HELPED.

Front 42

What determines an ion's flux when it is at chemical equilibrium inside/outside a cell?

Back 42

The ion's potential energy on either side of the membrane.

Front 43

If an ion's potential energy inside a cell is lower than outside, where will the ion go?

Back 43

From outside into the cell - down its electrical gradient.

Front 44

Equation for ion flux driven only by electrical potential:

Back 44

Q = zPeA[C](Ei-Eo)

Front 45

What's that again?

Back 45

Q = zPEACE o' de world mon

Front 46

Are ions typically at only electrical equilibrium and not chemical?

Back 46

NO; Qnet = Qchem + Qelec

Front 47

What is the case with ion flux in physiology?

Back 47

Qelec and Qchem are at equilibrium and equal each other! Qnet = 0

Front 48

What equation is used to calculate the equilibrium potential of an ion?

Back 48

The nernst equation

Front 49

Nernst Eqn:

Back 49

Ci
E = -61 log--
Co

Front 50

How do you calculate the Ecl?

Back 50

Co
E = -61 log--
Ci
Even if you're unhappy chloride gets a lollipop

Front 51

What happens if the permeability of a particular ion increases relative to other ions?

Back 51

The resting Em will approach the Eion for that ion!