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51 Cards in this Set

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  • Back
Define Simple Diffusion of nonelectrolytes:
Passie movement thru a porous membrane of finite thickness W/OUT ANY HELP of carrier protein.
Only force that plays a role in simple diffusion:
Chemical potential gradient
Defining features of a nonelectrolyte:
-Electrically neutral
-May have charged end groups
-Not necessarily nonpolar
Lipid Soluble Nonelectrolytes:
-Respiratory gases O2, CO2, N2
-Organic alcohols & ketones
-Volatile anesthestics
How do lipid-soluble nonelectrolytes pass thru the bilayer?
They just passively diffuse
Lipid Insoluble Nonelectrolytes:
-other small organic molecules
How do Lipid Insoluble Nonelectrolytes pass thru the bilayer?
Via movement through pores
Why does H2O move at an exceptionally higher rate than other lipophobic nonelectrolytes?
B/c it can pass thru the bilayer in two ways:
-Simple diffusion
-Via aquaporins
What pushes water through aquaporins?
Osmosis or Hydrostatic pressure
2 Types of Aquaporin isoforms:
Aqp1 = in RBCs, Renal proximal tubule, Desc loop of henle, choroid plexus, and lots of other places
Aqp2 = in nephron collecting duct
What regulates Aquaporin 2?
Vasopressin (ADH)
Is aquaporin 2 a pore?
No - because it has open and closed states, therefore a channel by our definition.
How does ADH regulate AQP2?
By regulating its amt in the PM
What is the AQP structure like?
2 identical sets of 3 membrane spanning helices that altogether form the protein channel.
What residues make up the pore of AQP?
NPA - asparagus, pro, ala
-2 of these face each other
What law governs passive simple diffusion across the PM?
Fick's law of diffusion
What does Fick's law tell?
-Rate of passive diffusion of a NONELECTROLYTE solute across a membrane of FINITE thickness under the influence of a CHEMICAL gradient
Equation for Fick's law:
Qnet = ----------
What is D?
Diffusion coefficient = 1/MW
What does D tell you?
The smaller an ion or thing is, the higher the diffusion coefficient and faster rate.
What is A?
The cross sectional area of transport
What is B?
Beta - the partition coefficient
-C in membrane / C outside cell
-C in membrane / C inside cell
What is x?
X = the depth of the membrane being crossed
What does the partition coeffient tell?
The conc of substance outside relative to within the membrane (or inside relative to it).
How easily it enters membrane.
What eqn do you use if calculating rate of diffusion from inside to outside the membrane?
Q = --------
What is Q?
The number of particles that cross the membrane in a given amt of time.
How are B and D different?
B = ease of solute entry into the membrane.
D = ease of solute movement within the membrane.
What does a B > 1 mean?
Solvent enters the membrane easily and is lipophilic and hydrophobic.
What molecules typically have a B > 1?
What does a B = 1 mean?
The solute is equally soluble in membrane or aqueous phase.
What does a B < 1 mean?
The solute is more soluble in the aqueous phase than membrane; Lipophobic, hydrophilic
What things have a B < 1?
What energy is needed for
-B > 1 solutes
-B = 1 solutes
-B < 1 solutes
B > 1 spontaneously enter memb; energy actually given off.
B = 1 no energy required
B < 1 need energy to enter memb.
What is P?
A permeability constant that takes into account -DB/x and is predetermined for solutes.
What is Fick's law when you use the permeability constant?
Qnet = Pc A Ci - Co
What is flux?
J = # of particles crossing membrane in given unit of time per cross sectional area
-J = Q/A
How does Flux relate to Fick's law?
J = P x (Ci-Co) = Q/A
How are the Permeability constant and Partition coefficient related?
Directly proportional
Why do we use the permeability coefficient?
Because x, D and B can't be accurately measured for every membrane in biology.
What is passive transmembrane flux of ELECTROLYTES dependent on?
-Concentration gradient
-Electrical energy of solute
-NOT the help of a carrier protein
How do ions passively diffuse?
Through protein CHANNELs but they are not HELPED.
What determines an ion's flux when it is at chemical equilibrium inside/outside a cell?
The ion's potential energy on either side of the membrane.
If an ion's potential energy inside a cell is lower than outside, where will the ion go?
From outside into the cell - down its electrical gradient.
Equation for ion flux driven only by electrical potential:
Q = zPeA[C](Ei-Eo)
What's that again?
Q = zPEACE o' de world mon
Are ions typically at only electrical equilibrium and not chemical?
NO; Qnet = Qchem + Qelec
What is the case with ion flux in physiology?
Qelec and Qchem are at equilibrium and equal each other! Qnet = 0
What equation is used to calculate the equilibrium potential of an ion?
The nernst equation
Nernst Eqn:
E = -61 log--
How do you calculate the Ecl?
E = -61 log--
Even if you're unhappy chloride gets a lollipop
What happens if the permeability of a particular ion increases relative to other ions?
The resting Em will approach the Eion for that ion!