Phys:membrane Transport 1-2

Front 1

What's the problem with diffusion?

Back 1

It's good over short distances but very slow over long distances.

Front 2

Convection: defn

Back 2

Bulk movement of fluids

Front 3

Benefits/consequences of facilitated diffusion

Back 3

1) Allows passage of something that normally wouldn't passively diffuse
2) Imparts specificity
3) Shows saturation/reaches some transport maximum
4) Shows competitive inhibition (related substrates can also bind)

Front 4

Transport constant, Km: defn

Back 4

Concentration at which you get 1/2 maximum transport

Front 5

Characteristics of channels for passive diffusion of ions

Back 5

1) Specific
2) Gated: sometimes open

Front 6

Ways of gating channels

Back 6

1) Electrical potential - voltage gated

2) Ligand gated - something binds and causes it to changes concentration

Front 7

Equilibrium potential: Defn

Back 7

Potential at which the diffusive flow is exactly balanced

Front 8

Osmotic pressure

Back 8

the pressure that exactly stops osmotic flow

Front 9

Van't Hoff equation

Back 9

pi = NRT
(just a form of ideal gas law)

Front 10

Osmotic coefficient

Back 10

The Van't Hoff eqn. is not exact for physiological solutions. Must correct by multiplying Van't Hoff eqn. by the osmotic coefficient, φ.

π = RTφ_iC_i

Front 11

Osmolarity vs. Tonicity

Back 11

Osmolarity (or osmotic pressure) is a property of a "solution," for example, 0.9% NaCl, or 1.8% urea, or plasma, or the cytoplasm of a cell. Osmolarity is independent of the properties of membranes.

Tonicity is defined for a particular set of solutions and a particular cell. Tonicity depends on (1) the osmolarity of both the intracellular and extracellular solutions and (2) the properties of a particular membrane represented by its reflection coefficient.

Front 12

What ion is a cofactor in the activation of the Na+/K+/ATPase pump?

Back 12

Mg²⁺

Front 13

Electrogenic: defn

Back 13

Separates charges and contributes to the membrane potential.

Ex. The Na+/K+/ATPase pump takes out 3 Na+ ions and brings in 2 K+, thus leading to the inside of the cell being more negatively charged than the outside.

Front 14

Fick's 1st law of diffusion

Back 14

J = -D (ΔC / Δx)

J = flux; D = diffusion coeff; ΔC = Concentration difference; Δx = distance separating two concentrations.

Front 15

What inreases the diffusion coeff? What decreases it?
What are the implications of these things?

Back 15

D increases with increasing Temp.

D decreases (inversely proportional) with increasing radius of the particle and viscosity.

Implications: The hotter something is the faster it diffuses. The bigger and more viscous something is the slower it diffuses.

Front 16

Partition coefficient: defn and formula

Back 16

Defn: Ratio of equilibrium concentrations in lipid and aqueous phases.

K_s = equilibriumC_lipid / equilibriumC_water

Front 17

Equation relating passive flux, permeability, and concentration

Back 17

J = pΔC

p = permeability (cm/s)

Front 18

What inreases the permeability coeff? What decreases it?
What are the implications of these things?

Back 18

p = D_lipidK_s / δ

Permeability increases in proportion to diffusion coeff in lipid phase,D_lipid, and partition coeff K_s

Front 19

What type of diffusion saturates with increasing [solute]?

Back 19

Facilitated

Front 20

What type of diffusion is specific and shows competitive inhibition?

Back 20

Facilitated

Front 21

Equation for the current carried by a protein channel

Back 21

Analog of Ohm's law:

I = E/R
E = voltage driving current
R = resistance
I = current

Amps = volts/ohms

Front 22

Which type of transport couples uphill movement of one solute with downhill movement of another?

Back 22

Secondary active (no ATP needed)

Front 23

The Na⁺ - Ca²⁺ exchange (NCX) is an example of what type of transport?

Back 23

Secondary active transport (antiport).

Transports Ca²⁺ out of cell (low to high concentration) by letting 3 Na⁺ ions into cell (from hi to low concentration)

Front 24

Antiport: defn

Back 24

Type of 2ndary Active Transporter that moves two solutes in opposite directions. (in/out)

Front 25

Symport: defn

Back 25

Type of 2ndary Active Transporter that moves two solutes in the same direction. (in/in).

AKA cotransporters.

Front 26

Osmolarity: defn

Back 26

Concentration of osmotically active solute particles.

Front 27

What is the osmolarity of a 2M NaCl solution?

Back 27

4M. Must take into account that NaCl dissociates into two ions.

Front 28

Eqn. relating Force, time, and momentum

Back 28

F = ΔP / Δt

Force = change in momentum / change in time

Front 29

Eqn relating Pressure, Force, and Area

Back 29

F = P/A
Force = Pressure / Area

Front 30

What correction is made when the membrane is slightly permeable to solutes?

Back 30

Must multiply by reflection coefficient, σ

π = RTφσC

Front 31

What is σ when the membrane is impermeable to solute?

Back 31

1

Front 32

Colligative properties: Defn.

Back 32

Properties that come about by dissolving solutes in solution. They're really all the same.

Ex. Freezing point depression; boiling point elevation; vapor pressure depression

Front 33

Equation relating fluid flow across a membrane and osmosis

Back 33

Qv = A L_p [ΔP - σΔπ]