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PSC2002 > PSC2002/L03 Membrane Transport II > Flashcards

PSC2002/L03 Membrane Transport II Flashcards

1
Q

Give 2 examples of P-type ATPases that phosphorylate themselves during pumping cycle.

A

Na+-K+ pumps
Ca2+ pumps in SR

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2
Q

Give 2 inhibitors of Na+-K+ pumps.

A

Ouabain (strophantus)
Cardiac glycosides from digitalis spp

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3
Q

Describe the structure of a Na+/K+ pump.

A

11 transmembrane domains
3 cation binding sites I, II, III
Actuator domain
Phosphorylation domain
Nucleotide domain
Ouabain extracellular domain

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4
Q

Describe why the Na+/K+ pump transports unequal numbers of ions.

A

2 K+ for 3 Na+
K+ ions larger
Na+ fits into domains more easily

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5
Q

Describe the mechanism of the Na+/K+ pump. (10)

A

Na+ enters channel
Conformational change moves N domain
N domain phosphorylates P domain (ATP hydrolysed)
Gate shut and open other side using energy
Na+ released
K+ enters and fills vacant pockets
Conformational change to release phosphate from P domain through actuator domain
Regenerated ATP binds N domain & energy used to open gate
K+ exits
Actuator domain resets and cycle repeats

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6
Q

What are the 5 phases of the Na+/K+ pump mechanism?

A

E1 -> E1Na -> E1-P -> E2-P -> E2K

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7
Q

What is the Gibs-Donnan effect?

A

Describes unequal distribution of permanent ions on either side of a membrane which occurs in presence of impermanent charged ions

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8
Q

Describe counteraction of the Gibbs-Donnan effect.

A

Negatively charged proteins & dissolved solutes hold onto positive ions in cell
= low water potential
Water enters cell
Na+/K+ ATPase lowers number of dissolved particles inside cell
Ouabain inhibited

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9
Q

Define secondary transporters. (3)

A

Use kinetic energy provided by electrochemical gradients
Transport one solute down a concentration gradient
Coupled to transport of another against concentration gradient

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10
Q

Define symporters/co-transporters.

A

Integral membrane proteins involved in transport of two or more molecules or ions in same direction
E.g., Na+/glucose transporter

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11
Q

Give 2 examples of symporters.

A

Amino acid transporter
Na+/phosphate transporter
Na/K/Cl transporter
Na+/HCO3 cotransporter
Cl-/K+ symporter

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12
Q

Define antiporters.

A

Integral membrane proteins involved in the transport of two or molecules or ions in opposite directions

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13
Q

Give an example of an antiporter.

A

Na+/H+ (NHE)
Na+/Ca2+ (NCX)

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14
Q

Describe ATP binding cassette transporters (ABC transporters).

A

Transport small molecules (can remove toxins)
Includes CFTR

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15
Q

Describe the structure of ABC transporters.

A

Two membrane spanning domains
Two nucleotide binding domains
R - regulatory domain

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16
Q

What defines the probability of ABC-transporter opening?

A

Presence of ATP in NBD and phosphorylation of R domain increases probability

17
Q

Give an example of an atypical ABC-transporter.

A

CFTR

18
Q

What is the difference between osmolarity and osmolality?

A

Osmolarity: total concentration of dissolved particles in a litre (osmol/L)
Osmolality: number of dissolved particles per unit mass (osmol/H2O)

19
Q

Define osmotic pressure.

A

Pressure exerted by flow of water across membrane
Determined by solutes concentrations

20
Q

Define tonicity.

A

Measure of the effect a solution has on cells placed in it and is driven by osmolarity

21
Q

What occurs to a cell in:
a) Hypotonic
b) hypertonic
c) isotonic solution?

A

a) cell expands
b) cell shrinks
c) no change

22
Q

What is the equation for Flux (flow)?

A

J = P./\C
J = flux
P = permeability
/\C = conc. difference

23
Q

What is the equation for permeability?

A

P = Dk/x
D = diffusion coeficient
k = partition constant
x = distance

24
Q

What is the equation for water flow?

A

Jv = Lp x /\P
Jv = water flow
Lp = hydraulic water pressure
/\P = pressure

25
Q

Give an alternative equation for water flow.

A

Jv = Lp x o x RT x /\C
o = solute reflection coefficient

26
Q

What is the membrane permeability to a compound if the solute reflection coefficient is:
a) 1
b) 0
c) 0.5?

A

a) Impermeable
b) Fully permeable
c) partially permeable

27
Q

Define pores.

A

Tiny transient gaps in the bilayer
Each pore contains around 10 water molecules in single file
One pore per 1000 lipid molecules

28
Q

Give 3 structures of aquaporins.

A

Hemipore 1
Hemipore 2
Hourglass

29
Q

Which 2 kinds of aquaporins are regulated?

A

AQ2
AQ3

PSC2002 (5 decks)

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