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ANAT458 > Membrane transport (lect 9, 12, 13) > Flashcards

Membrane transport (lect 9, 12, 13) Flashcards

1
Q

can charged molecules cross the bilayer?

A

no, even if they are small

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2
Q

what state of a membrane makes it impermeable?

A

gel state

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3
Q

what is hexadecane and what is it used for?

A

a very non-polar solvent used to measure the ability of a molecule to pass through the membrane, depending on if the molecule easily solubilizes or no

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4
Q

what type of molecule rapidly passively permeate through the bilayer?

A

gases (O2, N2), hydrocarbons with one or 2 hydroxyl groups (ethanol)

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5
Q

what type of molecule moderately passively permeate through the bilayer?

A

water, uncharged compounds (lactic acid)

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6
Q

what type of molecule slowly passively permeate through the bilayer?

A

ions, charged molecules, sugars

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7
Q

when does diffusion happen according to delta G?

A

when delta G is negative

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8
Q

what is the source of energy of primary active transport?

A

ATP

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9
Q

what is the source of energy for primary active transport? gives examples of carriers

A

hydrolysis of ATP (ATPases, ABC transporters)

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10
Q

what is the source of energy for secondary active transport? gives examples of carriers

A

the energy comes from the coupled movement of a second solute down its concentration gradient (sodium-glucose symport)

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11
Q

For a species I, equilibrium will be reached, not when concentrations of I on both sides become equal, but rather when _______________

A

the membrane potential becomes equal to the membrane potential at equilibrium

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12
Q

what type of carriers are valinomycin and gramicidin?

A

ionophores (carries a specific molecule across a membrane)

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13
Q

what is the Nernst equation for charged ions at equilibrium at 37 degrees?

A

membrane equilibrium potential = - (61.5 mV / Zi) log10 ( [I]b / [I]a )

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14
Q

what are the predictions associated with the GHK constant?

A
  • When permeability coefficient P for one ion greatly exceeds those for the others, the Dy(1→2) becomes equal to the equilibrium potential for that ionic species
  • If the permeability of the membrane to one ion increases while the permeability to another species remains constant, the membrane potential will shift toward the equilibrium potential for the first ionic species
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15
Q

give an example of the GHK constant happening in real life

A

nerve action potential: APMA-R and NMDA-R channels

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15
Q

what happens to the membrane potential during the first phase of signal transmission in a neuron?

A

depolarization: Na+ channels open, Na+ gets in, membrane potential shifts towards Na+ equilibrium potential (+40 mV)

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16
Q

what happens to the membrane potential during the second phase of signal transmission in a neuron?

A

repolarization: K+ channels open, K+ exits the cells, membrane potential shifts back towards K+ equilibrium potential (-70 mV)

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17
Q

difference between channel and carrier?

A

a carrier must undergo conformational change

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18
Q

give examples of carriers

A

GLUT 1 transporter, Ca2+ ATPase pump, Glucose/Na+ symport

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19
Q

give examples of channels

A

aquaporins, voltage/ligan/mechanically-grated channels

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20
Q

describe the structure of aquaporin

A

6 TM alpha-helices/functional monomers organized as homotetramers

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21
Q

how do aquaporins get their selectivity?

A

via an arginine (R) (+ charged) and aromatic residues selectivity filter of 2.8 angstrom wide

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22
Q

Selectivity filter prevents ions from passing through based on what?

A
  • size (2.8 angstrom)
  • charge: from the positively charged arginine
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23
Q

what is a hydrated radius

A

radius must consider that there are water molecules strongly attracted to it

24
Q

what are oriented water chains?

A

water molecules forming chains via a H+ sneaking through aquaporins

25
Q

what prevents the reorganization of H+ forming oriented water chains from forming?

A

the positive charge on the 2 asparagines of the NPA-loop in aquaporin

26
Q

what is vasopressin’s effect on aquaporin?

A

it maintains aquaporin-2 at the cell surface to increase reabsorption in the collecting duct to concentrate urine

27
Q

what does the rocker-switch transporter mechanism allow for?

A

specific transport of one type of molecule without accompanying leakage of other small molecules

28
Q

describe the GLUT1 transporter structure

A

12 TM-spanning alpha-helices with both N and C terminus in the cytoplasm

29
Q

give characteristics of GLUT1 carrier transport

A

conformational change, bidirectional, passive

30
Q

what is the goal of Na+/K+ ATPase transport?

A

it prevents osmotic entrance of water in cells to dilute Na+, which would cause cells to burst

31
Q

how many of each ion does the NA/K ATPase let pass?

A

3 Na+, 2 K+ in oposite directions

32
Q

what triggers the conformational changes of the Na/K ATPase?

A

phosphorylation and the hydrolysis of the phosphate

33
Q

what kind of carrier is the LeuT transporter?

A

secondary active carrier

34
Q

how does the Leu T transporter work?

A
  • uses the natural Na+ gradient as a driving force for leucine
  • 3 confromations: 1. Na+ binding sites facing outwards
    2. ions occluded
    3. binding site facing inwards
35
Q

what is the LeuT analogous to in human?

A

SERT sodium-dependent serotonin transporter

36
Q

what is special about LeuT hemi-helices 1 and 6?

A

they form a “smart hinge” allowing movement, shielded from TM hydrophobicity, and maintain interactions with both Na+ and Leu

37
Q

what are the restrictions for the “thin” (first) gate of LeuT to be able to close?

A
  • must bind 2 Na+ BEFORE leucine
  • leucine must also be bound (it triggers the conformation change)
38
Q

what is SERT? function?

A

sodium-dependent serotonin transporter;
it resequesters serotonin to terminate synaptic-transmission events at serotonergic synapses

39
Q

what kind of transporter is SERT?

A

serotonin / Na+ symport

40
Q

how do anti-depressants drugs like citalopram, paxil and cocaine work?

A

they maintain sert in a closed confirmation to block serotonin re-uptake

41
Q

what type of channel is KcsA K+ channel?

A

K+ voltage gated channel

42
Q

describe the structure of KcsA K+ channel

A

tetramer of 4 identical subunits + selectivity filter inside

43
Q

how many K+ interactin sites does KcsA K+ channel has? how many K+ can it fit?

A

4 interacting sites, but can only fit 2 K+ at a time because the other sites are occupied by H2O

44
Q

Selectivity filter of KcsA K+ channel is too narrow to allow what kind of K+ ion to pass through?

A

hydrated K+

45
Q

what molecules give K+ channels their selectivitY?

A

C=O groups

46
Q

why can’t Na2+ pass through K+ channels?

A

because Na2+ has a smaller radius than K+ and the C=O groups therefore can’t interact with it

47
Q

what residues serve as hinge for opening and closing of MthK-channel?

A

glycine

48
Q

how does the mammalian Kv1.2 voltage gated K+ channel open and closes?

A

helix 4 of the voltage-sensing domain moves upward towards extracytoplasmic side when depolarization, opening the channel.
It moves downward when repolarization, closing the channel

49
Q

what residues allow mammalian Kv1.2 K+ channel to sense the change in transmembrane potential?

A

4 + charged arginine, attracted to negative charge

50
Q

what is the voltage sensing domain in Nav-channels?

A

helix S4 containing multiple positively-charged residues

51
Q

where is situated the Nav-channel selectivity filter?

A

in the outer region of the pore

52
Q

how big is Nav channel selectivity filter?

A

bigger than Kv (Na passes through in a partly hydrated form, 2 or more water molecules) (but K with 2 water ions is too big to pass through)

53
Q

what type of channel is the Kir6.2 channel?

A

ligand-gated

54
Q

what promotes Kir6.2 ligand-gated K+ channel opening and closing?

A

ATP promotes closing, PIP2 opening

55
Q

what proteins does Kir6.2 interact with?

A

SUR1 and SUR2 (integral membrane proteins)

56
Q

how does ATP closes Kir6.2 channel?

A

by pulling away cytoplasmic domain from the PM

57
Q

what does SUR1 do?

A

keeps Kir6.2 K channel open by hydrolyzing ATP

58
Q
A

ANAT458 (10 decks)

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