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MM Block 1 > Membrane Transport and Ion Channels > Flashcards

Membrane Transport and Ion Channels Flashcards

1
Q

Types of Transport across a cell membrane:

  3. 4.
A
  1. simple diffusion
  2. facilitated diffusion
  3. osmosis
  4. active transport
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2
Q

simple diffusion

  1. examples
  2. energy req’d?
  3. saturatable?
  4. Equation and Driving Force
A
  1. DMSO crossing a lipid membrane; small, uncharged molecules that don’t need channels/pumps
  2. No- molecules travel down conc. gradient
  3. no
  4. Ji (flux) = Pi (permeability of memb) * A (area of memb) * Ci (concentration gradient)
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3
Q

facilitated diffusion

  1. examples
  2. energy req’d?
  3. saturatable?
  4. Equation and Driving Force
A
  1. anything using a receptor/transporter to move down conc. gradient (ie: glucose carrier)
  2. No (moving down conc. gradient)
  3. Yes! Only have so many transporters
  4. Uncharged molecule: Ji (flux) = Pi (permeability of memb) * A (area of memb) * Ci (concentration gradient); **charged ion: **Ji (flux) = Pi (permeability of memb) * A (area of memb) * (61log(c1/c2) +Vm) ; this includes chemical and electrical gradients
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4
Q

Osmosis

  1. examples
  2. energy req’d?
  3. saturatable?
  4. Equation and Driving Force
A
  1. kidney reabsorbing water from urinary space into blood
  2. No
  3. Not really (maybe somewhat due to aquaporins?)
  4. J-h20 = L(p)*A*(deltaP-(sigmaRTC1-sigmaRTC2)) –> hydrostatic (delta P) and osmotic pressures (sigma RT(C1-C2))

sigma is the reflection coefficient: sigma = 1 for a completely impermeant solute and 0 for water

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5
Q

Active transport:

  1. Types
  2. examples
  3. energy req’d?
  4. saturatable?
  5. Equation and Driving Force
A
  1. primary: is an ATPase; 2ndary: uses a gradient made from a different ATPase
  2. ATPases, pumps, etc used to move large, charged molecules against conc gradient
  3. YES- moving against conc gradient
  4. Yes- only so many transporters
  5. Varies
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6
Q

electrogenic co-transporters

A

affect and affected by Vm (ie: ion channels, Na+/K+ ATPase, H+ ATPase)

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7
Q

electroneutral co-transporters

A

Do not affect or affected by Vm (solely concentraiton gradient). (e.g.. Na+/Cl- co-transporter, Na+, H+ antiporter

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8
Q

hydrostatic pressure

A

water moves preferrentially from high pressure to low pressure (e.g.: water in high-pressure artery moves outwards into surrounding tissue)

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9
Q

osmotic pressure

A

water will be drawn across a membrane to higher concentrations of solute in order to reach equilibrium, but only if the solute itself cannot move across the membrane first.

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10
Q

urea is hypotonic because

A

its large proteins move freely into the cell, drawing lots of water into the cell, causing it to swell

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11
Q

hypotonic fluids

A

have low tonicity relative to the cell, so water moves into the cell, making cells swell

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12
Q

hypertonic fluids

A

fluid has high tonicity relative to the cell, so water moves out of cell, causing cell shrinking

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13
Q

isotonic fluids

A

have same tonicity as teh cell, so water does not move one way or the other

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14
Q

____moves H20 across tissues

A

osmotic pressure by Na+ pumps and water channel aquaporins (create high permeability for water)

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15
Q

Nernst Equation:

Nernst equilibrium:

Nernst/Reversal Potential:

A

deltaMu (chemical and electrical potential put together) = 61*log(c1/c2) +Vm = 61*log(c1/c2) +zF(V)

Chemical and electrical gradients come to a standstill, so deltaMu =0 .

Vk = -61log(c1/c2), assuming only k crosses membrane

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16
Q

Goldman equation is used for______. It is a modified ____.

A

many ions at deltaMu =0. modified Nernst equation

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17
Q

Edema in legs:

A

Na+ retained, water follows, legs swell

18
Q

Flux = 0 when

A

deltaMu = 0 or permeability =0

19
Q

Why is the inside of a cell negative?

A
  1. Na+ K+ ATPase: 3 Na+ leave the cell and 2K+ come in, so change of -4mV per cycle
  2. K+ channels which transport K+ out of the cell because PK >PNa
  3. Cl channels: Inward gradient of Cl-
20
Q

To find Nernst potential for element i (Vi):

To find driving force on element i (deltaMu)

A

Z(Vi) = -61*log(c1/c2)

deltaMu = 61*log(c1/c2)+ zF(V)

21
Q

general structure of ion channels

A
  • large glycoprotein tubes
  • multiple protein subunits
  • hydrophobic AAs face lipid membrane, hydrophilic AAs face pore or intra/extracellular space
22
Q

can determine # of transmembrane passes an ion channel has by:

A

counting the # of hydrophobic regions

23
Q

Common functions of ion channels

A
  • action potentials
  • hormone release
  • cell motility
  • other FAST cellular processes (ion channels are one of the fastest modes of transport into/out of the cell
    *
24
Q

ohmic conductance

A

linear relationship between Vm and i (current)

25
Q

rectifying conductance

A

non-linear relation between Vm and i because channel is altered at different potentials; rectifying channels have a preference for direction of ion flow

26
Q

saturation of ion channels:

A

like traditional catalysts, ion channels are saturable and have a max speed

27
Q

determines ability of an ion to travel through a channel

A
  • size
  • ion charge
  • channel flexibility
28
Q

different kinds of ion channel gates (gating opens and closes the channel)

A
  • ligand binding (bound drug/molecule opens/closes channel)
  • phosphorylation (2nd messenger cascade)
  • pressure/stretch-gated (cytoskeleton regulation)
  • temperature gated

ligand, ball and chain, or structural changes in the channel

29
Q

Inactivation of the channel:

A

state in which no amount of depolarization of the membrane will open up the channel

  • prolonged exposure to necessary ligand causes desensitization
30
Q

Curare

A

reversible, competitive agonist of AcCh receptor (closes channel temporarily)

31
Q

BTx:

A

irreversible, non-competitive antagonist of ACh receptor (closes channel permanently)

32
Q

phenobarbital

A

keeps GABA channel open, more Cl- comes in –> sleepy time.

33
Q

PCP

A

blocks glutamate-activated channel

34
Q

trimeric ion channels

A

purinergic (sense intracellular ATP levels)

35
Q

quatrameric ion channels

A

glutamate-bindin

36
Q

pentameric ion channels

A

Ach, GABA, Serotonin, Glycine (all neurotransmitters)

37
Q

voltage-gated ion channels:

A

K+, Na+, Ca++ channels

38
Q

TRP ion channels:

A

cation non-specific, respond to mechanical force

39
Q

CLC ion channels

A

CL- permeable channels, gated by voltage, pH, and swelling

40
Q

problems that can occur w ion channels

A
  • mutations (as in cystic fibrosis)
  • abnormal expressions
  • autoimmune attack on the channels (as in myasthenia gravis, when antibodies attach AcCh receptors)

MM Block 1 (15 decks)

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