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Biochemistry 304 > CH 13 Membrane Channels and Pumps P1 > Flashcards

CH 13 Membrane Channels and Pumps P1 Flashcards

1
Q

Membranes are made permeable to specific molecules in the presence of three classes of transporters:

A

ATP-driven pumps
carriers
channels

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2
Q

Lipophilic / Hydrophobic Molecules

A

pass directly through phospholipid bilayers down [gradient]

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3
Q

Polar / Fully Charged Molecules

A

req. channel to move across membrane down [gradient]

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4
Q

Simple diffusion

A

doesn’t req. E or membrane proteins

[high] to [low]

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5
Q

Facilitated Diffusion / Passive Transport

A

polar / fully charged molecules that req. presence of channel to move across a cell down [gradient]

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6
Q

Active Transport

A

moves molecules across membrane against [gradient].

req’s E

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7
Q

E-rich Situation

A

unequal distribution of uncharged molecule across membrane

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8
Q

Gibb’s Free E Eqn

A 
dG = RT ln (c2/c1)
R: gas constant
T: temp K
c1: [side] 1
c2: [side] 2
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9
Q

Gibb’s Free E

A

Free E req’d to move solute from one side of a membrane at [c1] to the other at [c2]

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10
Q

Un= distribution of a charged molecule has?

A

electrical potential

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11
Q

Electrochemical / Membrane Potential

A

concentration diff’s and charge diff’s taken into account for un= distribution of charged molecule w/ electrical potential

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12
Q

Electrochemical / Membrane Potential Eqn

A

dG = RT ln (c1/c2) +ZFdV
Z: charge of molecule
dV: voltage across membrane
F: Faraday constant

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13
Q

Most animal cells have ____ K+ and ____ Na+ relative to the environment.

A

high [K+]

low [Na+]

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14
Q

Na+K+ Pump

A

req’s action of active transport system to gen and maintain membrane potential

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15
Q

Na+K+ ATPase

A

P-type ATPases
phosphorylated aspartate intermediate
Na+K+ Pump

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16
Q

P-Types ATPases Couple ____ and ____ to pump ____ across membranes.

A

phosphorylation
conformational changes
calcium ions

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17
Q

Pumps exist in what 2 conformations?

A

ion binding site facing into cell and facing out of cell

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18
Q

ATP Hydrolysis

A

powers interconversion of 2 conformation

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19
Q

Sarcoplasmic Reticulum Ca2+ ATPase (SERCA)

A

P-Type ATPase
pumps Ca2+ from muscle cytoplasm to sarcoplasmic reticulum.
enzyme.
calcium pumping.

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20
Q

SERCA Structure

A

single polypeptide chain

transmembrane domain - 10 alpha helices

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21
Q

SERCA Function

A

binds Ca2+

22
Q

SERCA Cytoplasmic Portion

A

3 Domains:
N domain
P domain
A domain

23
Q

SERCA N domain

24
Q

SERCA P domain

A

accepts P during rxn cycle

Asp 351 binds P

25
Q

SERCA A domain

A

links N and P domains

26
Q

Catalytic / Transport Cycle

A
  1. bind cytoplasmic Ca2+
  2. N domain binds ATP
  3. P transferred to Asp in P domain
  4. ADP released, structural change, Ca2+ binding site faces SR lumen, Ca2+ leaves enzyme
  5. P group in P domain hydrolyzed
  6. enzyme changes conf. Ca2+ binding site faces cytoplasm
27
Q

Digitalis

A

inhibits Na+K+ pump by blocking dephosphorylation

28
Q

Cardiotonic Steroids

A

found in foxglove.
inhibits Na+K+ ATPase
treats congestive heart failure.

29
Q

Cardiotonic Steroids: Digitoxigenin and Ouabain

A

members of class of inhibitors

30
Q

Digitalis decreases the ____ which results in ____.

A

Na+ gradient.

slower Ca2+ removal from cell.

31
Q

Digitalis increases the ____ which results in ____.

A

cellular Ca2+.

enhances contractile ability of heart.

32
Q

The human genome contains 70 genes that encode?

A

P-type ATPases

33
Q

P-Type ATPases transport

A 
H+
Ca2+
Na+
Cu2+
phospholipids w/ charged head groups
34
Q

All P-Type ATPases have the same fundamental rxn mech:

A

take advantage of free E release associated w/ ATP hydrolysis to drive membrane transport via conformational changes induced by addition / removal of phosphoryl group at key Asp site.

35
Q

Multidrug Resistance Protein

A 
membrane pump.
ATP-dependent pump.
extrudes small molecules from cell.
member of family - ABC transporters.
single polypeptide chain w/ 4 domains.
36
Q

ABC transporters are characterized by a common domain called?

A

ATP-binding cassette (ABC)

37
Q

ABC transporters consist of 2 ____ and 2 ____.

A

ABC domains

membrane-spanning domains

38
Q

Reaction Cycle of Multidrug Resistance

A
  1. channel open to cytoplasm
  2. substrate binds - conf. changes in ABC domain.
  3. ATP binds to ABC domains - structural changes orient substrate to face outside of cell.
  4. outward facing conf. to transporter reduced affinity to substrate - allows release.
  5. ATP hydrolysis - resets transporter to initial state.
39
Q

Lactose Permease

A

from E.coli.
symporter.
uses H+ gradient to power lactose into cell.

40
Q

Secondary Transporters / Cotransporters

A

use E of one gradient to power formation of another

41
Q

Symporters

A

power transport of molecule against [gradient].
couples movement of another molecule down [gradient].
both molecules move in same direction.

42
Q

Antiporters

A

use 1 [gradient] to power formation of another.

molecules move in opp directions.

43
Q

Uniporters

A

transport molecule in either direction.

depend on [difference] across membrane

44
Q

Lactose Permease Mech

A
  1. lactose-binding pocket faces outside of cell.
  2. H+ binds, lactose binds.
  3. permease everts.
  4. lactose leaves permease, enters cell.
  5. H+ leaves permease, enters cell.
  6. permease everts - cycle complete
45
Q

Ion Channels

A

rapid movement of ions across membranes down [gradient]

46
Q

Neuron Interior

A

higher [K+]
lower {Na+]
membrane potential -60mV

47
Q

Nerve Impulse / Action Potential

A

gen’d when membrane potential depolarized beyond critical threshold value.

48
Q

Action Potentials are the result of?

A

K+ channels and Na+ channels opening / closing in response to changes in membrane potential

49
Q

Patch-Clamp Technique

A

pipette placed against small portion of cell membrane.

reveals activities of single channels.

50
Q

Patch-Clamp uses Gigaseal which is?

A

suction applied to form tight seal btw pipette - plasma membrane.
measures channel activity when voltage applied across cell membrane.

Biochemistry 304 (14 decks)

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