Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BIOC 303 > 3.2 Channels > Flashcards

3.2 Channels Flashcards

1
Q

characteristics of channel proteins

A
  • no binding site
  • transport downhill
  • usually for ions
  • selective but less stereospecific than carriers
  • can be gated or not
  • allows for very high movement rates
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

why is a Cl- channel needed for the acidification of the vesicle lumen?

A

As H+ is transported into the lysosome (makes it , Cl- is brought in from the cytosol to balance the membrane potential), and also combines with H+ to make HCl

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

valinomycin

A

ionophore, hydrophobic peptide

  • facilitates movement of potassium ions through lipid membranes down electrochemical gradient
  • carbonyls bind to K+ in hydrophilic cavity
  • hydrophobic AA coat outside
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

monensin

A

Na+ ionophore

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

how does osmosis work with solute concentration

A

water flows from low to high salt concentration (or you can think of as high salt concentration regions have low water concentration, so water flows there to establish water concentration equilibrium)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

why do we need a potassium channel

A
  • K+ very impermeable because of hydration shell with water
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

KcsA

A

K+ channel (transports K+ from exterior to cytosol)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

KcsA structure

A

four identical subunits (8 TM helices)
- cone-shaped channel with wide end towards extracellular space
-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

selectivity filter of KcsA

A

Channel path made of carbonyl oxygen of TVGYG

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how many K+ binding sites are there in K+ channel

A

4, but only 2 are occupied because they repel each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

how does the K+ move through the channel

A

1) repulsion of K+ ions

2) carbonyl oxygens of the TVGYG selectivity filter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

why is the selectivity filter selective for K+ over Na+

A

K+ fits better.

Na+ ion is too small for proper coordination with the carbonyl oxygens of the selectivity filter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how are the K+ attracted to the K+ channel

A

pore helix has a dipole moment that attracts the K+ anions to the cytosolic entrance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Aquaporin

A

transports water from extracell to cytoplasm through very narrow passageway

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Aquaporin structure

A

6 TMS helices and 2 half TMS helices which have 2 asparagine residue

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

why is aquaporin impermeable to H+ even though H+ is smaller than H2O

A

there are two asparagine residues at the two half TMS helices that forms hydrogen bond to the waters that prevents hydrogen hopping

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

explain hydrogen hopping?

A

protons can diffuse using hydrogen bonds to hop from one water molecule to another

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

how many hydrogen bonds can water make

A

4 maximum (1 with each of the two hydrogens, 2 with the oxygen lone pairs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

how is the aquaporin so selective

A

1) super narrow passageway
2) arginine residues (+) discourage cations from passing
3) 2 half helices orient so that the + dipoles point towards the center so that the water molecule reorients as it passes through the channel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

explain patch clamping

A

technique for investigating the opening, closing, and ion conductance of a membrane protein

1) patch of membrane with a channel is pulled from cell
2) depolarizing voltage applied
3) measure the flow of electric current to measure the channel activity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

explain planar lipid bilayers

A

technique for measuring the electrical properties of a bilayer

1) sheet of plastic with small hole separates two sides of a chamber
2) lipid bilayer formed across hole
3) electrodes on each side of the chamber and current applied
4) electrical properties are measured

22
Q

explain single channel recording of Kv

A

basically increase membrane depolarization and measure the current

  • increasing voltage increases:
    1) probability channel opens
    2) length channel stays open
    3) number of channels that open (multiple channels that open will “stacK” currents)
23
Q

Kv

A

Voltage-Gated K+ channel

  • similar to KcsA but has additional domains for sensing membrane potential
  • has TVGYG too
24
Q

describe the voltage-sensing paddles of Kv

A

each of the four paddles (S1-S4) has arginine

25
Q

describe the voltage-sensing paddles of Kv

A

each of the four paddles (S1-S4)

  • S4 have voltage-sensing Arg residue
  • depolarization leads to paddle moving from interior to exterior
  • S4 moves S5, which moves S6 and opens the pore
26
Q

why can’t K+ pass through Kv when it is closed

A

the S6 helices are too tightly bound

27
Q

Nav

A

Voltage-Gated Na+ channel

28
Q

Nav structure

A

very large and awkward, but main subunit (a) is essential
- large protein with 4 domains (6 TM each, so total 24 TM)
-

29
Q

describe the significance of helix 4, 5, and 6 of the 4 domains of the a subunit of Nav

A

Helix 4: voltage sensor (strongly +)
Helix 5/6: activation gate
long loop between helix 5 and 6 on the extracellular space side

30
Q

why is it so important to maintain a Na+ gradient where Na+ high outside?

A

1) drive transport (import) of nutrients during co-transport
2) propagation of nerve impulse

31
Q

how do the 4 positively charged TMS Helix 4 in Nav maintain the closed position

A

negatively charged membrane potential on the inside pulls the TMS inwards

32
Q

explain mechanism of Nav transport (5)

A

1) 4 positively charged TMS4 helices held together by negative charge
2) depolarization lessens pull and helix 4 relaxes on cytosolic side
3) Na+ goes through
4) channel-inactivating segment moves and inactivates channel (plug) on cytosolic side
5) repolarization of membrane, channel-inactivating segment displaces and the channel is closed again

33
Q

draw typical graph of actional potential with respective to membrane potential

A

slide 14

34
Q

why is the action potential so rapid?

A
  • self-amplification process

- opening of few Na+ channels depolarizes the membrane and then even more Na+ channels open

35
Q

how does the cell go back to resting value of -70 mV

A

1) K+ channel opens to restore the membrane potential
2) Na+ channel becomes inactivated
3) NaK ATPase!

36
Q

draw graph of action potential

A

but with Na+ permeability and K+ permeability in it as well

37
Q

describe activity of Nav and Kv in a neuron during resting state

A

both Nav and Kv in resting states
- extracell (+)
cytosol (-)

38
Q

describe activity of Nav and Kv in a neuron during depolarization

A

Nav opens and Na+ comes into cysol (self-amplification)
- -70mV to 50 mV
- extracell (-)
cytosol (+)

39
Q

describe activity of Nav and Kv in a neuron during repolarization

A

Nav becomes inactivated. K+ opens
- 50 mV to -71 mV
- extracell (+)
cytosol (-)

40
Q

describe activity of Nav and Kv in a neuron during repolarization

A

Nav closes. K+ still open and restores back to -70 mV

41
Q

what is the normal membrane potential across the PM

A

extracell (+)

cytosol (-)

42
Q

describe the positive feedback loop idea of the action potential

A
  • the membrane potential controls the state of the ions channels
  • but the ion channels can then control the membrane potential (increases even more)
43
Q

how come the action potential is able to move in one direction but not the other?

A

as the Na+ ions enter the cytosol, the excess diffuses in both directions and depolarizes the surrounding area too

  • however the Na+ upstream have just been inactivated so can’t be open so soon
  • the Na+ channel downstream can open!
44
Q

at the physiological level, how come action potentials move so fast along the axon?

A
  • Na+ channels are concentrated along nodes of Ranvier
  • the action potential can jump from node to node (excess Na+ will diffuse across and create a depolarizing effect in the next node)
45
Q

describe the action potential effect at the postsynaptic cleft

A

1) when wave of depolarization reaches the axon tip, voltage gated Ca2+ channels open and Ca2+ enters cytosol
2) rapid increase of internal [Ca2+] triggers exocytic release of acetylcholine
3) acetylcholine binds to receptors of (other side) postsynaptic neuron (ligand-gated channel) and causes the ion channel to open
4) extracellular Na+ and Ca2+ enter through the channel
5) depolarizes next axon

46
Q

nAchR

A

acetylcholine receptor, ligand-gated ion channel of skeletal muscle

47
Q

how does muscle contraction work

A

1) acetylcholine released into synaptic cleft binds to nAchR (acetylcholine receptor ion channel)
2) opens up acetylcholine receptor ion channel and Na+ and Ca2+ enter postsynaptic neuron
3) rapid influx of Ca2+ triggers opening of Ca2+ release channel at the sarcoplasmic reticulum
4) increase of cytosolic [Ca2+] causes myofibrils to contract

48
Q

nAchR structure

A

acetylcholine receptor

- 5 subunits with 4 TM helices (M1-3 hydrophobic, M2 amphipathic and faces inside of the “pore”)

49
Q

closed structure of nAchR

A

bulky hydrophobic Leu side chains of M2 close channel (face inside of pore)

50
Q

how does nAchR open?

A

1) binding of 2 acetylcholine
2) M2 helices twist
3) Leu residues turn away and hydrophilic (polar) residues line the channel)
4) Na+ and other ions can now pass through

51
Q

Katp

A

nucleotide-gated potassium channel

  • bound to ATP = closed
  • not bound to ATP = channel opens and K+ exported
  • made of Kir channel + sulfonylurea receptor
52
Q

how does skin sense temperature

A

Thermo-TRP channels

BIOC 303 (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions