Lecture 19 - Txpt II Flashcards Preview

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Flashcards in Lecture 19 - Txpt II Deck (31)
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1
Q

Compare ion channel speed to ion pump speed

A

Channel 1000x > than pump

2
Q

The opening and closing of ion channels are responsible/shape the membrane _____.

A

Potential (flow down [gradient] changes electrical potential)

3
Q

Voltage gated ion channels respond to _____.

A

changes to membrane potential

4
Q

Chemically/ligand gated channels respond to _______.

A

ligands (or “signals”) binding to them.

5
Q

Mechanically gated channels respond to _____.

A

mechanical forces that deform them (P, Temp, pain, etc).

6
Q

Describe the “patch clamp” method of channel isolation.

A

A small (1 micron) pipette is placed against a cell’s plasma membrane. Depending on the amount of suction applied, either the entire cell (low suction) is removed, or just a portion of the membrane with embedded channels is torn away (high suction).

7
Q

Explain how homology of a protein sequence across species indicates the importance of said protein.

A

If a protein is homologous, it is a highly conserved protein, and therefore highly important to cell function. There is homology among sodium channels, potassium channels, etc.

8
Q

Describe the mechanism of “-caine” anesthetics.

A

Transmembrane (“TM”) domains 5-6 act as a pore when activated by voltage sensing domain 4 on the Na+ channel. Though the Na+ channel may be activated, -caine anesthetics block the pore formed by TM5-TM6

9
Q

Tetrodotoxin acts as a (permanent/transient) blocker of Na+ channels.

A

permanent

10
Q

K+ channels are comprised of 6 transmembrane domains (S1-S6). Which act as a voltage sensor, and which form the K+ channel pore?

A

S1-S4: voltage sensor

S5-6

11
Q

Explain the K+ selectivity filter’s “Mechanism of Action.”

A

K+ is solvated in ICF. The large (10Angstrom) K+ channel pore will allow solvated K+ to enter. However, as the solvated K+ approaches the extracellular leaflet, the width decreases to 3 angstroms. The K+ is desolvated by the carbonyl groups there, and each subsequent positive, desolvated K+ is “repelled” out of the channel.

DRAW OUT!!!

12
Q

What is the AA sequence for the K+ selectivity filter

A

TVGYG

13
Q

Explain the Gibbs free energy basis for ion conductance through a K+ channel and how it affects selectivity.

A

To pass through a K+ channel, ions must be desolvated, then resolvated once through the channel.

For K+, the total change in E* for desolvation/solvation via the K+ channel is (-), or favorable.

For Na+, the total change in E* for desolvation/solvation via the K+ channel is (+), or unfavorable.

14
Q

Voltage gated channels change formation due to _____

A

changes in membrane potential.

15
Q

Inactivation of a voltage gated channel occurs through an “inactivation domain.” What end of the channel protein is this located (C-term/N-term)?

A

C-terminus

16
Q

Describe the steps of voltage gate inactivation:

A

1) An action potential (depolarization) opens the channel

2) Eventually, hyperpolarization moves the ball into the intracellular portion of the pore opening

17
Q

Describe the structure of the ACH-R

A

2xα; β; γ; δ

18
Q

Differing [Na+] and [K+] are generated by _____.

A

Na+/K+/ATPase pumps in the plasma membrane

19
Q

Outline the steps of an action potential

A

1) Transient changes in membrane potential reach a threshold
2) Conductance of Na+ rises by opening of v-gated Na+ channels secondary to the S4 “switch” domain
3) Depolarization occurs by Na+ flowing through S5-S6 pores
4) At +35mV, Na+ inactivation gate closes, and K+ channel opens
5) K+ efflux hyperpolarizes the cell
6) At -90mV (appx.) the K+ inactivation gate closes and hyperpolarization stops
7) Na/K/ATPase pumps return cell to RMP

20
Q

Explain the transmission of an action potential at the NMJ.

A

1) An action potential reaches the telodendria
2) Depolarization opens voltage gated-Ca2+ cells
3) Calcium enters the cell and causes fusion of vesicle PM/telodendria PM (SNAP protein)
4) Exocytosis of NT
5) Binds to receptor
6) Opening of ligand-gated channels on post-synpatic tissue causes Na+/K+ movement (Na+ influx > K+ efflux)
7) If depolarization is large enough, end plate potential produced (is this just in muscle?)
8) PMCA removes Ca2+ from telodendria (Ca2+ is cytotoxic)

21
Q

“Cell to cell” channels important to action potential/cell communcation.

A

Gap junctions

22
Q

Describe structure of gap junctions

A

One channel is comprised of 12 connexins. 6 connexins make 1 connexon. 2 connexons make one f(x) channel.*

*1 connexon on one cell, 1 connexon on the other

23
Q

Explain the selectivity of gap junctions

A

Gap junctions are

24
Q

Explain why connexons are important in tissue like the lens of the eye and bones.

A

These tissues lack abundant vasculature. Therefore, gap junctions provide a means of nourishment.

25
Q

What closes gap junctions?

A

High [Ca2+] and [H+]. These molecules are cytotoxic/inducers of apoptosis.

26
Q

How are connexons regulated

A

Hormone induced phosphorylation/membrane potential changes

27
Q

Describe how a gap junction is different from an ion channel.

A
Ion channel:            
Spams 1 PM
ICF to ECF connection
Synthesized by 1 cell
Rapid open/close
Gap:
Spans 2 PM
Cytosol to cytosol connection
Synthesized by 2 cells
Open for seconds/minutes
28
Q

Aquaporins are found in RBCs, kidneys, and corneas. Why?

A

These tissues require large amounts of water to be extruded past cell membranes.

29
Q

Describe the structure of aquaporins.

A

6 transmembrane spanning alpha domains

30
Q

Transport channels are responsible for ______ transport.

A

facilitated, passive

31
Q

What molecules are gap junctions permeable to?
A. Proteins, polysaccharides, and nucleic acids
B. Large, hydrophillic (> 1kDa) molecules
C. Small hydrophillic (

A

C. Small hydrophillic molecules