channels and transporters lecture 3

Question 1

where are non gated and gated ion channels found

Answer 1

bacteria, archaea, eukaryotes

Question 2

describe the structure of K+ channels

Answer 2

6 TM helices. 1-4 form the voltage sensing domain. 5 and 6 form the channel

Question 3

what is KscA

Answer 3

the first K+ channel to be discovered and only has 2 TM helices.It has a P-helix at the top of the cone structure and part of the P segment which contians the selectivity filter.

Question 4

what does the bottom of the KscA channel contain

Answer 4

it is hydrated in the bottom of the vestibule.

Question 5

describe the structure at the top of the channel of KscA

Answer 5

surrounded by stretch of amino acids held in place by P segment. conserved in potassium channels. in potassium channels carbonyl groups line the channel.

Question 6

what is observed in the crystal structure of KscA

Answer 6

4 dehydrated potassium ions at the top.

Question 7

what provides selectivity to KscA

Answer 7

the 8 ligands and electrostatic repulsion of neighbouring potassium ions weakens bonding.

Question 8

what is the structure of sodium and calcium channels.

Answer 8

have a single chain pseudo-tetrameric structure

Question 9

how is selectivity achieved in sodium and calcium channels

Answer 9

different selectivity filters.wha

Question 10

what was the first sodium channel to be discovered

Answer 10

NavAb which is voltage gated form proteobacterium.

Question 11

what does NavAb sodium channel contain

Answer 11

P hleix, P2 half helix, short loop between the two which is responsible for selectivity.

Question 12

how are CaV and NaV told apart

Answer 12

the ion selectivity is dictated by the sidechains.

Question 13

how does NaV transport Na+

Answer 13

in a partly hydrated form which can during transport.

Question 14

what does the selectivity filter side chain of Na contain

Answer 14

Glu

Question 15

is the filter in NaV less conserved than in Kv

Answer 15

yes

Question 16

describe voltage gating in Nav channels

Answer 16

s1-4 is voltage sensing. 4 has positive residues that respond to the membrane potentials. the movement from here goes to 5-6 via S4-5 hleix. forces open S6 which opens channels. this happens at the bottom at activating gate. the hinge in S6 is a glycine residue.

Question 17

how do NaV and Kv channls inactivate

Answer 17

they have a second gate that inactivates spontaneously after few ms.

Question 18

where is the channel inactivating segment located

Answer 18

Kv shaker channels at N-terminus

Question 19

how to you get shaker like properties

Answer 19

this happens because of domain swapping of the shaker domain in related K+ channels

Question 20

name the 7 transient receptor potential channels

Answer 20

TRPC, TRPV, TRPM, TRPA, TRPN, TRPML, TRPP

Question 21

can TRP channels sense many stimuli

Answer 21

yes

Question 22

does the S1-4 domain move in trp channels

Answer 22

no but opening and closing is still gated by S6

Question 23

what are trp channels selective for and what do they transport

Answer 23

cation selective. transport monovalent and divalent cations

Question 24

what is the primary function of TRPV1

Answer 24

nociceptor to stimulate immune and pain response.
can be sensitised by other inflammatory components leading to thermal hyperalgesia.

Question 25

what does TRPV1 respond to

Answer 25

noxious temperatures, acidic PH, arachidonic acids metabolites and endocannabinoids

Question 26

what is the primary function of TRPM8

Answer 26

cold detector

Question 27

what does TRPM8 respond to

Answer 27

gentle cooling, menthol, icilin, eucalyptol, linalool, geraniol, hydroxycitronellal,

Question 28

what do low doses of methanol do

Answer 28

lower threshold for cold detection

Question 29

what are uniport, symport and antiport

Answer 29

they are substrate specific, known as carriers, permeases, transporters and channels.

Question 30

how can symporters become uniporters

Answer 30

by small mutations

Question 31

what is the function of uniporter

Answer 31

facilitative transport

Question 32

function of symporter and antiporter

Answer 32

co transport

Question 33

what energy do symporters and antiporters use

Answer 33

energy from sodium and proton gradients

Question 34

what can the substrate of symporter/anti porter be

Answer 34

organic metabolite, nutrient, toxin,cation or anion.

Question 35

give an example of a symporter

Answer 35

SGLT1

Question 36

what is the bacterial homologue structure of Leucine symporters

Answer 36

occluded state. sodium doesn’t bind without leucine. sodium is bound in dehydrated form. one sodium coordinates leucine substrate.

Question 37

transcellular transport in intestine epithelium involves what

Answer 37

SGL1-symporter
GLUT2-uniporter
primary active ATPase
potassium channel
glucose in cytoplasm is high
GLUT transports glucose into blood.