channels and transporters lecture 3 Flashcards
where are non gated and gated ion channels found
bacteria, archaea, eukaryotes
describe the structure of K+ channels
6 TM helices. 1-4 form the voltage sensing domain. 5 and 6 form the channel
what is KscA
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.
what does the bottom of the KscA channel contain
it is hydrated in the bottom of the vestibule.
describe the structure at the top of the channel of KscA
surrounded by stretch of amino acids held in place by P segment. conserved in potassium channels. in potassium channels carbonyl groups line the channel.
what is observed in the crystal structure of KscA
4 dehydrated potassium ions at the top.
what provides selectivity to KscA
the 8 ligands and electrostatic repulsion of neighbouring potassium ions weakens bonding.
what is the structure of sodium and calcium channels.
have a single chain pseudo-tetrameric structure
how is selectivity achieved in sodium and calcium channels
different selectivity filters.wha
what was the first sodium channel to be discovered
NavAb which is voltage gated form proteobacterium.
what does NavAb sodium channel contain
P hleix, P2 half helix, short loop between the two which is responsible for selectivity.
how are CaV and NaV told apart
the ion selectivity is dictated by the sidechains.
how does NaV transport Na+
in a partly hydrated form which can during transport.
what does the selectivity filter side chain of Na contain
Glu
is the filter in NaV less conserved than in Kv
yes
describe voltage gating in Nav channels
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.
how do NaV and Kv channls inactivate
they have a second gate that inactivates spontaneously after few ms.
where is the channel inactivating segment located
Kv shaker channels at N-terminus
how to you get shaker like properties
this happens because of domain swapping of the shaker domain in related K+ channels
name the 7 transient receptor potential channels
TRPC, TRPV, TRPM, TRPA, TRPN, TRPML, TRPP
can TRP channels sense many stimuli
yes
does the S1-4 domain move in trp channels
no but opening and closing is still gated by S6
what are trp channels selective for and what do they transport
cation selective. transport monovalent and divalent cations
what is the primary function of TRPV1
nociceptor to stimulate immune and pain response.
can be sensitised by other inflammatory components leading to thermal hyperalgesia.
what does TRPV1 respond to
noxious temperatures, acidic PH, arachidonic acids metabolites and endocannabinoids
what is the primary function of TRPM8
cold detector
what does TRPM8 respond to
gentle cooling, menthol, icilin, eucalyptol, linalool, geraniol, hydroxycitronellal,
what do low doses of methanol do
lower threshold for cold detection
what are uniport, symport and antiport
they are substrate specific, known as carriers, permeases, transporters and channels.
how can symporters become uniporters
by small mutations
what is the function of uniporter
facilitative transport
function of symporter and antiporter
co transport
what energy do symporters and antiporters use
energy from sodium and proton gradients
what can the substrate of symporter/anti porter be
organic metabolite, nutrient, toxin,cation or anion.
give an example of a symporter
SGLT1
what is the bacterial homologue structure of Leucine symporters
occluded state. sodium doesn’t bind without leucine. sodium is bound in dehydrated form. one sodium coordinates leucine substrate.
transcellular transport in intestine epithelium involves what
SGL1-symporter
GLUT2-uniporter
primary active ATPase
potassium channel
glucose in cytoplasm is high
GLUT transports glucose into blood.
