Ion channels and Ca2+ signalling Flashcards
True or False
- Ion channels are coupled to an energy source for active transport.
FALSE
Are not coupled to an energy source for active transport.
Transport is always “passive”.
what is the difference between an active and passive ion channel?
- Active channels - have gates that can open or close
- Passive channels (leakage) are always open and ions pass through them continuously
what 3 things does an ion channel need to function?
-
A transmembrane pore
* Selectivity for the charge and size of the ion
2. A sensor “switch” for gating
- A membrane potential sensor (VOLTAGE gated ion channel)
- Neurotransmitter binding site (LIGAND gated ion channels)
3. Regulation mechanisms
- in-built “inactivation” switch
- modulation: G proteins, 2nd messengers, protein kinases
- localisation (e.g. post synaptic density)
what is the function of the pore vestibule in ion channels?
the pore vestibule facilitates the transport across the membrane by allowing ions to remain hydrated, because the ends of the selectivity filter at the outer entrance dehydrates ions
active channels (gated) alternate between open and closed conformations, what are the 4 different gating mechanisms.
how many transmembrane domains does a K+ voltage-gated ion channel have
and which one is considered the voltage sensor part
6 transmembrane domains
the 4th one is considered a voltage sensor
what does the S4 helix contain that is attracted to negative intracellular charge and causes the conformation of the channel to close?
what causes the channel to then open?
the S4 helix contains positively charged amino acids that are attracted to the negatively charged intracellular channel allowing the channel to form the closed conformation
the channel is opened when the membrane is depolarised, opening the pore and activating the channel
what is the name of the mechanism that blocks voltage-gated ion channels in the inactivated state?
how does it work?
the ball and chain mechanism
an intracellular region of the channel protein blocks the pore from being open too long
what the membrane is high polarized when the Na+ ion channels are in the ______ state
in this state, the ion channel is in a very low/high energy conformation
resting
low
what are the two main types of Ca2+ channel?
and where are they found?
- L-type Ca2+ channel, found in smooth and cardiac muscle
- N-type Ca2+ channel, found in neurons
what is the function of cation channels such as sodium ion channels?
cation channels (main sodium) are for depolarising and hence exciting the cell following an action potential.
what is the function of voltage K+ channels?
voltage returning the depolarized cell to a resting state after each nerve impulse
what is the function of voltage-gated calcium channels?
voltage-gated calcium channels are for evoking an action potential to depolarise the cell.
what are the two types of glutamate receptor?
AMPA
NMDA
what are the 3 key differences between AMPA and NMDA receptors?
- NMDA receptors require glycine as a cofactor to be activated, AMPA receptors don’t
- NDMA receptors have to be depolarised to be active, AMPA receptors are highly permeable to Na2+ as long as glutamate is bound
- NMDA receptors let calcium ions in as a second messenger
Calcium dynamics:
is this a list of ON or OFF calcium mechanisms?
ON Mechanisms
Calcium dynamics:
is this a list of ON or OFF calcium mechanisms?
OFF Mechanisms
