Ion Channel Structure
We focused on these two types of gating for ion channels examined in class.
What is voltage gated and ligand gated?
This biological structure acts as a capacitor in the cellular circuit.
What is a cell membrane?
We can measure the current flowing into/out of a cell (with a constant voltage) because of the movement of what type of molecule?
What are ions?
The eggs of this animal are often used to express channel types scientists are interested in studying.
What is Xenopus laevis? (or, what is the African clawed frog?)
Ionotropic receptors are so named because they let this type of particle pass through their pore?
What is an ion?
Members of this receptor family have 5 subunits with 4 transmembrane domains each.
What is the nACh receptor family?
These two properties determine the quality of a capacitor.
What is surface area and quality of the insulator?
This characteristic of the cell membrane makes it an excellent capacitor.
What is polarity, or hydrophilic heads and hydrophobic tails?
These two animals were vital for isolating the structures of voltage gated sodium channels and nicotinic acetylcholine receptors because of their extremely high endogenous concentrations.
What are the electric eel (NaV) and electric ray torpedo (nAchR)?
This characteristic allows some ions to enter the cell instead of others.
What is selective permeability?
This molecule lining the pore of voltage gated potassium channels allows for high selectivity of potassium over sodium.
What is oxygen?
Introducing a capacitor to a circuit introduces what additional consideration to calculations of voltage and current?
What is time dependency?
Increasing this characteristic of a cell will increase its overall input capacitance.
What is surface area?
This toxin blocks voltage gated sodium channels (NaV) with very high specificity, allowing for experimental isolation of different types of receptors.
What is tetrodotoxin (TTX)?
Only this type of subunit is required for voltage gated sodium channel functionality.
What are alpha subunits?
On a hydrophobicity plot, a string of hydrophobic amino acids indicates this about the receptor structure.
What is the presence of a transmembrane domain?
What is 100%?
Having more channels in a cell membrane decreases this electrical quantity.
What is resistance?
These two techniques are our best tools for visualizing membrane proteins.
What are cryogenic electron microscopy and X-ray crystallography?
This type of receptor mediates synaptic excitation at the neuromuscular junction.
What are nAChRs?
This region on a channel is responsible for determining selectivity.
What is the P loop?
What is the approximate input capacitance of a smooth, spherical cell 70 um (microns) in diameter? Recall area of a sphere = 4(pi)r^2 and cellular capacitance/unit area = 1uF/cm^2
154 pF
Ion channels compose these two parts of a complete circuit.
What are resistance/conductance and the battery?
This technique in molecular biology allows experimenters to determine the importance of specific amino acid residues.
What is sequence mutation?
This is partly the reason potassium channels have greater diversity in type than sodium channels.
Why do potassium channels have 4 subunits?