What is the plasma membrane made of?
- A bilayer of phospholipids.
- Heads point out to H20; are negatively charged and hydrophilic
- Tails are hydrophobic and uncharged
How thick is the plasma membrane?
~5nm
What is permeable across the plasma membrane?
Small and uncharged lipophilic substances
What is the protein structure of a typical ion channel?
- Protein with a transmembrane domain
- Typically alpha helices with lipophilic property on outside of helix to interact with the lipid tails of the phospholipids.
- It is an alpha subunit, made of four tetramers, the ion channel being the aqueous pore between all four tetramers.
- Each tetramer is formed by subunits S1 through to S6.
- Charged amino acids in the pore that can interact with ions and water
How can ions rapidly and selectively permeate ion channels?
- Certain ion channels are permeable only to specific ions due to the charged amino acids in the aqueous pore. Negatively charged amino acids will repel anions etc
- Selectivity filter: allows only specific species of ions due to high affinity binding sit ein the pore
What is the Nernst equation?
Defines the membrane potential at which the flow of an ion is balance from inside to outside (reversal potential)
What happens if you inject a square current pulse into the cell?
Cell has some capacitance, and so charges. We have that membrane potential is:
V_m = I_m * R_m * [1 - e(-t / tau)]
Note the time scale:
What is meant by the membrane time constant?
= R_m * C_m
Indicates how fast the capacitor charges, how quickly V_m reaches steady state.
How does measure of current depend on location in a neuron?
Dendrites have worse conductivity and capacity than axons, cable properties. They will have smaller and slower V_m change.
What is the Goldman-Hodgkin-Katz Equation?
What is meant by the membrane length constant?
sqrt(R_membrane / R_axon). Larger means more propagation through axons.
What are the following for:
- Elementary charge (C)
- Avogadro’s constant (mol-1)
- Gas constant (J K-1 mol-1)
- Faraday constant (C mol-1)
- Ions for a given charge
- Defines the number of particles (atoms, molecules, etc.) in one mole of a substance
- PV=nRT; links Pressure, Volume, Temperature, no.Moles of gas
- Represents the total electric charge carried by one mole of electrons.
INTRA and EXTRA concentrations of Na, K, Cl, Ca
INTRA:
10mM
150mM
5mM
100nM
EXTRA:
150mM
5mM
120mM
1mM
How does the course define positive current? And membrane potential?
Positive charge flowing outward. Inside minus outside.
