Week 1

Question 1

What is the plasma membrane made of?

Answer 1

• A bilayer of phospholipids.
• Heads point out to H20; are negatively charged and hydrophilic
• Tails are hydrophobic and uncharged

Question 2

How thick is the plasma membrane?

Answer 2

~5nm

Question 3

What is permeable across the plasma membrane?

Answer 3

Small and uncharged lipophilic substances

Question 4

What is the protein structure of a typical ion channel?

Answer 4

• 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

Question 5

How can ions rapidly and selectively permeate ion channels?

Answer 5

• 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

Question 6

What is the Nernst equation?

Answer 6

Defines the membrane potential at which the flow of an ion is balance from inside to outside (reversal potential)

Question 7

What happens if you inject a square current pulse into the cell?

Answer 7

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:

Question 8

What is meant by the membrane time constant?

Answer 8

= R_m * C_m
Indicates how fast the capacitor charges, how quickly V_m reaches steady state.

Question 9

How does measure of current depend on location in a neuron?

Answer 9

Dendrites have worse conductivity and capacity than axons, cable properties. They will have smaller and slower V_m change.

Question 10

What is the Goldman-Hodgkin-Katz Equation?

Answer 10

Question 11

What is meant by the membrane length constant?

Answer 11

sqrt(R_membrane / R_axon). Larger means more propagation through axons.

Question 12

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)

Answer 12

• 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.

Question 13

INTRA and EXTRA concentrations of Na, K, Cl, Ca

Answer 13

INTRA:
10mM
150mM
5mM
100nM

EXTRA:
150mM
5mM
120mM
1mM

Question 14

How does the course define positive current? And membrane potential?

Answer 14

Positive charge flowing outward. Inside minus outside.