physiological systems

Calculate the number of lipid molecules we added to each cell to make the tethered membrane.  (5 marks)

Molarity of lipid = 3mM

Volume added = 8mL

2.     Calculate the number of molecules of lipid in the tethered monolayer film on gold. (5 marks)

Area per tethered molecule = 1nm²

Area of gold electrode= 2mm²  

3.     What is the fraction of added phospholipid that is incorporated into the membrane? (3 marks)

4.     Calculate the number of molecules of gramicidin in 8ml of a 50nM solution. (5 marks)

5.     Assume the same fraction of gramicidin remains as part of the  membrane as the fraction of lipids (they are very similar molecular weights), then how many molecules of gramicidin are there in the membrane (3 marks)

6.     Calculate the approximate conductance generated per gramicidin (in pS) in the membrane. (4 marks)

Total Siemens generated = 5µS

 7. One can calculate membrane thickness from the relationship below between area plate separation and permittivity of a capacitor.

The following results were obtained from the biosensor experiment.

For a capacitor of area, A (m²) and thickness, d (m) the capacitance, Cm (F) is given by:

Cm = e₀ x e_r x A /d

wheree₀ is the permittivity of free space = 8.854 x 10^-12 F/m and

e_r is the relative permittivity of membrane lipid ~ 2.3 and area A = 3mm²

(a) Calculate the membrane thickness at the three different gramicidin concentrations. (9 marks)

    (b) What changes occur to the membrane thickness when more gA is added? Why might these changes be occurring? (4 marks)