4. Membranes and membrane proteins Flashcards
Why water (6)?
- Can interact with charged particles - electrostatic interactions can occur.
- Hydrophobic and hydrophilic lipids allow self assembly of proteins in water.
- Thermal fluctuctuations are provided by Brownian motion - water molecules are a good size
- Adjusts to differnent pH by disociating
- DNA is charged in water due to pK of water
- Salts dissolve in water - useful because salts acan influence rate of reactions since many reactions rely on identifcation of specific surfaces.
What is the charge density of DNA
-2e per bp
Why are electric forces smaller in water?
Water dipoles orient themselves with the field which acts to reduce it.
Bjerrum length =
the separation of two particles at which the electrostatic energy is comparable to the thermal
about 0.7 nm in water
Poisson Boltzmann equation
d^2V/dx^2 = 2z^2 e^2 c_infinity/DE_0
Debye screening lenght
Why are positively charged ions often used for signalling?
Because macromolecules are often negative ie DNA, actin
Draw a circuit diagram of the Hodgkin Huxley model
Define the membrane voltage
= V_in -V_out = V_2 -V_1
Derive the Nernst equation
Donnnan equilibrium =
in equilibrium the Nernst potential is the same for all ion species and is equal to the membrane potential
Name 3 assumptions of the H-H model
- Different ion channels are independent
- Activation and inactivation of different channels is independent.
- Model cell is iospotential across the membrane
Derive the Goldman equation
How do cells operate far from the Donnan equilibrium?
By pumping ions across the membrane. This requires energy
How can cells be divided into cell types?
By their resting potential
How much energy is required to pump an ion across a membrane?
eV_nernst + eV_membrane