Lecture 2 (Membrane Potentials) Flashcards
Describe the membrane lipid bilayer
- Low electric conductivity
- Acts like an insulator
- Separates the EXTRACELLULAR FLUID and CELL CYTOPLASM and accumulation of opposite charges on both surfaces of membrane
Biological membranes are _________________
Capacitors
a device used to store electric charge
Describe the components of a Capacitor
- Made up of 2 close conductors separated by a DIELECTRIC MATERIAL
- Plates accumulate electric charge when connected to a power source
- One plate accumulates positive charge and the other accumulates negative charge
What is a Capacitor?
An electronic component that stores electric charge
What is the Capacitance?
The amount of electric charge that is stored in the capacitor at voltage of 1 Volt
Measured in units of FARAD (F)
What is the equation for Capacitance?
C = Q / V
C = Capacitance in farad (F)
Q = Electric charge in coulombs (C) stored in the capacitor
V = Voltage between the capacitor’s plates in volts (V)
_________ _________ membrane is an insulator (dielectric) which has a capacitance
Lipid bilayer
What is Coulomb’s law equation and what does it state?
F = k \frac{q_1q_2}{r^2}
F = electric force
k = Coulomb constant
q_1, q_2 = charges
r = distance of separation
- As charge increases so does the electric force
- As distance increases, the electric force decreases
What is the constance Ke equal to?
1/(4πε0) where ε0 is a constant known as the PERMITTIVITY OF A VACUUM
What is ε?
- Permittivity (characterizes the tendency of the atomic charge in an insulating material to distort in the presence of an electric field)
- A measure of how easily a medium is polarised by an electric field
- Dielectric constant of the medium
Is permittivity temperature dependent?
YES
What does the dielectric constant of water being very high reflect?
Water’s exceptional ability to conduct electricity
Explain why water has a high permittivity
The polar molecules of water have -ve ends facing +ve charge and +ve ends facing -ve charge -> Orientation creates small electric fields that oppose the electric fields of +ve and -ve charge in the medium -> This reduces the FORCE & POTENTIAL ENERGY between +ve and -ve charge
_________ is directly proportional to voltage and inversely proportional to resistance
Current
What is the equation to calculate current?
I = V / R
I = current (amperes)
V = electromotive force (volts)
R = resistance (ohms)
A flow rate of how many electrons per second is an electrical current of 1 Ampere (Amp)?
6.24 X 10^18
Describe the electric model of the membrane
- Contains CAPACITANCE (lipid bilayer) and OHMIC (ions’ protein channels) RESISTANCE
- Capacitance and Ohmic resistance defines the SELECTIVE PERMEABILITY to ions and determines ions’ non-equal redistribution on both sides of membrane
- Formation of chemical and electrical gradients and potential difference
What is Membrane potential (V) measured by?
Difference in potential between the inside minus the outside (V INSIDE - V OUTSIDE)
What does Resting potential determine?
Energy storage (Em) essential for regulation of cell homeostasis
What happens if the membrane is permeable just for potassium ions?
K+ will be transported from high concentration area to low concentration area -> Charge separation occurs and a voltage develops across the membrane
What does the Diffusion force depend on?
Ions’ concentration in both compartments of the container
What does the Electrostatic force depend on?
Ions’ valency and the difference of potentials between membrane surfaces
What is the Nernst equation?
The Nernst equation defines the electrochemical equilibrium between a concentration gradient and an electrical potential, for one particular ion.
The electrical potential that exactly balances a concentration gradient is called the reversal potential. The Nernst equation reveals how the reversal potential of an ion depends on the inside and outside concentrations of this ion
What does the Goldman-Hodgkin-Katz equation calculate?
The resting potential
The resting potential of a cell is a compromise between the reversal potentials of all ions to which the membrane is permeable
What is Donnan’s equilibrium?
It refers to the uneven distribution of charged particles on one side of a semi-permeable membrane.
However, if there is an IMPERMEABLE SOLUTE in one of the solutions, the concentration doesn’t equalise. The concentration of the solution with impermeable solutes remains high even at equilibrium.
The flow of molecules and ions between a cell and its environment is regulated by which effect?
Donnan effect
`What is the mechanism that prevents cells from swelling and rupturing?
The Na+ K+ pump
It prevents cells from rupturing by continuously pushing out excess ions
What is the oncotic pressure of blood responsible for?
Non-equal distribution of ions in blood and interstitial space
