Lecture 1: Membrane and electric 2023 Flashcards
What component of a circuit does the membrane resemble
a capacitor
2 plates –> membrane bilayer
build up/storage of charge
distance and area are proportional to the level of capacitance in plate capacitors
plasma mb capacitance is affected by SA and distance(mb thickness) but doesn’t change much
separated by 5nm generated large electric field
bilayer allows for segregation of environments hydrophobic inside, storage of charge
the resistors/conductors in cell
ion channels
same thing but inverse relationship
conductance of channels is gK
The source of power in the cell circuit model
electron motive force, electrochemical gradients
Potential Energy
voltage
measuring single channel current
down, depolarization current in the direction away from the electrode
Factors affecting membrane permeability
size, polarity of the molecules
polarity»_space; size
hydrophobic environments are highly impermeable ti charged ions regardless of size
non polar hydrophobic molecules
slips through easily,
ex. O2, CO2, N2, steroid hormones
small uncharged molecules
slightly permeable
ex. h2o , urea, glycerol
large uncharge polar molecules
barely making it
ex. sucrose, glucose
ions (charged molecules)
aint no way, without the presence of a protein channel
ex. H+, Na+ K+, Cl-
active forms of transport
require energy, going ion the opposite direction of gradient, require a protein complex usually transporter of some sort
passive transport
no E requirement, can require protein complex but not always
- simple diffusion
-channel mediated
-transporter mediated
“openness” of channel
resistance in ohms
voltage
potential difference can also be written as E in volts
conductance
inverse of resistance, in Siemens
Ohm’s Law
V= IR
capacitance
how much charge has to be transferred between 2 conductors to create a given potential (voltage) difference –> determines how much charge has to be generated
- determines how many ions must move to produce an electrical signal
inversely proportional to potential, and membrane thickness
measured in farads
proportional to surface area
C=Q/V
The cell membrane is a _______ circuit
parallel
ion channels are resistors added in parallel
why are ions channels considered parallel resistors
an ion won’t go through multiple channels but rather will go through any of the 3 –> equal opportunity
Ion channels along the axon
resistors in series
