neuro establishing membrane Flashcards
b. A + B–> E –>AB
cell needs to have the right substrates and molecules in order to perform this reaction
all about protein synthesis and the role of the membrane
cellular physiology begins with access to the internal environment when a cell is
Selective permeable
at the membrane
describe membrane structure
i. Phospholipid bilayer oriented so heads are exterior and interior surfaces of the membrane; tail groups are directed inward towards the center of the membrane
hydrophobic inner
Fluid Mosaic Model)
describe membrane proteins that are relatively free to float around in the membrane and they can concentrate in certain areas of the membrane if needed
types of movements allows by phospholipid bilayer
simple and facilitated (you need a transport molecule to bind)
diffusion can be facilitated
this is how glucose moves
b. Factors that affect diffusion and diffusion rate:
i. Permeability (P) of the membrane
ii. Area: D = PxA
iii. Concentration Difference D(Co-Ci)
diffusion as it relates to permeability and area
a. Diffusion = permeability x area
size of a gradient also impacts net diffusion
V. When does movement of substances across selectively membrane stop?
Diffusion proceeds to equilibrium, NOT equal concentrations
If only one substance and no concentration gradient, then your net diffusion will be 0 but usually other forces and molecules in play
An _________ can make charged particles move in the absence of a concentration gradient
An electric potential can make charged particles move in the absence of a concentration gradient
VI. Nernst Potential
Find the equilibrium point for an ion in solution when there is a semipermeable membrane that is permeable to that ion
equilibrium potential
should be able to apply a positive charge that would counteract diffusion or concentration gradient
allows us to figure out the electrical current at which point the system would be in equilibrium
Nerst equation only works with what types of ions
univalent
so not Ca (2+)
osmotic pressure is created with
non diffusible elements on either side of the membrane
osmole is
the molar content of non diffusible elements
what is needed to phosphorylate enzymes
i. Need ATP to phosphorylate enzymes
In nerve and muscle physiology, this is important for establishing the concentration gradient that we need to use to create that electric voltage we need across the membrane
Na/K pump
functions of Na/K pump
Helps maintain osmotic balance
Electrogenic (separates charge unevenly and creates potential for electrical current)
step 1 of Na/k pump
- takes in 3 Na molecules, which are bound to the protein.
step 2 of Na/k pump
ATP phosphorylates alpha subunit, stimulating conformational change
step 3 of Na/k pump after ATP phosphorylates alpha subunit, stimulating conformational change
Pump open to outside, ready to start second half of cycle
step 4 of Na/k pump after
Pump open to outside, ready to start second half of cycle
2 K accepted from outside
step 5 of Na/k pump after
2 K accepted from outside
dephosphorylation stimulates conformational change
step6 of Na/k pump after . dephosphorylation stimulates conformational change
- 2 K expelled to inside; pump returns to initial state
Na/k pump helps establish what charge
So moving 3 Na+ out, and 2 K+ in =net positive charge outside and net negative charge inside
this is a membrane phenomenon
remember sodium concentrations 134-145
whereas K 3.5-5
Active Transport Mechanisms: Secondary
spend ATP to set up gradient that allows us to move molecules in the same or opposite directions
imbalance of charge is a form of
“potential” energy
relative difference of electrical charge between the two sides of the membrane
diagram of pulling back the bow from the arrow
forces at play with a cell and how they relate to NERST
membrane is relatively permeable to potassium
Na/k creates high intracellular K
flux of K ions would want to move out but
electrostatic pressure: outside is more positive and this is a repelling force that keeps
as the ion is fluxing the concentration gradient is reducing diffusion pressure
NERST looks at the balances of these and looks at where you can apply an electrical current to stop the flow of ions even if the concentration is not equal
EMF =
electro
motor force
voltage that you have to apply to prevent the movement of ions
C1/C2
concentration inside and outside of the cell
Factors effecting diffusion potential
Polarity of each ion involved is important
Permeability of membrane for each ion
Concentration difference of each ion across membrane
Modified Nernst for multiple ions
: Goldman-Hodgkin-Katz equation
Calculates the membrane potential at rest given the different concentration gradients
GHK equation accounts for
Considers concentration differences of the ions most responsible for the membrane potential
Considers permeability because ions can only contribute to membrane potential if the membrane allows it/if they can diffuse
chloride and it’s negative charge is accounted for
GHK tells us
can us it to calculate the membrane potential at rest given the different concentration gradients
ions can only contribute to membrane potential if the membrane allows it/if they can _______
ions can only contribute to membrane potential if the membrane allows it/if they can diffuse
b. Voltage across membrane referred to as __________
b. Voltage across membrane referred to as “membrane potential”
c. In nerve cells, typically the membrane potential is
c. In nerve cells, typically -60- -90mV
Inside of the cell is more negative than the outside
remember the picture of the capacitor this is how the membrane acts
Factors influencing membrane potential
a. Activity of the Na/K pump
b. Membrane leak/Permeability
c. Effect of leak on membrane potential can be inferred from Nernst potential for each ion involved
d. Hyperpolarization by ATPase
If membrane only leaky to 1 of the ions, then that ion is going to….
If membrane only leaky to 1 of the ions, then that ion is going to move the membrane potential towards its own reversal potential
is i make the membrane permeable it will move the concentration toward equilibrium and it’s own reversal potential
can use the NERST to calculate where the potential would go in this case
membrane gets re-polarized by the
i. Gets repolarized by the ATPase
a. Vk
nerst potential/reversal potential for K is pretty negative
Vna
membrane potential is very positive; if open channels for Na, then it’s going to rush in to the cell
what this tells you is that Na is oging to rush into the cell
Vm
membrane potential is close to K’s reversal potential b/c of the leakiness to K, tending to keep the membrane near its own reversal potential
describe AP
When some threshold is reached, massive opening of Na channels and the membrane potential is driven towards the reversal potential for Na which is positive so you have the upstroke
when the membrane potential is drive back down this is an example of what physiological process
then slower K channels open and the membrane potential is driven back downward towards resting potential (downstroke)