Chapter 3 - Resting Membrane Potential Flashcards
intracellular environment has a negative electrical charge compared to the extracellular environment
cell is at rest
water
- key ingredient in intracellular and extracellular environment
- uneven charge
- polar
- covalent bonds
atoms or molecules with a net electrical charge
ions
held together by ionic bonds (electrical attraction of oppositely charged ions)
NaCl
dissolve in water due to uneven electrical charge (salt)
water loving
polarity of water molecule and an uneven (polar) electrical charge
hydrophilic
does not dissolve in water due to even electrical charge
- non polar covalent molecules
- shared electrons are distributed evenly (no net charge)
hydrophobic
Polar phosphate head group
PO4 atom and 3 oxygen atoms attached at one end
- hydrophilic
Building the Prototypical Neuron
1) lipid bilayer
2) membrane spanning channel proteins inserted into the lipid bilayer
3) receptor proteins
small subunit binds the
mRNA
large subunit bidns the
tRNA
all amino acids
- central carbon atom (alpha carbon) covalently bonded to 4 molecular groups:
1) hydrogren atom
2) amino group
3) carboxyl group
4) residue group (varient)
join the amino group of one amino acid to the carboxyl group of another
peptide bond
chain of amino acids
polypeptide
primary structure
sequence
secondary structure
a-helix
spiral-like
tertiary structure
interactions with R-groups
Quaternary structure
over all structure
multiple peptide subunits
aggregate of subunits via weak molecular
bonds
polar r groups will ____ lipid environment
avoid (hydrophilic)
non polar r groups will ____ with lipids
associate (hydrophobic)
embedded (suspended) proteins
if proteins are arranged so that middle groups are non-polar and ends are polar.
channel proteins
4-6 subunits ion selectivity - size of pore - r group lining - k+, Na+, Ca 2+, Cl- gating: closed or open
Na+ ions are ____ than K+ ions
smaller
site channel that weakly binds to Na + ions
Na + selectivity filter
Berti Hille et al (1984)
- positive charge of ion is stabilized at a negative AA residue
- H2O molecule is attracted to a second amino acid residue on the other side of the channel
- K+ ion would be too large to bind effectively and would therefore be excluded.
The movement of ions: passive processes
1) diffusion
2) electrostatic processes
Diffusion
Dissolved ions distribute evenly
Ions flow down a concentration gradient
channels permeable to specific ions
concentration gradient across the membrane
opposite charges attract
like charges repel
electrical (electrostatic) processes
movements of ions: electricity
I: current
g: conductance
r: resistance
v: electrical potential
movement of electrical charge
measured in amps
current (I)
relative ability for the charge to migrate
measured in siemens (S)
conductance (g)
inability of the charge to migrate
measured in Ohms
Resistance (R)
difference in charge between anode and cathode
measured in volts (V)
electrical potential (V)
electrical current flow across a membrane
electricity
deals with the relationship between voltage and current in an ideal conductor. This relationship states that:
The potential difference (voltage) across an ideal conductor is proportional to the current through it.
Ohm’s law
The constant of proportionality is called the “resistance”, R.
Ohm’s Law is given by:
V = I R
where V is the potential difference between two points which include a resistance R. I is the current flowing through the resistance. For biological work, it is often preferable to use the conductance, g = 1/R; In this form Ohm’s Law is:
I = g V
Ohm’s law
The constant of proportionality is the “resistance”, R.
conductance, g = 1/R
I = g V
voltage potential across the neuronal membrane
membrane potential
at rest (RMP)
-65 - -70 mV
concentrations of ions at rest inside the cell Na+ K+ Cl- Ca2+ Protein
Na+ few K+ lots Cl- fewer Ca2+ fewer Protein many
concentrations of ions at rest outside the cell Na+ K+ Cl- Ca2+ Protein
Na+ lots K+ few Cl- more Ca2+ more Protein few
without channels
no movement of ions when separated by a phospholipid bilayer
Water chemically combined with a substance in such a way that it can be removed, as by heating, without substantially changing the chemical composition of the substance.
waters of hydration
K+channels inserted: > K+inside (large concentration gradient =diffusion)
A - are left behind: cell would have net negative charge
Equilibrium potential (K+)
there is a point when the inside of the cell is so negative it will start to draw the pos charged molecles back into the cell electrical fore (+/-) counterbalances the force of diffusion pushing K+ out (no net movement)
Equilibrium potential (K+) = -80mV
greater [Na+] outside
Na+ channels inserted:
- Na+ flows down conc gradient into the cell
- electrical forces also drive cell from pos environment to neg environment
- cell is more positive
reach a point when the charge is also positive it inhibits movement of Na+
Equilibrium potential for Na+
= +55 mV
calculates the exact value of an equilibrium potential in mV
- takes into consideration:
- charge of ion
- temperature
- ratio of the external and internal ion concentrations
Nernst Equation
E(ion)=2.303 RT/ZF logs ([ion]o/[ion]i)
E(ion) = equilibrium potential RT = gas constant Z = ion charge F = faraday's constant [ion]o = external ion concentration [ion]i=internal ion concentration
the distribution of ions across the membrane
K+: 80 mV
Na+: 62 mV
Ca2+ : 123 mV
Cl-: -65 mV
the membrane is more permeable to Na+ or K+?
K+
Takes into account permeability of membrane to different ions
P=Permeability [ion] concentration inside or outside Constants R and F (Nernst) T= temperature (Kelvin) Log function
Goldman equation
shape changing
allosteric
how many subunits are in a K+ channel
4 subunits
channel selectively permeable to K+ ions
pore loop
The importance of regulating the external potassium concentration
Increasing extracellular K+ will lead to a depolarization of the membrane.
what does the blood brain barrier do to the flow of K+
blood brain barrier limits the flow of K+
K+ pumps that take up K+
potassium spatial buffering (astrocytes)
differences between channels and pumps/transporters:
1.Channels are passive conduits, pumps transport ions against the electrochemical gradient (expending energy)
2.Ion transport is much faster in channels
Channels: 10^7– 10^8
ions/second
Transporters: 10,000 times slower
The sodium-potassium pump
transporter
Enzyme - breaks down ATP when Na+ present
1 molecule of ATP/hydrolyzed/cycle Na+/K+- ATPase
ATP-ligand
The calcium-pump (and more)
Calcium concentrated outside of the cells
Calcium pump: Actively transports Ca2+ out of cytosol
Calcium is a very important intracellular signal:
Mitochondria
ER
NT release
Conclusions: Neuron at Rest
Activity of the sodium-potassium pump
Movement of K+ ions across membrane Electrical potential difference across the membrane Similar to a battery Potassium channels Contribute to resting potential Roles of ion pumps
