Chapter 3 - Resting Membrane Potential Flashcards
1
Q
intracellular environment has a negative electrical charge compared to the extracellular environment
A
cell is at rest
2
Q
water
A
- key ingredient in intracellular and extracellular environment
- uneven charge
- polar
- covalent bonds
3
Q
atoms or molecules with a net electrical charge
A
ions
4
Q
held together by ionic bonds (electrical attraction of oppositely charged ions)
A
NaCl
5
Q
dissolve in water due to uneven electrical charge (salt)
water loving
polarity of water molecule and an uneven (polar) electrical charge
A
hydrophilic
6
Q
does not dissolve in water due to even electrical charge
- non polar covalent molecules
- shared electrons are distributed evenly (no net charge)
A
hydrophobic
7
Q
Polar phosphate head group
A
PO4 atom and 3 oxygen atoms attached at one end
- hydrophilic
8
Q
Building the Prototypical Neuron
A
1) lipid bilayer
2) membrane spanning channel proteins inserted into the lipid bilayer
3) receptor proteins
9
Q
small subunit binds the
A
mRNA
10
Q
large subunit bidns the
A
tRNA
11
Q
all amino acids
A
- central carbon atom (alpha carbon) covalently bonded to 4 molecular groups:
1) hydrogren atom
2) amino group
3) carboxyl group
4) residue group (varient)
12
Q
join the amino group of one amino acid to the carboxyl group of another
A
peptide bond
13
Q
chain of amino acids
A
polypeptide
14
Q
primary structure
A
sequence
15
Q
secondary structure
A
a-helix
spiral-like
16
Q
tertiary structure
A
interactions with R-groups
17
Q
Quaternary structure
A
over all structure
multiple peptide subunits
aggregate of subunits via weak molecular
bonds
18
Q
polar r groups will ____ lipid environment
A
avoid (hydrophilic)
19
Q
non polar r groups will ____ with lipids
A
associate (hydrophobic)
20
Q
embedded (suspended) proteins
A
if proteins are arranged so that middle groups are non-polar and ends are polar.
21
Q
channel proteins
A
4-6 subunits ion selectivity - size of pore - r group lining - k+, Na+, Ca 2+, Cl- gating: closed or open
22
Q
Na+ ions are ____ than K+ ions
A
smaller
23
Q
site channel that weakly binds to Na + ions
A
Na + selectivity filter
24
Q
Berti Hille et al (1984)
A
- 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.
25
The movement of ions: passive processes
1) diffusion
| 2) electrostatic processes
26
Diffusion
Dissolved ions distribute evenly
Ions flow down a concentration gradient
channels permeable to specific ions
concentration gradient across the membrane
27
opposite charges attract
| like charges repel
electrical (electrostatic) processes
28
movements of ions: electricity
I: current
g: conductance
r: resistance
v: electrical potential
29
movement of electrical charge
| measured in amps
current (I)
30
relative ability for the charge to migrate
| measured in siemens (S)
conductance (g)
31
inability of the charge to migrate
| measured in Ohms
Resistance (R)
32
difference in charge between anode and cathode
| measured in volts (V)
electrical potential (V)
33
electrical current flow across a membrane
electricity
34
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
35
Ohm's law
The constant of proportionality is the "resistance", R.
conductance, g = 1/R
I = g V
36
voltage potential across the neuronal membrane
membrane potential
37
at rest (RMP)
-65 - -70 mV
38
```
concentrations of ions at rest inside the cell
Na+
K+
Cl-
Ca2+
Protein
```
```
Na+ few
K+ lots
Cl- fewer
Ca2+ fewer
Protein many
```
39
```
concentrations of ions at rest outside the cell
Na+
K+
Cl-
Ca2+
Protein
```
```
Na+ lots
K+ few
Cl- more
Ca2+ more
Protein few
```
40
without channels
no movement of ions when separated by a phospholipid bilayer
41
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
42
K+channels inserted: > K+inside (large concentration gradient =diffusion)
A - are left behind: cell would have net negative charge
Equilibrium potential (K+)
43
```
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
```
44
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
45
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
```
46
the distribution of ions across the membrane
K+: 80 mV
Na+: 62 mV
Ca2+ : 123 mV
Cl-: -65 mV
47
the membrane is more permeable to Na+ or K+?
K+
48
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
49
shape changing
allosteric
50
how many subunits are in a K+ channel
4 subunits
51
channel selectively permeable to K+ ions
pore loop
52
The importance of regulating the external potassium concentration
Increasing extracellular K+ will lead to a depolarization of the membrane.
53
what does the blood brain barrier do to the flow of K+
blood brain barrier limits the flow of K+
54
K+ pumps that take up K+
potassium spatial buffering (astrocytes)
55
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
56
The sodium-potassium pump
| transporter
Enzyme - breaks down ATP when Na+ present
1 molecule of ATP/hydrolyzed/cycle Na+/K+- ATPase
ATP-ligand
57
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
58
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
```
