Cell Membrane Flashcards
1
Q
What is the cell membrane?
A
- a phospholipid bilayer
- allows easy passage for small, non-polar, uncharged molecules
exocytosis 1
- secretory vessels fuse at fusion pores
- connect and disconnect multiple times
- part of the contents are empties
- low rate of signaling
exocytosis 2
- complete fusion of the vesicle with the membrane
- all contents releases at once
- counterbalanced by endocytosis
2
Q
Simple diffusion
A
- passage through a membrane either directly or through pores
- moves down [ ] gradient
- passive
- rate dependent on gradient
3
Q
Facilitated diffusion
A
- molecules diffuse by carrier proteins
- movement down the [ ] gradient
- passive
4
Q
Active transport
A
- movement against [ ] gradient
- substrate binds to protein carrier that changes conformation to move across membrane
- requires ATP hydrolysis
5
Q
Secondary Active transport
A
- against [ ] gradient without ATP catabolism
- kinetic energy of one substance down the gradient powers it
- also powered by the chemical energy by ions diffusing down the gradient
6
Q
Channels
A
- pores in the membrane
- physical properties create a selectivity filter
7
Q
Gated channels
A
- channels closed off by a gate, only opened in certain conditions
factors determining channel shape:
- ligand gated channels
- voltage gated channels
8
Q
Voltage gated channels
A
- sensitive to potential differences across the membrane
- positively charged s4 segments open like a wing at certain membrane potentials
- natural position of the wing is up towards the outer surface of the cell membrane
- wings pull downward to the inner surface when polarized
9
Q
Exocystosis
A
- moving cells out of the cell
-
10
Q
Na+/K+ pump
A
- 1 ATP : 3 Na+ out : 2 K+ in
11
Q
Resting membrane potential
A
- close to -70mV
- membrane most permeable to K+
- efflux of K+ occurs until K+ is repelled by electromagnetic force
- reaches equilibrium
12
Q
Equilibrium Potential
A
- electrical work to repel outward cation diffusion = chemical work of diffusion down [ ] gradient
- nernst equation»_space;> ideal situation
13
Q
K+ equilibrium potential
A
- potential is -90mV
- only when no other species are involved
14
Q
Na+ equilibrium potential
A
- membrane most permeable to Na+ causes and influx of Na+
- at equilibrium, there is a net cation accumulation inside the membrane
- ENa+ = +60 mV
15
Q
Na+ channels
A
- channels only open when depolarized to -55 mV
- once they open, the membrane becomes more positive causing a rapid influx of Na+
- inactivation at +30 mV by the ball and chain swinging shut (0.5 ms after)
