Cell Membrane

Question 1

What is the cell membrane?

Answer 1

• 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

Question 2

Simple diffusion

Answer 2

• passage through a membrane either directly or through pores
• moves down [ ] gradient
• passive
• rate dependent on gradient

Question 3

Facilitated diffusion

Answer 3

• molecules diffuse by carrier proteins
• movement down the [ ] gradient
• passive

Question 4

Active transport

Answer 4

• movement against [ ] gradient
• substrate binds to protein carrier that changes conformation to move across membrane
• requires ATP hydrolysis

Question 5

Secondary Active transport

Answer 5

• 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

Question 6

Channels

Answer 6

• pores in the membrane

- physical properties create a selectivity filter

Question 7

Gated channels

Answer 7

• channels closed off by a gate, only opened in certain conditions

factors determining channel shape:

• ligand gated channels
• voltage gated channels

Question 8

Voltage gated channels

Answer 8

• 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

Question 9

Exocystosis

Answer 9

• moving cells out of the cell

-

Question 10

Na+/K+ pump

Answer 10

• 1 ATP : 3 Na+ out : 2 K+ in

Question 11

Resting membrane potential

Answer 11

• close to -70mV
• membrane most permeable to K+
• efflux of K+ occurs until K+ is repelled by electromagnetic force
• reaches equilibrium

Question 12

Equilibrium Potential

Answer 12

• electrical work to repel outward cation diffusion = chemical work of diffusion down [ ] gradient
• nernst equation»_space;> ideal situation

Question 13

K+ equilibrium potential

Answer 13

• potential is -90mV

- only when no other species are involved

Question 14

Na+ equilibrium potential

Answer 14

• membrane most permeable to Na+ causes and influx of Na+
• at equilibrium, there is a net cation accumulation inside the membrane
• ENa+ = +60 mV

Question 15

Na+ channels

Answer 15

• 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)

Question 16

Action potential

Answer 16

• only produced where there are voltage gated Na+ channels (excitable membrane)
• depolarization causes surge towards 60 mV
• shuts off at 30 mV
• K+ leakage restores RP

Question 17

All or none principle

Answer 17

• a potential is either fired or not

- same magnitude for threshold and supra-threshold

Question 18

Frequency Coding

Answer 18

• stronger, longer lasting stimulus generates a burst of AP

Question 19

Refractory period

Answer 19

• period where some Na+ channels are inactivated
• channels stay inactivated until below threshold

Absolute RP- no channels reconfigured
Relative RP- some are reconfigured