Membrane Transport

Question 1

what is a key feature of the lipid bilayer

Answer 1

selectively permeable

Question 2

what does the lipid bilayer’s selective permeability permit

Answer 2

different conc of materials in the intra and extra cellular spaces

Question 3

what varies the permeability of smth through a membrane

Answer 3

• size
• charge
• polarity

Question 4

what is the permeability of small nonpolar molecules through the lipid bilayer

Answer 4

almost all goes through (tiny bit doesn’t)

Question 5

what is the permeability of small uncharged polar molecules through the lipid bilayer

Answer 5

some goes through, most is bounced off

Question 6

what is the permeability of large uncharged polar molecules through the lipid bilayer

Answer 6

most is bounces off (tiny lil bit can go through)

Question 7

what is the permeability of ions through the lipid bilayer

Answer 7

all is bounced off (none goes through)

Question 8

which two things cannot diffuse freely through a cell membrane

Answer 8

• ions
• polar molecules

Question 9

what assists the transport of ions and polar molecules

Answer 9

• channel proteins
• transporter (carrier) protein

Question 10

describe the trends of ions and their intra/extra cellular concentrations

Answer 10

everything is lower inside the cell than outside, except for K+

Question 11

what is passive transport

Answer 11

when molecules move from an area of high conc to low

Question 12

what is active transport

Answer 12

requires input of energy and can move molecules against their conc gradients

Question 13

what is another word for passive transport

Answer 13

diffusion

Question 14

passive diffusion is affected by what

Answer 14

• concentration
• charge

Question 15

the transport of uncharged molecules is primarily governed by what

Answer 15

concentration

Question 16

the transport of charged molecules is governed by what

Answer 16

• concentration
• voltage gradients

Question 17

water can move passively across the membrane down its concentration gradient how

Answer 17

osmosis

Question 18

what is hypertonic

Answer 18

water conc in < water conc out

Question 19

what is isotonic

Answer 19

water conc in = water conc out

Question 20

what is hypotonic

Answer 20

water conc in > water conc out

Question 21

is osmosis passive or active transport

Answer 21

passive

Question 22

what allows water to move more rapidly across a membrane

Answer 22

specialized channel proteins called aquaporins

Question 23

do cells have additional mechanisms to avoid osmotic swelling

Answer 23

some do

Question 24

how do protozoans avoid osmotic swelling

Answer 24

using contractile vacuoles that periodically discharge their contents to the exterior

Question 25

how do plant cells avoid osmotic swelling

Answer 25

touch cell walls can tolerate large osmotic differences (they fight the gradients)

Question 26

how do animal cells avoid osmotic swelling

Answer 26

use transmembrane pumps to expel solutes (like Na+ ions that tend to leak into the cell)

Question 27

what proteins help move materials across a membrane

Answer 27

- there are many types - each membrane has its own characteristic set of transport proteins

Question 28

when a substance is moving against the electrochemical gradient, what is needed

Answer 28

an input of energy

Question 29

what are gradient-driven pumps

Answer 29

transporters that facilitate the movement of 2 different molecules

Question 30

what is a symport gradient-driven pump

Answer 30

2 diff molecules being moved in the same direction

Question 31

what is an antiport gradient-driven pump

Answer 31

2 diff molecules being moved in opposite directions

Question 32

what kind of pump are transporters that move a single type of molecule via conc gradient

Answer 32

trick question: they are not considered pumps as no external energy is required

Question 33

can glucode diffuse passively in intestinal epithelial cells

Answer 33

- no - glucose conc is higher inside than in lumen or blood

Question 34

describe the Na+/glucose symport

Answer 34

- glucose conc is higher inside intestinal epithelial cells than in lumen or blood - so it cannot diffuse passively - Na+ is driven into the cell by the electrochemical gradient - glucose is actively transported into the cell by the symport (if Na+ is going in, then glucose need to too) - Na+ is actively transported out of the cell by the Na+/K+ pump to maintain the gradient needed

Question 35

what uses most of the energy in our bodies

Answer 35

Na+/K+ pump

Question 36

describe the steps in the Na+/K+ pump

Answer 36

- Na+ binds - pump phosphorylates itself, hydrolyzing ATP - phosphorylation triggers conformational change and Na+ is ejected - K+ binds - pump dephosphorylates itself - pump returns to original conformation and K+ is ejected

Question 37

what pump do animal and plant cells use to setup gradients that drive the movement of ions and soluted

Answer 37

Na+ pump

Question 38

what are channel proteins

Answer 38

aqueous pores that allow passive movement of small, water soluble molecules across a membrane

Question 39

are channel proteins selective

Answer 39

- yes, they are selective for a particular ion - based on size, shape, distribution of charged amino acids

Question 40

are channel proteins continuously open

Answer 40

- most are gated, requiring stimulus to switch between open and closed

Question 41

what channels are needed for nerve cells

Answer 41

- voltage-gated channels - distribution of ions on either side of the membrane gives rise to the membrane potential

Question 42

describe how K+ leak channels work

Answer 42

- high internal conc of K+ is maintained by Na+/K+ pump - K+ also moves across membranes through K+ leak channels - it is drawn into the cell to balance neg changed macromolecules (also leaks out down its conc gradient until electrochemical equilibrium is reached)

Question 43

are K+ leak channels uni or bi direction

Answer 43

bi directional

Question 44

what is a large contributor to the potential difference across membranes

Answer 44

K+

Question 45

describe how an action potential occurs in nerves

Answer 45

- resting potential of -60mv - a stimulus increasing the charge to -40mv, and an action potential occurs - voltage-gated Na+ channels are opened and ions rush in, increasing the charge to +40 - Na+ channels then close and are briefly inactivated - K+ moves out of the cell, repolarizing the membrane

Question 46

what happens when a nerve signal reached the terminal

Answer 46

- Ca2+ channels open - the influx of ions causes vesicles to fuse w the plasma membrane - neurotransmitters stores in vesicles are released into the synaptic cleft - neurotransmitters bind to channel proteins on adjacent cells - these channels open and ions flow into the cell, making a membrane potential

Question 47

describe how channel proteins work for hearing

Answer 47

- ears have stereocilia which vibrates in response to sound - these movements cause the mechanically-gated ion channels to open, eliciting a response