protein channels

Question 1

do not require energy but rely on conformational changes

Answer 1

uniporter, symporter and anitporter

Question 2

membrane permeability coefficient of large uncharged solutes and charged solutes

Answer 2

low membrane permeability coefficient

Question 3

ion channesl

Answer 3

passive transport of ions
-down their electrochemical gradients (charge and concentration gradients)

Question 4

why is the rate of ion movement thorugh an ion channels much faster than the rate via a uniporter

Answer 4

channles form a hydrophilic passageway through which multiple ions can move, simultaneously

Question 5

forms a pore through membranes

Answer 5

membrane proteins

Question 6

what are the two types of membrane channel

Answer 6

open- ex, porin
gated- closed channel that can be opened, is selective

Question 7

what type of channels are most channels

Answer 7

gated

Question 8

opening and closing triggered by change in membrane potential

Answer 8

voltage gated

Question 9

opening and closing triggered by binding of a ligand to the channel protein

Answer 9

ligand gated

Question 10

opennig and closing triggered by distortions in the cell shape (contraction)

Answer 10

mechanical or stretch gated

Question 11

what type of gated channel is the sodium channel

Answer 11

voltage gated

Question 12

channel structure of voltage gated channel

Answer 12

-hydrophobic R group on the outside interact with lipids
-polar peptide bond regions on the inside form aqueous channel
-cytoplasmic loop acts as a gate
-one helice in each segment acts as a voltage sensor

Question 13

what do ion channesl consist of

Answer 13

-gate which opens and closes based on membrane potential
-sectivity filter that selects ion type
-voltage sensing helix detects change in membrane potential

Question 14

operation of an ion channel

Answer 14

change in membrane potential causes shift in positively charged sensor helix which causes gate to open

Question 15

voltage gated channels in an axon steps

Answer 15

1.membrane resting potential of -60mv
2. local depolarization/ change in membrane potential triggrers opening of nearby Na channesl leading na to flow in and membrane potential becomes +30mv
3. +30 potential cuases na channels to close and K channesl to open and k flows out and reestablishes negative potential of -75mv
4. -75mv potential caues k channesl to close and pump kick in to reestablish ion gradients

Question 16

more na or k inside or outside

Answer 16

more na outside more k inside

Question 17

T/F outside negative electric potential of 60-70 mv exists across all plast membranes

Answer 17

Flase bc its insdie thats negative

Question 18

T/F- K resting channesl are nongated ion channels

Answer 18

true

Question 19

the membrane potential in animal cells depends largely on resting k channels, how do these channesl achieve selectivity for k versus na which is actually smaller than k

Answer 19

k channels interact with 8 carbonyl oxygen atoms lining the channle resulting in a low activation energy to move into the channel

na ions cannot perfectly bind to the channl oxygen atoms

na remians hydrated and therefor needs a larger activation energy to move into the channel

Question 20

what are ligand gated ion channles used for

Answer 20

in neurons when neurotransmitters are released at the synaptic cleft

Question 21

where and when are stretch gated channels used

Answer 21

less common
used in sensory nerves

Question 22

required the distortion in membrane that triggers opening of the gate

Answer 22

stretch gated channels
-tension in membrane casuses confrmational change

Question 23

aquaporins

Answer 23

seelctive transport
-several narrow passages minimally larger than water
-pores form H bonds with water molecuels
-ions and solutes do not move through
there is a central pore and 4 pores

Question 24

where does water move through in aquaporins

Answer 24

thorugh the narrow passages in each monomer not the central pore

Question 25

speed of water moveemnt in aquaporins

Answer 25

3 billion water per second

Question 26

T/F four monomers arrange to form a central pore for water to move through

Answer 26

false

Question 27

T/F hydrophilic aa residues from hdyrogen bonds with water molecules

Answer 27

true

Question 28

T/F aquaporins contain a water selective gate that prevents tranpsort of large solutes but allow movement of water, protons and other ions

Answer 28

false

Question 29

tranport of non water molecules in aquaporins

Answer 29

ability to transport a variety of molecules
-non water trnapsort often associated with alterations (physical tention/ phosphorylation)
-possible transport is thorugh the central pore

Question 30

pumping ions stats

Answer 30

hundreds of pumps per cells each capable of moving thousands of ions per min

Question 31

how much of a cells energy is devoted to moving ions

Answer 31

depenidng on the cell 50+% of the cells total energy

Question 32

what are the specialized functions of cells that required pumps

Answer 32

muscle contraction, nerve impulse generation, etc