exam 3 membrane channels and transporters

Question 1

what does movement of ions and small molecules across membranes require

Answer 1

the use of channel and transporter proteins

Question 2

what does passive transport involve

Answer 2

the movement of a solute down its concentration gradient - does not require energy input

Question 3

what is active transport

Answer 3

the movement of a solute up a concentration gradient - requires energy input

Question 4

where can energy come from

Answer 4

ATP, the movement of something down a gradient, or from high energy electrons

Question 5

what are molecular pumps

Answer 5

the transporters involved in active transport

Question 6

what type of barriers are biological membranes

Answer 6

semipermeable barriers

Question 7

what molecules can/can’t cross membranes freely

Answer 7

nonpolar molecules can diffuse freely, but polar/charged solutes are unable to cross without assistance

Question 8

what do transmembrane proteins channels and transporters allow

Answer 8

allow polar/charged solutes to cross membranes

Question 9

what do channels do

Answer 9

allow diffusion down a concentration gradient when channel is open

Question 10

what do transporters do

Answer 10

use conformational changes to move substances across the membrane and may transport down (passive transport) or up (active transport) a concentration gradient

Question 11

what is diffusion

Answer 11

movement of charged solute down a concentration gradient

Question 12

what is a concentration gradient

Answer 12

difference in concentration of a solute/solvent in one region compared to another

Question 13

what does the movement of any molecule or ion moving up/down a concentration gradient require

Answer 13

change in free energy

Question 14

what is an electrochemical gradient

Answer 14

sum of concentration gradient and electrical gradient

Question 15

what can delta G (change in free energy) tell us

Answer 15

whether a substance will move passively (no energy needed) or actively (energy input required) across a membrane

Question 16

what happens if delta G is negative

Answer 16

moves passively

delta G = max amount of energy available to drive another diffusion of solute

Question 17

what happens if delta G is positive

Answer 17

energy required - active

delta G = the amount of energy required to move a mole of solute up its electrochemical gradient and into the cell

Question 18

what is simple diffusion

Answer 18

diffusion across lipid bilayer (independent of proteins - no assistance needed)

Question 19

what is simple diffusion limited by

Answer 19

polarity, charge, size

highly polar, charged, and large can’t move across membrane

Question 20

what is permeability

Answer 20

the ability of the membrane to maintain concentration differences between the internal and external environments

Question 21

what are transport proteins

Answer 21

proteins that move small molecules and ions across membranes

Question 22

what is the difference between simple and transporter-mediated diffusion

Answer 22

simple is in either direction and can NOT be saturated

transporter is directional and saturable

Question 23

are transporters and channels active or passive

Answer 23

channels are always passive

transporters can be passive or active (active are pumps)

Question 24

what are ion channels

Answer 24

move ions and water across membrane

Question 25

what is a channel

Answer 25

protein across membrane that allows the net flux of specific ions across a membrane down their electrochemical gradients only

Question 26

what is the difference between channels and transporters

Answer 26

channels do NOT need to change their conformation to move each ion across the membrane (can maintain solute fluxes)

Question 27

what is the structure of channels

Answer 27

one or more membrane-spanning protein subunits surrounding a central pore lined with hydrophilic R groups

Question 28

how are ion channels highly selective

Answer 28

most allow only one type of ion to pass through

Question 29

where does ion selectivity occur

Answer 29

the pore consists of a double funnel with wide openings at the surfaces of the membrane and a narrow region further in the lipid bilayer

Question 30

what are ion channels regulated by

Answer 30

a central pore that can be gated open and shut by conformational changes

Question 31

what can changes in conformation be driven by (channels)

Answer 31

- ligand-gated channels: the binding of ligands to the channel - voltage-gated channels: changes in membrane potential - mechanosensitive channels: distortion of the bilayer - temperature-sensitive channels: temp

Question 32

what is active transport

Answer 32

movement of solutes up their electrochemical gradients

Question 33

what can active transport create and maintain

Answer 33

concentration gradients of solutes across membranes

Question 34

how can active transport directly contribute to membrane potentials

Answer 34

if the transported solutes carry a net charge across the membrane

Question 35

what are the three types of active transport

Answer 35

ATP-ase pumps, pumps that use diverse energy sources, coupled transporters

Question 36

what are ATP-ase pumps

Answer 36

pumps that use ATP hydrolysis to move solute

Question 37

what are coupled transporter

Answer 37

link the movement of one solute up its electrochemmical gradient to the movement of another solute down its electrochemical gradient. their energy source is an existing electrochemical gradient

Question 38

what are the three classes of ATP pumps

Answer 38

P-type pump, F/V-type pumps, and ABC transportres

Question 39

what are P-type pumps

Answer 39

when it hydrolyzes ATP, it phosphorylzes the pump itself, causing conformation change to allow an ion to be pumped across membrane (phorphorylation-dephosphorylation cycle to allow cycle to happen) each pump only pumps one type of ion

Question 40

what are F/V-type pumps

Answer 40

sam machinery as P-type, but running in different directions

Question 41

what are ABC transporters

Answer 41

ATP-Binding-Cassette: instead of rotary motion, ATP binds to symmetric dimers where each one binds two molecules of ATP at same time, ATP hydrolysis causes opening and closing, pushing a proton up its gradient

Question 42

what does the P-type pump, calcium ATPase do

Answer 42

allows cell to detect small increase of calcium (can be used as signaling molecule)

Question 43

where are calcium ATPase pumps found

Answer 43

in ER and surface of cell - direction flows out of cytosol into other compartment

Question 44

what happens for every ATP molecule hydrolyzed with Calcium ATP-ase

Answer 44

can move one calcium ion - helps maintain low resting calcium concentration in cytosol

Question 45

what does the P-type pump, Na+/K+ pump do

Answer 45

it's an antiporter - for each cycle, it transports 3 Na+ out of a cell and 2 K+ into a cell (net charge of +1 out of the cell per cycle)

Question 46

how does the Na+/K+ pump work

Answer 46

it has specific binding sites for Na and K - each step in hydrolysis of ATP and binding of transported ion drives conformational chanes

Question 47

what is the F-type pump

Answer 47

uses a proton gradient to generate ATP - found in mitochondria and thylakoid membrane of chloroplast and in bacteria

Question 48

what is the V-type pump

Answer 48

regulates pH of environment by pumping H+ into lysosomes, synaptic vesicles, and plant vacuoles

Question 49

how is V-type pump different than F-pump

Answer 49

V-type energy causes rotary motion, moving proton across membrane - F-type is reverse and is converted into ATP synthesis

Question 50

what does a bacterial ABC transporter do

Answer 50

transports nutrients into cell and binds to ATP causing a conformational change - then is hydrolyzed and released, opening transporter

Question 51

what does a eukaryotic ABC transporter do

Answer 51

exports substances out of cells - works like bacterial, but in opposite direction

Question 52

what do MDR proteins do

Answer 52

multi-drug resistance proteins - expel toxic substances from cell (overexpressed in cancer cells to resist therapeutics)