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BSCI330 SPRING > exam 3 membrane channels and transporters > Flashcards

exam 3 membrane channels and transporters Flashcards

1
Q

what does movement of ions and small molecules across membranes require

A

the use of channel and transporter proteins

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2
Q

what does passive transport involve

A

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

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3
Q

what is active transport

A

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

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4
Q

where can energy come from

A

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

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5
Q

what are molecular pumps

A

the transporters involved in active transport

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6
Q

what type of barriers are biological membranes

A

semipermeable barriers

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7
Q

what molecules can/can’t cross membranes freely

A

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

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8
Q

what do transmembrane proteins channels and transporters allow

A

allow polar/charged solutes to cross membranes

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9
Q

what do channels do

A

allow diffusion down a concentration gradient when channel is open

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10
Q

what do transporters do

A

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

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11
Q

what is diffusion

A

movement of charged solute down a concentration gradient

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12
Q

what is a concentration gradient

A

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

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13
Q

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

A

change in free energy

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14
Q

what is an electrochemical gradient

A

sum of concentration gradient and electrical gradient

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15
Q

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

A

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

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16
Q

what happens if delta G is negative

A

moves passively

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

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17
Q

what happens if delta G is positive

A

energy required - active

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

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18
Q

what is simple diffusion

A

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

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19
Q

what is simple diffusion limited by

A

polarity, charge, size

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

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20
Q

what is permeability

A

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

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21
Q

what are transport proteins

A

proteins that move small molecules and ions across membranes

22
Q

what is the difference between simple and transporter-mediated diffusion

A

simple is in either direction and can NOT be saturated

transporter is directional and saturable

23
Q

are transporters and channels active or passive

A

channels are always passive

transporters can be passive or active (active are pumps)

24
Q

what are ion channels

A

move ions and water across membrane

25
Q

what is a channel

A

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

26
Q

what is the difference between channels and transporters

A

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

27
Q

what is the structure of channels

A

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

28
Q

how are ion channels highly selective

A

most allow only one type of ion to pass through

29
Q

where does ion selectivity occur

A

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

30
Q

what are ion channels regulated by

A

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

31
Q

what can changes in conformation be driven by (channels)

A
  • 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
32
Q

what is active transport

A

movement of solutes up their electrochemical gradients

33
Q

what can active transport create and maintain

A

concentration gradients of solutes across membranes

34
Q

how can active transport directly contribute to membrane potentials

A

if the transported solutes carry a net charge across the membrane

35
Q

what are the three types of active transport

A

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

36
Q

what are ATP-ase pumps

A

pumps that use ATP hydrolysis to move solute

37
Q

what are coupled transporter

A

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

38
Q

what are the three classes of ATP pumps

A

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

39
Q

what are P-type pumps

A

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

40
Q

what are F/V-type pumps

A

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

41
Q

what are ABC transporters

A

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

42
Q

what does the P-type pump, calcium ATPase do

A

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

43
Q

where are calcium ATPase pumps found

A

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

44
Q

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

A

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

45
Q

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

A

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)

46
Q

how does the Na+/K+ pump work

A

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

47
Q

what is the F-type pump

A

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

48
Q

what is the V-type pump

A

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

49
Q

how is V-type pump different than F-pump

A

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

50
Q

what does a bacterial ABC transporter do

A

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

51
Q

what does a eukaryotic ABC transporter do

A

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

52
Q

what do MDR proteins do

A

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

BSCI330 SPRING (24 decks)

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