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BS202 > 15.2 Transport of Small Molecules > Flashcards

15.2 Transport of Small Molecules Flashcards

1
Q

concentration/ion gradients drive transport → no energy required (passive transport)

A

facilitated diffusion

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2
Q

what are the 2 classes of proteins that facilitate passive transport

A
  1. carrier proteins
  2. channel proteins
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3
Q

bind to molecules and then undergo conformational changes that allow the molecules to pass through the PM

A

carrier proteins

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4
Q

carrier proteins are involved in the facilitated diffusion of …

A
  1. sugars
  2. amino acids
  3. nucleosides
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5
Q

give a brief overview of how the glucose transporters work

A

function by alternating between 2 conformational states; glucose-binding site is alternately exposed on the outside and the inside of the cell

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6
Q

glucose concentration gradient across PM is maintained because (…) (i.e. intracellular glucose levels remain low)

A

glucose is rapidly metabolized in the cell

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7
Q

form open pores through the PM → allowing free diffusion of any molecule of the appropriate size and charge

A

channel proteins

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8
Q

what are the 2 major types of channel proteins

A
  1. aquaporins
  2. ion channels
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9
Q

channel proteins that allow rapid transport of water molecules, but are impermeable to charged ions

A

aquaporins

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10
Q

aquaporins generally function to …

A

increase flow of water across epithelial cell layers

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11
Q

in plants, aquaporins are involved in …

A

water transport up stems and transpiration regulating in leaves of plants

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12
Q

in humans, aquaporins …

A

maintain water balance in the brain and extrude sweat from skin

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13
Q

channel proteins whose opening and closing is responsible for rapid transmission of electric signals

A

ion channels

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14
Q

most ion channels are not permanently open → opening of ion channels is regulated by ‘()’ that transiently open in response to specific stimuli

A

gates

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15
Q

what are the 2 types of ion channels (based on gating mechanism)

A
  1. ligand-gated channels
  2. voltage-gated channels
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16
Q

ion channels that open in response to binding of neurotransmitters or other signalling molecules

A

ligand-gated channels

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17
Q

ion channels that open in response to changes in electric potential across PM

A

voltage-gated channels

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18
Q

main role of ion channels is (1) - involved in (2)

A
  1. transmission of electric impulses
  2. action potentials of neurons
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19
Q

how were action potentials first observed in giant squid axons?

A

electrodes inserted in squid axons measured the changes in membrane (electric) potential that take place during nerve impulse transmission

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20
Q

resting membrane potential of giant squid axons =

A

60 mV (-60 mV inside cell)

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21
Q

ion gradients driving transport through ion channels are established by ()

A

ion pumps

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22
Q

for giant squid axons, flow of () makes the biggest contribution to the resting membrane potential

A

K+

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23
Q

the relationship between ion concentration and membrane potential is given by the ()

A

Nernst eqn

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24
Q

contrast ion channels and carrier proteins

A
  • carrier proteins undergo conformational changes in order to transport molecules through the PM
  • ion channels form pores that allow the free passage of certain molecules across the membrane; gradients are often generated by ion pumps
25
Q

() travel along axons → causes rapid depolarization of PM due to the opening and closing of voltage-gated Na+ and K+ channels

A

nerve impulses (aka action potentials)

26
Q

nerve impulses (aka action potentials) travel along axons → causes rapid depolarization of PM due to opening and closing of()

A

voltage-gated Na+ and K+ channels

27
Q

() allows action potentials to travel the length of a nerve cell

A

depolarization of adjacent regions of PM

28
Q

arrival of action potentials at neuron terminus signals () which carry signals between cells at a synapse

A

release of neurotransmitters

29
Q

neurotransmitters then bind to receptors on another nerve cell to open ()

A

ligand-gated ion channels

30
Q

the () serve as a good model for studying action potentials involving ligand-gated ion channels

A

nicotinic acetylcholine receptors

31
Q

give an overview of how the nicotinic acetylcholine receptors function

A
  1. binding of acetylcholine on nicotinic acetylcholine receptors (on muscle cells) opens a channel that allows rapid influx of Na+
  2. channel opens because acetylcholine binding induces a conformational change in the receptor
  3. rapid depolarization of cell triggers action potential → leads to muscle contraction
32
Q

selectivity of Na+ channel can be explained in part on the basis of a ()

A

narrow pore that acts as a size filter (Na+ channel pore is too narrow for K+ or larger ions)

33
Q

selectivity of K+ channels is based on structural properties of K+ that allow it to ()

A

interact with carbonyl oxygen ions lining the channel

34
Q

explain how interaction with carbonyl oxygen ions lining the K+ ion channel allows it to be selective for K+ ions

A

K+ structure interacts with carbonyl oxygens to displace the H2O molecule to which K+ is bound → K+ ion passes through channel (Na+ is too small to interact with carbonyl oxygen and remains bound to water)

35
Q

in (), molecules are transported against their concentration gradients using energy provided by a coupled reaction (e.g. ATP hydrolysis)

A

active transport

36
Q

the () uses energy from ATP hydrolysis to exchange 3 Na+ and 2 K+ against their electrochemical gradients → driven by conformational changes in the pump

A

Na+ - K+ pump (aka Na+ - K+ ATPase)

37
Q

the Na+ - K+ pump (aka Na+ - K+ ATPase) uses energy from ATP hydrolysis to exchange () against their electrochemical gradients → driven by conformational changes in the pump

A

3 Na+ and 2 K+

38
Q

give an overview of the action of NaK ATPase

A
  1. 3 Na+ bind to sites exposed inside the cell
  2. binding of Na+ stimulates ATP-dependent phosphorylation of the pump
  3. phosphorylation exposes the Na+ binding sites to the cell surface and lowers their binding affinity, so that Na+ is released outside of the cell
  4. at the same time, 2 K+ bind to high-affinity sites exposed on the cell surface
  5. binding of K+ stimulates dephosphorylation of the pump
  6. pump then returns to its original conformation, releasing K+ into the cell
39
Q

gradients established by the NaK pump are necessary for:

A
  • propagation of electric signals in nerve and muscle cells
  • driving of active transport of other molecules
  • maintenance of osmotic balance and cell volume → prevents the net influx of water
40
Q

other ion pumps include:

A
  1. Ca2+ pump
  2. H+ pump
41
Q

the Ca2+ pump maintains low () using energy from ATP hydrolysis

A

intracellular Ca2+ concentrations

42
Q

largest family of membrane transporters consists of the ()

A

ABC transporters

43
Q

the ABC transporters are characterized by () (i.e. domains)

A

highly conserved ATP-binding cassettes

44
Q

ABC transporters are composed of:

A

composed of 2 ATP-binding domains and 2 transmembrane domains

45
Q

in prokaryotes, ABC transporters transport () into the cell

A

nutrient molecules

46
Q

in both prokaryotes and eukaryotic cells, ABC transporters transport () outside of the cell

A

toxic substances

47
Q

susbstrate binding of ABC transporters alternates between () depending on ATP binding and hydrolysis

A

outward facing and inward facing

48
Q

susbstrate binding of ABC transporters alternates between outward facing and inward facing depending on ()

A

ATP binding and hydrolysis

49
Q

give an overview of the action of ABC importers

A
  • ATP-bound transporters face outward → substrate binds outside of the cell
  • ATP hydrolysis to ADP changes conformation so that the importer faces inwards to release substrate
50
Q

() results from defective Cl- transporters in affected epithelial cells

A

cystic fibrosis

51
Q

cystic fibrosis results from defective () in affected epithelial cells

A

Cl- transporters, specifically the cystic fibrosis transmembrane conductance regulator, CFTR (ABC transporter)

52
Q

first effective druge against cystic fibrosis; worked against mutant CFTR and increases Cl- transport

A

Kalydeco

53
Q

other molecules are transported against their concentration gradients by the coupled transport of ()

A

a second molecule in the energetically favored direction

54
Q

a transporter that transports 2 molecules in the same direction

A

symport

55
Q

explain how the Na+ gradient provides energy for active transport in epithelial cells

A
  1. epithelial cells use active-transport systems in the apical domains of their PMs to take up dietary sugars and amino acids from the intestinal lumen
  2. glucose uptake is carried out by a symporter that coordinately transports 2 Na+ ions for 1 glucose into the cell
  3. flow of Na+ down its electrochemical gradient drives transport of dietary glucose
  4. glucose is then released into underlying connective tissue (containing blood capillaries) at the basolateral surface of the epithelium
  5. transport of glucose is driven by concentration gradient (facilitated diffusion)
56
Q

transporter that transports a single molecule

A

uniport

57
Q

Na+ gradient is also involved in the action of the ff:

A
  1. Na-Ca transporter - exchanges Na+ for Ca2+
  2. Na-H exchange protein - exchanges Na+ for H+
58
Q

transporter that transports 2 molecules in different directions

A

antiporter

BS202 (36 decks)

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