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Biology 360 > Topic 3B - Transport Across Membranes > Flashcards

Topic 3B - Transport Across Membranes Flashcards

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1
Q

How do small hydrophobic molecules cross the membrane?

A

Diffusion

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2
Q

How do inorganic ions and small organic polar molecules cross the membrane?

A

Transporters and channels (may have a small amount of diffusion)

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3
Q

How do macromolecules cross the membrane?

A

Endocytosis and exocytosis

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4
Q

What two factors determine rates of diffusion?

A

Charge and size

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5
Q

Diffusion across a membrane absolutely cannot happen when a molecule is…

A

Charged

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6
Q

Define passive transport

A

Movement of particles in accordance with their concentration gradient

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7
Q

Define active transport

A

Movement of particles against their concentration gradient

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8
Q

Does diffusion have a maximum rate?

A

No

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9
Q

Does transporter-mediated diffusion have a maximum?

A

Yes - transporters can become saturated

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10
Q

What are the 3 kinds of active transport?

A
  1. Coupled transporters
  2. ATP-driven pumps
  3. Light-driven pumps
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11
Q

Define a symport

A

Both molecules being transported by a given transporter are moving the same way

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12
Q

Define an antiport

A

Two molecules are being moved by a transporter in opposite directions

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13
Q

In the lumen of the gut, glucose is packed into the cell by…

A

Coupled active transport of Na+ into the cell by a symport

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14
Q

What are the 3 kinds of ATP pumps?

A
  1. P-type
  2. ABC transporter
  3. V-type and F-type pumps
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15
Q

What is the difference between V-type and F-type transporters?

A

F-type synthesizes ATP and V-type uses ATP

Both are proton pumps, but they pump protons in opposite directions

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16
Q

What do ABC transporters move?

A

Small molecules like sugars, peptides, and ions

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17
Q

What do P-type pumps move?

A

Ions

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18
Q

What do V and F-type pumps move?

A

Protons

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19
Q

What are the 3 extracellular domains of P-type ATPases?

A
  1. Nucleotide binding domain
  2. Phosphorylation domain
  3. Activator domain
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20
Q

Give an example of a P-type ATPase

A

the Ca++ pump

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21
Q

In ATP driven pathways, at what point is ADP phosphorylated into ATP?

A

Never, always switched out

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22
Q

The Na+-K+ pump is a kind of (1)-type pump

A

P-type

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23
Q

How much of a cell’s energy is devoted to the Na/K+ pump?

A

1/3rd

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24
Q

Sodium inside the cell is…

A

Low

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25
Q

Potassium in the cell is in (high/low) concentration

A

High

26
Q

What does ABC (of ABC transporters) stand for?

A

ATP-binding cassette

27
Q

What is a key difference between eukaryotic and prokaryotic ABC transporters?

A

Pro: important for import and export
Euk: mostly important for export

28
Q

How many kinds of ABC transporters are there in mammals?

A

50-70

29
Q

What % of the E. coli genome codes for ABC transporters?

A

5%

30
Q

Why are ABC transporters implicated in cancer? (2)

A
  1. ABC remove drugs from the cancer cell so they are less responsive to treatment
  2. Cancer cells have a larger number of ABC transporters
31
Q

Most ABC transporters are (1)-directional

A

Unidirectional

32
Q

The largest family of membrane transporter proteins are…

A

ABC transporters

33
Q

What are 4 key characteristics of ion channels?

A
  1. High selectivity
  2. Gated pores
  3. High throughput rates
  4. Always use passive transport
34
Q

Is there such a thing as an active channel?

A

No! All channels use passive transport

35
Q

What are the 4 kinds of gating used by ion channels?

A
  1. Voltage-gated
  2. Ligand-gated (extracellular ligand)
  3. Ligand-gated (intracellular ligand)
  4. Mechanically gated
36
Q

In addition to voltage gating and ligand gating, this process can affect opening and closing of ion channels

A

Phosphorylation and dephosphorylation

37
Q

K+ diffuses via its channel according to its chemical gradient until…

A

Resting membrane potential is reached

38
Q

What 2 proteins are especially important in the establishment of the resting membrane potential?

A

K+ leak channels and the Na/K+ pump

39
Q

Why is the K+ channel impermeable for Na+? (2)

A
  1. Dehydrated Na+ cannot interact favourably with the carbonyl oxygens of the K+ selectivity filter - ENERGY BARRIER
  2. Na+ is too big to fit through the channel in a hydrated state
40
Q

A key residue in the selectivity for Na+ ions in the Na channel is…

A

E177

41
Q

Why is the Na+ channel wider than the K+ channel?

A

Na+ is transported with its water shell (partially hydrated), but K+ is too big in a partially hydrated state to pass through

42
Q

What is transported by aquaporins?

A

Water

43
Q

What is not transported by aquaporins?

A

Ions

44
Q

How many subunits make a functional aquaporin? (N = …)

A

N = 4

45
Q

How do aquaporins keep ions from passing through the channel?

A

1 side of the channel is hydrophobic. Since the channel is too narrow for hydrated ions to pass, and the energy cost to dehydrate these ions due to the hydrophobic layer is too large, ions do not cross the channel

46
Q

How do aquaporins keep protons from crossing the channel?

A

Disrupt the channel in the middle with two asparagine molecules which protons cannot travel across

47
Q

Why is the Na+ channel one single subunit?

A

At some point in evolutionary history the 4 subunits would have fused together

48
Q

What is the function of the lateral portals of the Na+ channel?

A

make the central cavity accessible from the hydrophobic core of the bilayer, pore blocking drugs (like anaesthetics) can block transmission through these

49
Q

What transmembrane domain(s) make up the voltage sensor of the Na+ channel?

A

S1-S4

50
Q

Where is the inactivation gate of the Na+ channel located?

A

In the S3-S4 loop

51
Q

What are the three states of the Na+ channel?

A
  1. Open
  2. Closed
  3. Inactivated
52
Q

In the key position of the inactivation gate, substituting F103 with other, larger aa will (increase/decrease) inactivation times

A

Increase - larger inactivation, more transient current

53
Q

What prevents backflow of propagation of APs?

A

Inactivation of Na+ channels

54
Q

The peak speed of an AP is…

A

100 m/s

55
Q

When different Na+ channels are open, how do their conductances differ

A

They do not, conductance of individual channels is the same

56
Q

When Na+ channels are depolarized equally and open, describe their rate of current

A

Rate of current constant

57
Q

What kinds of channels do excitatory neurotransmitters open?

A

Cation channels

58
Q

What kinds of channels do inhibitory neurotransmitters open?

A

Cl- or K+

59
Q

Which subunits on ach receptors bind the ligand?

A

alpha-subunits

60
Q

Describe the gate of ACh channels

A

Hydrophobic molecules keep ions from passing

61
Q

How does Prozac target ACh receptors?

A

Inhibits Na+ driven symports which clear neurotransmitter in the cleft for prolonged transmission

Biology 360 (12 decks)

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