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UVic BIOL 360 - Fall 2019 > Membranes + Transport (ch 10, 11) > Flashcards

Membranes + Transport (ch 10, 11) Flashcards

1
Q

In what 4 ways can lipids move in the membrane bilayer?

A
  1. Lateral diffusion
  2. Flexion
  3. Rotation
  4. Flip-flop (rare)
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2
Q

What are the 2 types of phospholipids?

A
  1. Phosphoglycerides

2. Sphingolipids

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3
Q

What are the 3 most common types of phosphoglycerides?

A
  1. Phosphatidyl-choline (eukaryotes)
  2. Phosphatidyl-ethanolamine (prokaryotes)
  3. Phosphatidyl-serine
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4
Q

Describe the structure of a phosphoglyceride.

A

Two fatty acid tails connected to a phosphate group by glycerol.

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5
Q

Describe the structure of a sphingolipid.

A

One fatty group (not acid) connected to a phosphate group by sphingosine. Potential to add a fatty acid.

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6
Q

What is the resulting structure called when another sphingosine is added to an existing sphingolipid?

A

Sphingomyelin.

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7
Q

Describe the structure of a sterol.

A

Solid carbohydrate rings with small polar head group and non-polar hydrocarbon tail.

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8
Q

How can cholesterol in a membrane be beneficial?

A

Can act as a temperature buffer by stabilizing the membrane at extremely high or low temperatures.

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9
Q

Do prokaryotes have cholesterol? How do they protect against temperature fluctuations?

A

No, but they have other sterols which accomplish the same function.

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10
Q

Describe the structure of a glycolipid. Where on the membrane are they localized?

A

One fatty chain and one fatty acid connected to a sugar by sphingosine. Always on the exterior of the membrane.

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11
Q

How are archael lipids different from eukaryotic/prokaryotic lipids?

A

Archael: branched, ether-linked, monolayer

Pro-/Eukaryotes: unbranched, ester-linked, bilayer

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12
Q

In human cells, how many different types of lipids are there (give a range)?

A

Between 500 and 2000 types.

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13
Q

How does the ratio of saturated and unsaturated fatty acids in the bilayer change with temperature? What enzyme accomplishes the conversion?

A

Increased unsaturation in cold because of their looser association, keeping membrane fluid. Saturation/unsaturation done by enzyme desaturase.

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14
Q

Why is asymmetry of the lipid bilayer important?

A

Critical for cell recognition, apoptosis signalling, membrane protein function, etc.

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15
Q

What is the purpose of inositol phospholipids?

A

Involved in signalling pathways. They allow proteins to dock to the membrane.

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16
Q

Do eukaryotic cells ever have lipid monolayers? In what capacity?

A

Yes. Monolayers are used in storage vesicles/micelles for hydrophobic molecules. Often associated with the ER.

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17
Q

What 2 factors implicit to the association of proteins with the membrane affect protein function?

A
  1. Method of association

2. Location on the membrane

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18
Q

How are transmembrane proteins associated with the membrane?

A

They have a hydrophobic domain (or multiple) which crosses the membrane.

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19
Q

What is the purpose of β-barrels in the membrane?

A

Act as pores/channels for molecules to cross.

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20
Q

What are the 3 lipid anchors for lipid-anchored membrane proteins?

A
  1. myristoyl anchor
  2. palmitoyl anchor
  3. farnesyl anchor
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21
Q

What linkage allows a myristoyl anchor to bind a membrane protein? Is it reversible?

A

An amide linkage. Stable/irreversible.

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22
Q

What linkage allows a palmitoyl anchor to bind a membrane protein? Is it reversible?

A

A thioester linkage. Reversible.

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23
Q

What linkage allows a farnesyl anchor to bind a membrane protein? Is it reversible?

A

A thioether linkage (as in methionine). Stable/irreversible.

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24
Q

What is a glycoprotein?

A

A membrane bound protein with an attached sugar on the extracellular side of the membrane.

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25
Q

What differentiates the bound sugar of a proteoglycan from that of a glycoprotein?

A

Proteoglycan: long sugar with no branching, sugars added 1 at a time
Glycoprotein: branched sugars added 14 at a time

26
Q

On which side of the membrane do integrated proteins have disulfide bonds? What about sulfhydryl groups?

A

Disulfide bonds = exterior

Sulfhydryl groups = interior

27
Q

How can protein mobility in the lipid membrane be restricted?

A

By tight junctions or because of functional limitation.

28
Q

How can proteins maintain their position in the membrane?

A

By forming complexes with anchored proteins, anchoring to cytoskeleton or extracellular matrix.

29
Q

What are some characteristics of a lipid raft?

A
  • Higher than normal cholesterol
  • More GPI-anchored proteins
  • More sphingolipids
  • Slightly thicker membrane
30
Q

How can the shape of a membrane be controlled?

A

Through the integration of membrane-bending proteins which modify the bilayer to a desirable shape.

31
Q

How do small hydrophobic molecules move across membranes?

A

Diffusion.

32
Q

How do inorganic ions and small organic polar molecules move across membranes?

A

Transporters/Channels.

33
Q

How do large macromolecules move across membranes?

A

Endo-/exocytosis.

34
Q

What are the 2 types of passive transport?

A
  1. Channel-mediated

2. Transporter-mediated

35
Q

What differentiates the kinetics of a transporter from the kinetics of a channel?

A

Transporter: has a max saturation (transport rate)
Channel: no max saturation (transport rate)

36
Q

What are the 3 types of active transporters?

A
  1. Coupled transporters
  2. ATP-driven pump
  3. Light-driven pump
37
Q

What differentiates a symporter from an antiporter?

A

Symporter: 2 molecules are moved together in the same direction
Antiporter: 2 molecules move in opposite directions for transport

38
Q

What are the 3 types of ATP-driven pumps?

A
  1. P-type pump
  2. ABC transporter
  3. V-type pump / F-type ATP synthase
39
Q

How are the functions of a V-type pump and an F-type ATP synthase linked?

A

V-type: uses ATP to move protons out of the cell

F-type: moves protons into the cell to produce ATP

40
Q

What is required for a P-type ATPase to function?

A

ATP must be used to facilitate (anti)transport of molecules.

41
Q

How do ABC transporters work?

A

Use 2 ATP to move solute molecules into/out of the cell.

42
Q

What does the ABC in ABC transporter stand for?

A

ATP-binding casette.

43
Q

How do prokaryotes use ABC transporters differently than eukaryotes?

A

Prokaryotes: for import and export
Eukaryotes: mainly for export

44
Q

What are the 4 main characteristics of ion channels?

A
  1. Always passive
  2. Have high ion selectivity
  3. Super high efficiency
  4. Gated (open or closed)
45
Q

What are the 4 types of ion channels?

A
  1. Voltage-gated
  2. Ligand-gated (extracellular ligand)
  3. Ligand-gated (intracellular ligand)
  4. Mechanically gated
46
Q

How is the membrane potential in animal cells created?

A

Through the movement of Na+ and K+ ions across the membrane through diffusion or transport.

47
Q

How many of ions are moved across the membrane by an Na+/K+ exhanger per molecule of ATP?

A

3 Na+ out, 2K+ in.

48
Q

K+ diffuses via K+ leak channel according to chemical gradient until _______.

A

Membrane potential approaches 0 (never reaches neutral charge though).

49
Q

How is the K+ channel impermeable to Na+?

A

The K+ leak channel has a selectivity filter made up of carbonyl oxygens which can interact with the K+ ion (after hydrate shell lost) but not the Na+ ion.

50
Q

How come the Na+ ion channel is impermeable to K+ even though it is larger than the K+ channel?

A

The channel is large enough to allow the passage of Na+ with its hydrate shell but too small to allow passage of hydrated K+. Loss of K+ shell would be unfavourable though.

51
Q

What do aquaporins transport? What do they not transport?

A

Only water. Nothing else.

52
Q

How do aquaporins remain impermeable to ions?

A

Small enough that they only allow H20 to pass one at a time.

53
Q

How do aquaporins remain impermeable to protons?

A

Because of a double Asn region which breaks up the H20 chain (which would otherwise relay H+).

54
Q

Why do voltage-gated channels have lateral portals?

A

To allow the central cavity to be influenced by other factors (ex: hydrophobic drugs).

55
Q

What is the purpose of the inactivation gate on a voltage-gated channel?

A

Plugs the open state to facilitate membrane potential propagation (closes during refractory period).

56
Q

What differentiates patch current from aggregate current?

A

Patch: multiple small depolarizations
Aggregate: sum of the patch currents

57
Q

In a transmitter-gated ion channel, what is the purpose of an excitatory neurotransmitter?

A

Opens cation channels, depolarizes.

58
Q

In a transmitter-gated ion channel, what is the purpose of an inhibitory neurotransmitter?

A

Opens K+ or Cl- channels, repolarizes.

59
Q

What is an example of a transmitter-gated ion channel?

A

Neuron synapses.

60
Q

What might be the purpose of drugs which target (neuro)transmitter-gated ion channels?

A

Muscle relaxants, anti-depressants, insomnia/anxiety/schizophrenia treatments.

61
Q

Organize the following by how easily they cross a membrane, from easiest to hardest:
large polar molecules (glucose), small polar molecules (H₂O, urea), hydrophobic molecules (steroids, O₂), ions (Na⁺, Ca²⁺)

A
  1. hydrophobic molecules (steroids, O₂)
  2. small polar molecules (H₂O, urea)
  3. large polar molecules (glucose)
  4. ions (Na⁺, Ca²⁺)

UVic BIOL 360 - Fall 2019 (10 decks)

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