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UVic BIOL 360 - Fall 2019 > Vesicular Transport (ch 13) > Flashcards

Vesicular Transport (ch 13) Flashcards

1
Q

What are the 3 intracellular vesicular transport pathways?

A
  1. Biosynthetic secretory pathway
  2. Endocytic pathway
  3. Retrieval pathway
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2
Q

What are the 3 major characteristics of vesicular traffic?

A

Vesicular traffic is:

  1. Organized
  2. Balanced
  3. Selective
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3
Q

What is the structure of phosphatidylinositol (PI)?

A

2 fatty acid chains bound to glycerol which is in turn attached to a phosphate head group.

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4
Q

What is the structure of a phosphoinositide (PIP)? What differentiates PI(3)P from PI(4)P?

A

A 6-member ring connected to a glycerol with 2 fatty acid tails by a phosphate group. 3 and 4 denote different locations of phosphorylation on the ring.

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5
Q

On the phosphate head group of a phosphoinositide, which carbons do not allow phosphorylation?

A

Carbons 2 and 6 cannot be phosphorylated, only 3, 4, and 5. Carbon 1 is attached to the glycerol and thus can’t be phosphorylated either.

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6
Q

Where are phosphoinositides and phosphotidylinositol found on the plasma membrane?

A

Always on the cytosolic side.

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7
Q

What percentage of membrane lipids are phosphotidylinositol or phosphoinositides?

A

~10% of membrane lipids.

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8
Q

What are the 3 coat proteins we went over in lecture?

A
  1. Clathrin
  2. COP1
  3. COP2
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9
Q

What 2 functions does a coat protein perform?

A
  1. Shape/mold the vesicle

2. Concentrate specific proteins in the vesicle

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10
Q

Why would we want to change the phosphorylation status of phosphoinositides (PIPs)?

A

To change the recognition pattern of other proteins and bind selectively.

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11
Q

What is the structure of clathrin?

A

A three-legged “triskelion” structure with 3 light chains and 3 heavy chains.

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12
Q

How can clathrin associate with a membrane to form a vesicle?

A

Requires an adaptor protein which is specific to each membrane and facilitates binding.

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13
Q

During vesicular transport, what chaperone protein acts as an ATPase and is responsible for removing the clathrin coat from a vesicle?

A

Hsp70 chaperone.

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14
Q

During vesicular transport, what protein in responsible for budding and separation of a vesicle from a membrane?

A

Dynamin (+associated proteins).

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15
Q

Where do clathrin-coated vesicles travel to?

A

From the plasma membrane to the early endosome then the late endosome.

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16
Q

Where do COP1-coated vesicles travel to?

A

From the golgi to the endoplasmic reticulum, OR the early endosome to the plasma membrane.

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17
Q

Where do COP2-coated vesicles travel to?

A

From the endoplasmic reticulum to the golgi, OR the golgi to secretory vesicle/late endosome/plasma membrane.

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18
Q

What is the function of a phosphoinositide (PIP)?

A

To be recognized by adaptor proteins during early vesicle formation.

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19
Q

What happens to phosphoinositides (PIPs) when they are bound by an adaptor protein? What causes this?

A

They are depleted by PIP phosphatase.

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20
Q

How does a BAR domain dimer facilitate vesicle formation?

A

It helps to deform the membrane via electrostatic interactions.

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21
Q

What are the 2 coat-recruitment GTPases?

A
  1. Arf1 (adenosine diphosphate ribosylation factor 1) protein
  2. Sar1 (secretion-associated RAS-related) protein
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22
Q

Which coat protein is Sar1 (GTPase) associated with?

A

COP2 coat assembly.

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23
Q

How are the coat-recruitment GTPases activated? How are they de-activated?

A

They are activated by GEF phosphorylation and deactivated by GAP dephosphorylation.

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24
Q

Which coat protein is Arf1 (GTPase) associated with?

A

COP1 and Clathrin coat assembly.

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25
Q

What happens to the alpha-helix binding domain of Arf1 and Sar1 when GTP is bound?

A

The binding domain is exposed with GTP and hidden with GDP.

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26
Q

What 3 steps can outline vesicle delivery to a membrane?

A
  1. Tethering
  2. Docking
  3. Fusion
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27
Q

What purpose does the Rab effector protein serve during vesicle “tethering”? What protein does it bind to?

A

It binds Rab-GTP on the surface of the vesicle and begins pulling the vesicle toward the membrane.

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28
Q

What purpose do the t-SNARE proteins serve during vesicle “docking”? What protein do these bind to?

A

They bind to v-SNARE on the surface of the vesicle and squeeze out intervening water, locking the vesicle into place on the membrane.

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29
Q

How does a “docked” vesicle fuse with a membrane and deliver its cargo? What protein is important for this?

A

Rab-GDP dissociation inhibitor removes Rab-GDP from the vesicle membrane, allowing the vesicle to fuse with the membrane.

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30
Q

What happens to the v-SNARE once the vesicle has fused with the target membrane? How is it recycled?

A

It exists as a complex with t-SNARE. It is dissociated from the complex by NSF which is driven by ATP.

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31
Q

Under what circumstance would we want to pause vesicle transport just before vesicular fusion with the target membrane?

A

When we need to be able to deliver substrate immediately and on demand. Ex: in the synaptic cleft of the neuromuscular junction.

32
Q

What differentiates homotypic and heterotypic membrane fusion?

A

Homotypic: both membranes are of the same type
Heterotypic: both membranes are of different types.

33
Q

Are all proteins in the endoplasmic reticulum packaged into vesicles? Please elaborate.

A

No. Resident ER proteins and chaperone proteins remain in the ER.

34
Q

Why is it necessary to have different protein coats like COP1 and COP2?

A

For target specificity.

35
Q

How does the body retrieve proteins that were not supposed to leave the endoplasmic reticulum?

A

KDEL receptors which bind ER resident proteins are transported to the Golgi, picking up proteins. Once bound, they travel back to the ER.

36
Q

To make ER resident protein retrieval possible, what coat protein must KDEL receptors bind to?

A

Affinity for COP1 coat proteins which can transport them back to the endoplasmic reticulum.

37
Q

Why must the affinity of KDEL receptors for ER resident proteins be different in the Golgi vs the endoplasmic reticulum?

A

Don’t want KDEL binding to ER resident proteins in the ER and impeding their function. Only bind in Golgi.

38
Q

How many stacks comprise the Golgi apparatus in animals? What group of organisms possesses the largest Golgi?

A

Animals have 6 stacks, but some protists can have more than 60!

39
Q

Which Golgi face is closest to the Endoplasmic Reticulum?

A

The Cis face.

40
Q

What is the function of the cis Golgi network?

A

To phosphorylate oligosaccharides on lysosomal proteins.

41
Q

What is the function of the cis cisterna of the Golgi?

A

To remove Man.

42
Q

What is the function of the medial cisterna of the Golgi?

A

To remove Man and to add GlcNAc.

43
Q

What is the function of the trans cisterna of the Golgi?

A

To add Gal and NANA.

44
Q

What is the function of the trans Golgi network?

A

To sulfate tyrosines and carbohydrates.

45
Q

To what 3 locations are vesicles usually transported after leaving the trans Golgi network?

A
  1. Lysosome
  2. Plasma membrane
  3. Secretory vesicle
46
Q

How many Golgi apparati do animal cells have? What about plant cells?

A

Animals: one
Plants: lots

47
Q

How can we observe the local protein specificity of the Golgi apparatus?

A

By labeling the stacks with gold.

48
Q

Describe the cisternal maturation model of Golgi function.

A

Vesicles are delivered to the cis stack, which then moves through the golgi apparatus until being split into vesicles when it reaches the trans face. Vesicular transport in reverse.

49
Q

Describe the vesicle transport model of Golgi function.

A

The Golgi stacks are static, and vesicles move between stacks as they progress from one Golgi face to the other (bidirectional)

50
Q

In what manner are sugars added to a proteoglycan? What organelle accomplishes this?

A

The Golgi apparatus adds these sugars one at a time.

51
Q

Where do complex oligosaccharides get modified?

A

Precursor oligosaccharides are added to proteins in the ER, but must then be moved to the Golgi for complex modifications.

52
Q

In the Golgi, what enzymes facilitate complex oligosaccharide modification?

A

Glycosyl transferases.

53
Q

What are the 4 main purposes of glycosylation?

A
  1. Determine protein folding
  2. Protect protein from enzymes
  3. Regulate cell-surface signalling
  4. Protect protein from pathogens
54
Q

What characteristic must lysosomal membrane proteins have?

A

Must be highly glycosylated to prevent breakdown by acid hydrolases.

55
Q

What is the plant cell equivalent to a animal cell lysosomes?

A

A large, central vacuole.

56
Q

What is the purpose of a lysosome in an animal cell? What enzyme helps accomplish this?

A

To break down cellular components for recycling. Acid hydrolases catalyze breakdown.

57
Q

What prevents acid hydrolases from being active in the cytosol and indiscriminately breaking down cellular components?

A

They are inactive before post-translational modification in the lysosomes.

58
Q

How is the low pH inside lysosomes maintained?

A

Through the action of V-type ATPases which use ATP to pump H+ ions into the lysosome.

59
Q

What 4 pathways mentioned in class can deliver substrate to lysosomes?

A
  1. Phagocytosis
  2. Endocytosis
  3. Macropinocytosis
  4. Autophagy
60
Q

Describe endocytosis.

A

Form vesicle at the plasma membrane, engulfing nearby extracellular substrate.

61
Q

Describe pinocytosis. At what rate does this process proceed?

A

Membrane extends to “scoop” in extracellular fluid and substrate. ~2500/cell/minute.

62
Q

Is macropinocytosis spontaneous or non-spontaneous? Please elaborate.

A

Non-spontaneous. Requires signal activation at receptor.

63
Q

Is fluid-phase endocytosis spontaneous or non-spontaneous?

A

Spontaneous.

64
Q

What 2 methods exist for sorting membrane proteins in a polarized epithelial cell?

A
  1. Direct sorting in the trans Golgi network

2. Indirect sorting via early endosomes

65
Q

What are the 2 main functions of phagocytosis?

A
  1. Feeding (esp. Protists)

2. Immune response (engulf shit)

66
Q

Is phagocytosis spontaneous or non-spontaneous? Please elaborate.

A

Non-spontaneous. Must be induced by Rho-GTPases.

67
Q

What 3 main steps outline phagocytosis?

A
  1. Rho-GTPases signals PI kinase
  2. PI kinase accumulates PI(4,5)P₂
  3. Accumulation signals actin polymerization
68
Q

How is the signal which activates phagocytosis deactivated?

A

PI(4,5)P₂ is converted to PI(3,4,5)P₃, initiating depolymerization of actin.

69
Q

Describe exocytosis.

A

Transport out of the cell via vesicles.

70
Q

In what 3 ways can protein sorting occur in the trans Golgi network? Which of these occurs only in secretory cells?

A
  1. Signal-mediated diversion to lysosomes
  2. Constitutive secretory pathway
  3. Signal-mediated diversion to vesicles (for secretion) SECRETORY CELLS ONLY
71
Q

What might be the advantages of proteolytic processing (post-translational modification)?

A

To ensure that proteins remain inactive until they reach their destination and to increase cargo concentration.

72
Q

What 6 steps outline secretion at synaptic vesicles?

A
  1. Components delivered to synaptic membrane
  2. Endocytosis of components for new vesicle
  3. Delivery of vesicle to endosome
  4. New vesicle buds from endosome
  5. Neurotransmitter loaded into vesicle
  6. Exocytosis in response to action potential
73
Q

What 5 steps outline the special vesicle fusion which occurs with synaptic vesicles? What ion triggers fusion?

A
  1. Docking
  2. Priming 1
  3. Priming 2
  4. Fusion pore opening (triggered by Ca2+)
  5. Fusion complete
74
Q

What are the 3 main characteristics of a lysosomal protein?

A
  1. Cotranslationally moved to ER
  2. N-terminal signal directs to ER
  3. Additional signal directs to lysosome
75
Q

What is the pH in the cytosol? What about in the lysosome?

A

Cytosol: 7.2
Lysosome: 5.0

76
Q

What protein blocks SNARE from completing vesicle fusion in the synapse? What signal triggers the removal of this protein?

A

Complexin blocks SNARE bundles, but is removed when intracellular [calcium] increases.

77
Q

What are Arf1 (adenosine diphosphate ribosylation factor 1) protein and Sar1 (secretion-associated RAS-related) protein?

A

Coat-recruitment GTPases.

UVic BIOL 360 - Fall 2019 (10 decks)

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