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BMS2.16 Vesicle Trafficking > Vesicle Trafficking > Flashcards

Vesicle Trafficking Flashcards

1
Q

Free ribosomes:

A
  • located in cytosol
  • site of protein synthesis for proteins that remain in the cell
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2
Q

Protein transfer/delivery to all organelles except the ER occurs when?

A
  • post-translationally
  • follows synthesis on free ribosomes in the cytosol
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3
Q

Protein transfer/delivery to all organelles except the ER is mediated by:

A
  • Organelle-specific amino acid sequences in proteins.
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4
Q

________ targets proteins to different organelles.

A

Unique amino acid sequences in the proteins

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5
Q

How many proteins compose the nuclear pore?

A

about 30

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6
Q

Proteins enter and leave the nucleus through:

A

nuclear pores (bi-directional)

  • mRNA also leaves the nucleus through nuclear pores
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7
Q

Steps in the transport of nuclear proteins to the nucleus from the cytoplasm:

A
  1. nuclear proteins have a nuclear localization sequence in their amino acid sequence.
  2. cytoplasmic protein importin binds to nuclear localization sequence.
  3. importin/nuclear protein complex moves across nuclear pore.
  4. Ran-GTP releases importin from the nuclear protein in the nucleus.
  5. importin transferred back to cytoplasm to be recycled.
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8
Q

When monomeric GTP binding proteins are bound to GDP, they are:

A

inactive

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9
Q

When monomeric GTP binding proteins are bound to GTP, they are:

A

active

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10
Q

Guanine nucleotide exchange factors (GEFs):

A
  • activate inactive GTP-binding proteins.
  • releases GDP from inactive GTP-binding proteins, allowing GTP to bind.
    • leads to conformational change - active state
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11
Q

GTPases:

A
  • inactivates active GTP-binding proteins
    • hydrolyzes active GTP-binding proteins
    • converts GTP to GDP
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12
Q

Steps in the transport of peroxisome proteins to the peroxisome from the cytoplasm:

A
  1. peroxisome protein synthesis completed in cytoplasm by free ribosomes.
  2. targeting amino acid sequence on protein binds to signal receptor on peroxisome membrane
  3. protein enters peroxisome
  4. heme added to protein in peroxisome, which prevents it from leaving the peroxisome
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13
Q

Zellweger Syndrome:

A
  • mutated peroxisome signal receptor
    • empty peroxisomes
    • peroxisome proteins remain in cytoplasm
    • lethality
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14
Q

What cellular proteins complete their synthesis after becoming associated with the ER?

A

PEGLSM

  • plasma membrane proteins
  • ER proteins
  • golgi proteins
  • lysosomal proteins
  • secreted proteints
  • membrane lipids
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15
Q

The ER is continuous with:

A

the nuclear envelope

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16
Q

Smooth ER is significant in:

A
  • steroid synthesizing cells
  • detoxification in the liver
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17
Q

Steps in the synthesis of proteins that complete their synthesis in the ER:

A
  1. synthesis begins in the cytosol by free ribosomes.
  2. Signal Recognition Particle (SRP) recognizes and binds to N-terminal signal sequence on nascent protein.
  3. Translation temporarily halts.
  4. SRP-bound ribosome attaches to SRP receptor on ER membrane.
  5. Translation begins on ER.
  6. SRP released and recycled.
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18
Q

Signal Recognition Particle (SRP):

A
  • recognizes an N-terminal signal sequence on nascent protein being synthesized by free ribosomes that should be destined for synthesis by the ER.
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19
Q

Protein processing steps in the ER:

A
  1. Signal peptide removed
  2. Hydroxylation of lysine and proline
  3. Disulfide bonds form
  4. Chaperones for folding
  5. Glycosylation and initial steps in oligosaccharide processing
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20
Q

Do improperly folded proteins leave the ER?

A

no; they are sent to the proteasome to be degraded

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21
Q

Steps in glycosylation in ER protein processing:

A
  1. Preformed oligosaccharide with 9 mannoses (high-mannose) is added co-translationally from membrane lipid donor to specific residues, usually Asparagine.
  2. Oligosaccharide is then modified by compartment-specific enzymes
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22
Q

You can tell how far a protein is in being processed by the ER via:

A
  • analyzing the extent of oligosaccharide modifications coming off the protein
    • ER-compartment specific enzymes modify the oligosaccharide one-by-one
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23
Q

Glycosylation and the initial steps in oligosaccharide processing in ER protein synthesis are used for:

A
  • assessing proper folding, which is critical for ER exit!
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24
Q

The ER is the entry-point for:

A

the secretory network

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25
Q

Key advantage of vesicle transport:

A
  • allows transport without passing through membrane
    • hugely energy saving
26
Q

What are the three basic needs for vesicular transport?

A
  1. vesicle formation (need protein coats)
  2. cargo selection
  3. SNAREs allow vesicles to identify target location
27
Q

How is cargo recruited to vesicles?

A
  • by binding to specific receptors that recognize specific signals on the cargo proteins
28
Q

What are the three different protein coats used to deform membrane during vesicle formation?

A
  • clathrin
  • coatamer I (aka COPI)
  • coatamer II (aka COPII)
29
Q

Assembly of COP-I and COP-II (coatamer) coats are regulated by:

A
  • monomeric GTP binding proteins that cycle between active and inactive states
    • ARF for COP-I vesicles
    • Sar-1 for COP-II vesicles
30
Q

What GTP-binding protein regulates the assembly of COP-I vesicles?

A

ARF

31
Q

What GTP-binding protein regulates the assembly of COP-II vesicles?

A

Sar-1

32
Q

Formation of COP-I or COP-II coated vesicles is initiated by:

A
  1. ARF/Sar-1 is activated (GDP → GTP)
    • Fatty acid tail exposed in active state
  2. Activated ARF/Sar-1 fatty acid tail inserts into donor membrane
  3. other COP-I or COP-II subunits bind
33
Q

COP-II coats are used for transport between:

A
  • ER and cis-Golgi
34
Q

COP-I coats are used for transport between:

A
  • Golgi to ER vesicle recycling
  • retrograde and anterograde (maybe) traffic through Golgi
35
Q

Clathrin coats are used for transportation between:

A
  • trans-Golgi network and late endosome
  • cell surface to eary endosome
36
Q

What proteins mediate vesicle-target recognition and fusion?

A
  • v-SNAREs (v = vesicle)
  • t-SNAREs (t = target)
37
Q

Steps in vesicle-target recognition and fusion:

A
  1. v-SNARE on the vesicle recognizes and binds to a t-SNARE on the target.
  2. v-SNARE and t-SNARE form coiled-coil until membranes fuse.
  3. Vesicle contents dumped into target.
38
Q

Botulinum and tetanus toxins cleave:

A

SNAREs

  • Prevent vesicle fusion and neurotransmitter release.
39
Q

What enzymes are involved in checking specificity of vesicle binding?

A

Rab GTPases

40
Q

Summary of vesicle formation and fusion steps:

A
  1. GTP binding protein incorporates into membrane, inner coat forms, SNARE, and cargo recruitment
  2. coat completed with outer layer coat proteins that deform membrane
  3. scission from surface and uncoating to expose SNAREs; recycle coat
  4. tethering may mediate initial attachment, likely recognized in part by Rab
  5. Docking: SNARE interaction (4 helix bundle) occurs, then fusion
41
Q

Materials are transferred from the ER to the Golgi apparatus via vescles coated with:

A

COP-II

42
Q

Proteins that escape the Golgi too early can be retrieved by what sequence and vesicle type?

A
  • KDEL sequence
  • COP-I vesicles
43
Q

What type of vesicle coat brings cargo from the Golgi back to the ER?

A
  • COP-I
44
Q

Golgi Complex Structure:

A
  • 3-8 flattened cisternae that are functionally distinct compartments:
    • cis-face
    • medial
    • trans-face
    • trans-Golgi network
45
Q

The cis-face of the Golgi is oriented toward:

A

the ER

46
Q

The trans-face of the Golgi is oriented toward:

A

secretory granules and lysosomes

47
Q

What major function occurs in the trans-Golgi network?

A

protein sorting and vesicle formation

48
Q

Steps in the shipment of lysosomal enzymes from the Golgi to the late endosome:

A
  1. Mannose residues of lysosomal enzymes are phosphorylated in cis-Golgi; produces a mannose-6-phosphate marker.
  2. Mannose-6-phosphate marker on lysosomal enzymes binds to mannose-6-phosphate receptor (MPR) in the TGN - selectively packaged.
  3. Vesicles form with clathrin coats
  4. Vesicles fuse to late endosome.
  5. Receptor and lysosomal enzymes dissociate in acidic environment of late endosome.
  6. Receptor recycled.
49
Q

How does the TGN recognizes and selectively package lysosomal enzymes only?

A
  • a mannose-6-phosphate marker
    • a mannose residue on the lysosomal enzymes is phosphorylated in the cis-Golgi
50
Q

I-Cell Disease:

A
  • patients lack phosphotransferase; the enzyme that adds a phosphate group to mannose residues in lysosome enzymes.
  • lysosomal enzymes are not recognized by the TGN, and are instead secreted.
51
Q

Constitutively secreted proteins:

A
  • Proteins continuously secreted from cell.
  • Generally by a default pathway that requires no additional information.
    • Examples:
      • immunoglobulin from plasma cells
      • albumin from hepatocytes.
52
Q

Regulated secretory proteins:

A
  • stored in cell and released with appropriate signal.
    • can be stored for a long time.
  • mechanism for targeting remains poorly understood.
  • contents concentrated up to 200-fold during transit.
53
Q

Legionnaire’s Disease:

A
  • bacterium brought into cell via phagocytosis
  • phagosome is not delivered to lysosome as it normally is
  • phagosome becomes ER-like, hijacks host vesicles, and allows them to bind to it
  • bacteria proliferates
54
Q

Endocytosis:

A
  • vesicles pinch off from the plasma membrane and are delivered to specific destinations in the cell following sorting in early endosome.
55
Q

What is the major organelle for sorting endocytosed material?

A
  • early endosome
56
Q

Early endosome pH:

A
  • slightly lower (6-6.5) than that of the cytoplasm and the extracellular environment.
  • causes ligands internalized by receptor mediated endocytosis to dissociate from the receptor.
57
Q

What are the three major destinations of early endosome contents?

A
  1. Receptors recycled to plasma membrane.
  2. Contents form new vesicle and go to another membrane surface: transcytosis.
  3. Contents form late endosomes, which is the route to lysosomes.
58
Q

How are antibodies delivered from the mother to a neonate?

A

transcytosis

59
Q

Process of LDL endocytosis:

A
  1. LDL binds to LDL-receptor on cell.
  2. LDL endocytosed via formation of a vesicle with a clathrin coat.
  3. Vesicles uncoated.
  4. Vesicle with LDL fuses with early endosome.
    • LDL-receptor recycled to surface.
    • LDL delivered to lysosome where it is degraded into free cholesterol and released into the cell.
60
Q

What is one way to regulate extracellular interactions with cell receptors?

A
  • degrade the receptors via endocytosis/lysosome to down regulate their overall activity.
    • e.g. EGFR
61
Q

Adaptin:

A
  • a cytoplasmic protein involved in endocytosis
  • binds to receptor tail, and then clathrin binds to adaptin
62
Q

Familial hypercholestolemia:

A
  • genetic disease: individuals have high serum cholesterol.
  • mutated LDL receptor tail causes failure of adaptin binding, so endocytosis of the LDL/LDL-receptor cannot occur.
    • LDL remains in the blood.

BMS2.16 Vesicle Trafficking (1 decks)

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