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Cell and Molecular Biology > 3.4 - ER-Golgi > Flashcards

3.4 - ER-Golgi Flashcards

1
Q

secretory pathway of Golgi

A

transport vesicles bud from one membrane and fuse with another

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2
Q

whats carried in transport vesicles from Golgi?

A

membrane components and soluble proteins

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3
Q

ER-exit sites (ERES)

A

specific points of rER where cargo buds off from

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4
Q

what are COPII coated vesicles involved in?

A

cargo selection and membrane budding

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5
Q

what are COPII coated vesicles essential for?

A

protein export from the ER

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6
Q

how are vesicular tubular clusters (VTCs) formed?

A

COPII vesicles undergo fusion

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7
Q

trans-Golgi network (TGN)

A

term given to exiting cargo from the Golgi

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8
Q

components required to make vesicle (3)

A
  1. coat (COPII)
  2. switch (Sar1)
  3. ‘sec’ proteins
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9
Q

variants of Sar1 protein (2)

A
  1. SAR1A (mammalian name)
  2. Sar1 (yeast name)
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10
Q

role of Sar1 protein

A

regulates the assembly and disassembly of COPII coats in membrane trafficking

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11
Q

Sar1 proteins

A

monomeric small GTPase found in COPII vesicles

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12
Q

what superfamily of proteins is Sar1 a member of?

A

‘ras superfamily’

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13
Q

Sar1 exchange factor

A

GDP removed -> new GTP bound and GTPase activating protein (GAP)

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14
Q

Sar1 switches (2)

A
  1. GTP = ‘on’
  2. GDP = ‘off’
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15
Q

how does GDP-bound Sar1 exchange its bound GDP for GTP?

A

interacts with membrane-bound exchange factor Sec12

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16
Q

what exchange factors are responsible for completing the COPII coat of vesicles

A

Sec13/31

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17
Q

what happens after the COPII coat of a vesicle is completed

A

bend the membrane and release the vesicle

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18
Q

what happens after a vesicle has been released? (3)

A
  1. Sec23/24 GAP now active
  2. Sar1 hydrolyses GTP and falls off membrane
  3. so does coat
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19
Q

how is membrane deformation initiated? (1st stage vesicle formation)

A

Sec12 catalyses guanine nucleotide exchange on Sar1, recruiting Sar1 to ER membrane

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20
Q

2nd stage vesicle formation

A

Sar1 at membrane recruits inner coat proteins (Sec23-Sec24 heterodimer)

21
Q

pre-budding complex formation (3rd stage vesicle formation)

A

Sec24 subunit binds to cargo proteins that need to be transported out of the ER

22
Q

where are the formation of pre-budding complexes concentrated?

A

ER exit sites (ERES)

23
Q

what happens to soluble cargo in ER lumen (4th stage vesicle formation)

A

can be captured by transport adaptors

24
Q

what happens to pre-budding complexes (5th stage vesicle formation)

A

outer COPII coat (Sec13-Sec31 heterodimer) binds and collects pre-budding complexes

25
Q

how is soluble bulk flow cargo trapped inside a vesicle? (6th stage vesicle formation)

A

full COPII assembly leads to fission of a vesicle from donor ER membrane

26
Q

coat disassembly (7th stage vesicle formation)

A

hydrolysis of GTP bound to Sar1 leads to COPII coat disassembly

27
Q

role of Sec12 in COPII vesicle formation

A

exchanges GDP for GTP bound to Sar1 through its GEF activity

28
Q

Rab superfamily

A

another branch of ras superfamily

29
Q

rab protein role

A

GTP binding/ hydrolysis (cycle on and off membrane)

30
Q

how may rab proteins are involved per stage of trafficking?

31
Q

rab protein function

A

lipid ‘anchor’ in membrane

32
Q

retrograde traffic

A

vesicle transport from golgi to ER (COPI coated vesicles)

33
Q

anterograde traffic

A

vesicle transport from ER to golgi (COPII coated vesicles)

34
Q

another way COPI vesicle formation is initiated

A

GTP-GDP exchange on Arf1 through action of the GEF Gea protein (Gea1/Gea2)

35
Q

where are the GEF Gea1/Gea2 proteins located?

A

peripherally located in Golgi membrane

36
Q

how is the heptamer complex of the COPI coat recruited?

A

en bloc, associating with cargo as well as 2 Arf1 molecules through inner layer coat complex

37
Q

role of the amphipathic helix of Sar1 and Arf1 in COPII

A

some role in scission of budded vesicles

38
Q

when are vesicles formed in COPII

A

upon polymerisation of outer coat

39
Q

modification that takes place in Golgi

A

glycosylation

40
Q

what does the golgi sort? (3)

A
  1. plasma membrane
  2. lysosomes
  3. back to ER
41
Q

golgi appearance under electron microscope

42
Q

glycosylation in the golgi

A

core N-linked oligosaccharides pruned and modified both in ER and golgi by specific glycosidases and glycosl transferases

43
Q

glycosidases

A

removes sugars

44
Q

glycosyl transferase

A

adds sugars

45
Q

how are lysosomal proteins modified and packaged in golgi? (2)

A
  1. tagged with mannose-6-phosphate
  2. packaged into specific vesicles for onward trafficking
46
Q

how are secretory proteins (e.g. insulin) packaged in golgi?

A

packaged into secretory vesicles ready for exocytosis where the membrane of vesicle with fuse with cell membrane

47
Q

how are cell surface proteins (e.g. phospholipids and glycoproteins) sorted in the golgi?

A

enter constitutive secretory pathway

48
Q

summary of vesicle formation (5)

A
  1. sorting, budding, targeting and fusion
  2. coats formed from subunits in cytosol
  3. coat falls off
  4. Rab proteins and tethers
  5. SNARE proteins and membrane fusion

Cell and Molecular Biology (20 decks)

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