3.4 - ER-Golgi

Question 1

whats carried in transport vesicles from Golgi?

Answer 1

membrane components and soluble proteins

Question 2

ER-exit sites (ERES)

Answer 2

specific points of rER where cargo buds off from

Question 3

what are COPII coated vesicles essential for?

Answer 3

protein export from the ER

Question 4

how are vesicular tubular clusters (VTCs) formed?

Answer 4

COPII vesicles undergo fusion

Question 5

trans-Golgi network (TGN)

Answer 5

term given to exiting cargo from the Golgi

Question 6

components required to make vesicle (3)

Answer 6

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

Question 7

variants of Sar1 protein (2)

Answer 7

1. SAR1A (mammalian name)
2. Sar1 (yeast name)

Question 8

role of Sar1 protein

Answer 8

regulates the assembly and disassembly of COPII coats in membrane trafficking

Question 9

Sar1 protein

Answer 9

monomeric small GTPase found in COPII vesicles

Question 10

what superfamily of proteins is Sar1 a member of?

Answer 10

‘ras superfamily’

Question 11

Sar1 exchange factors (2)

Answer 11

1. Sec12 - GDP -> GTP
2. Sec23/24 (GAP) - GTP -> GDP + Pi

Question 12

Sar1 switches (2)

Answer 12

1. GTP = ‘on’
2. GDP = ‘off’

Question 13

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

Answer 13

interacts with membrane-bound exchange factor Sec12

Question 14

role of sec 13/31 exchange factor (2)

Answer 14

1. completes COPII coat of vesicle
2. bends membrane and releases vesicle

Question 15

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

Answer 15

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

Question 16

role of Sec12 in COPII vesicle formation

Answer 16

exchanges GDP for GTP bound to Sar1 through its GEF activity

Question 17

Rab superfamily

Answer 17

another branch of ras superfamily

Question 18

rab protein role

Answer 18

GTP binding/ hydrolysis (cycle on and off membrane)

Question 19

how may rab proteins are involved per stage of trafficking?

Answer 19

~1

Question 20

rab protein function

Answer 20

lipid ‘anchor’ in membrane

Question 21

retrograde traffic

Answer 21

vesicle transport from golgi to ER (COPI coated vesicles)

Question 22

anterograde traffic

Answer 22

vesicle transport from ER to golgi (COPII coated vesicles)

Question 23

COPI vesicle formation initiation

Answer 23

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

Question 24

where are the GEF Gea1/Gea2 proteins located?

Answer 24

peripherally located in Golgi membrane

Question 25

what does the heptamer complex of the COPI coat associate with when recruited? (2)

Answer 25

1. cargo 2. 2 Arf1 molecules through inner layer coat complex

Question 26

modification that takes place in Golgi

Answer 26

glycosylation

Question 27

what does the golgi sort? (3)

Answer 27

1. plasma membrane 2. lysosomes 3. back to ER

Question 28

glycosylation in the golgi

Answer 28

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

Question 29

glycosidases

Answer 29

removes sugars

Question 30

glycosyl transferase

Answer 30

adds sugars

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

enter constitutive secretory pathway

Question 34

why is ER retention required

Answer 34

some ER proteins are soluble but stay in the ER (e.g. chaperones)

Question 35

ER retention signal

Answer 35

C-terminal tag (usually KDEL)

Question 36

KDEL retention signal role

Answer 36

if KDEL protein escapes receptor binds in golgi and returns it to ER