Endomembrane System - ER to Golgi

Question 1

2 fates of nascent protein in ER

Answer 1

retained ER
exit from ER

Question 2

2 fates of nascent proteins that remain in ER

Answer 2

stay localized in RER
move laterally through ER lumen or membrane bilayer to another ER subdomain

Question 3

where do the proteins that exit ER initially go

Answer 3

ER exit sites (ERES)

Question 4

what are ERES

Answer 4

ER subdomain involved in formation of transport vesicles destined for Golgi

Question 5

where are ERES usually located

Answer 5

next to cis face of Golgi complex

Question 6

what else is ERES machinery also responsible for

Answer 6

proper packing of vesicle with correct lumenal and membrane cargo proteins

Question 7

why do vesicles at ERES have distinct morphology

Answer 7

due to layer of soluble coat proteins (COPS)

Question 8

what can be found attached to the cytoplasmic surface of nascent vesicle membrane

Answer 8

COPs

Question 9

2 main functions of COPs

Answer 9

1. mediate membrane curvature and formation of vesicle
2. recognize and concentrate specific cargo components into vesicle

Question 10

3 major classes of coat proteins

Answer 10

COPII
COPI
Clathrin

Question 11

how do COPII coated vesicles move

Answer 11

forward from ERES to Golgi - anterograde transport

Question 12

how do COPI-coated vesicles move

Answer 12

backward from Golgi to ER and backward within Golgi - retrograde transport

Question 13

how do clathrin -coated vesicles move

Answer 13

from Golgi to endosomes or from plasma membrane to endosomes

Question 14

what is Sar1

Answer 14

soluble COPII component - a GTPase

Question 15

what is Sec12

Answer 15

an ER intergral membrane protein

Question 16

how does Sec12 function

Answer 16

as a GEF that catalyzes exchange of GDP for GTP on Sar1

Question 17

what are Sec23 and Sec24

Answer 17

soluble proteins form ternary complex with Sar1 at ERES membrane surface

Question 18

where are membrane cargo proteins destined for

Answer 18

exit to ERES for Golgi

Question 19

what do membrane cargo receptor proteins do

Answer 19

bind to soluble lumenal cargo proteins destined to exit ERES for Golgi

Question 20

what are membrane trafficking proteins required for

Answer 20

subsequent trafficking and docking nascent vesicle with proper acceptor membrane

Question 21

what is the most common ER export sorting signal

Answer 21

di-acidic ER export signal (-Asp-X-Glu)

Question 22

where is the ER export sorting signal located

Answer 22

cytoplasmic-facing-domains of Sec24 selected vesicle membrane proteins

Question 23

are ER export signals found on ER resident proteins

Answer 23

NO

Question 24

Sec13 and Sec 31

Answer 24

self assemble to outer cage-like lattice of growing COPII vesicle to act as structural outer scaffolding for growing COPII vesicle bud

Question 25

what does the nascent ERES-derived vesicle contain

Answer 25

soluble and membrane protein cargo molecular machinery

Question 26

where does the vesicle traffic to from ERES

Answer 26

cis-golgi networks

Question 26

how does the cis-golgi network (CGN) get formed

Answer 26

incoming nascent vesicle fuse with one another to form CGN

Question 27

what does the CGN consist of

Answer 27

interconnected network of vesicles and tubules located on cis face of Golgi complex

Question 28

what is the CGN often immediately adjacent to

Answer 28

ERES

Question 29

what does movement of vesicles through cytoplasm get mediated by

Answer 29

cytoskeleton highways molecular motors

Question 30

what are Rab proteins

Answer 30

large family of lipid-membrane anchored, GTP binding proteins associated with all transport vesicles

Question 31

what are Rab proteins key for

Answer 31

regulating vesicle trafficking and fusion

Question 32

what are Rab effector proteins

Answer 32

proteins located on a target membrane that include cytoskeleton motor proteins and bind to activated Rab

Question 33

molecular bridge

Answer 33

when unique vesicle Rabs associate with Rab effectors on specific target membranes

Question 34

what does the binding of Rab and Rab effector convey

Answer 34

vesicle targeting specificity and docking

Question 35

what are SNARE proteins

Answer 35

large family of integral membrane bound proteins located on all transport vesicles AND all target membranes

Question 36

what do SNARES do

Answer 36

mediate provide vesicle targeting specificity fusion of vesicle to target membrane

Question 37

what are the 2 main classes of SNARE proteins

Answer 37

v-SNAREs t-SNARES

Question 38

where are v-SNARES found

Answer 38

transport vesicle membranes

Question 39

where are t-SNARES found

Answer 39

target (acceptor) membranes

Question 40

where are v-SNARES incorporated into

Answer 40

vesicle membrane at site of budding on donor membrane compartment

Question 41

what do all SNARE proteins possess

Answer 41

SNARE-motif

Question 42

what is the SNARE motif

Answer 42

cytoplasmic-facing, coiled coil domain that extend from vesicle/target membrane surface

Question 43

what are NSF and SNAP

Answer 43

cytosolic (soluble) proteins that bind SNARE complexes and unwind SNARE domains linking v/t-SNAREs

Question 44

how do NSF and SNAP unwind SNARE domains

Answer 44

ATP hydrolysis

Question 45

what are the fates of soluble and membrane cargo proteins from ER

Answer 45

either remain in CGN or move to other compartments in endomembrane system

Question 46

what happens to most ER resident proteins

Answer 46

they are retained in ER by exclusions from budding COPII transport vesicles at ERES

Question 47

what happens to escaped ER resident proteins

Answer 47

they are returned from CGN back to ER (retrograde transport) by specific ER retrieval sorting signals

Question 48

what do most resident soluble ER proteins possess

Answer 48

C-terminal -KDEL sequence

Question 49

what does the C-terminal -KDEL sequence serve as

Answer 49

ER retrieval sorting signal

Question 50

what is the KDEL receptor

Answer 50

integral transmembrane protein - lumenal-facing domain binds to KDEL sequence of escaped ER proteins

Question 51

what does COPI protein coat recognize

Answer 51

cytoplasmic-facing domain of KDEL receptor -KKxx sequence

Question 52

why can KDEL receptor return to CGN via COPII-coated ERES vesicles

Answer 52

KDEL receptor has di-acidic ER export sorting signal that is recognized by Sec24

Question 53

what do most resident ER membrane proteins possess

Answer 53

cytoplasmic facing, C-terminal dilysine (-KKxx) sequence

Question 54

why does -KKxx sequence serve as

Answer 54

ER retrieval sorting signal