Protein Trafficking 3

Question 1

budding from the ER- integral proteins, lumenal cargo proteins

Answer 1

Some proteins selectively recruited into buds eg some integral proteins have cytoplasmic domains that interact with coat proteins- concentrates them into buds
Lumenal cargo proteins can be selectively recruited into buds by interacting with cargo receptors- span ER membrane and interact with coat proteins

Question 2

What proteins might be excluded from entering budding vesicles

Answer 2

proteins that misfold in the ER

Question 3

what happens to proteins passively included in budding vesicle

Answer 3

may need to be returned to ER

Question 4

Antibodies and budding vesicles

Answer 4

excluded from budding vesicles until correctly assembled

BiP keeps protein from leaving ER when not assembled

Question 5

Fully assembled antibody

Answer 5

4 PP chains, 2 light and 2 heavy

Both synthesised on ribosomes and translocated into ER lumen- assemble before the complex leaves ER

Question 6

Some cargoes returned to the ER

Answer 6

retrograde transport

mechanisms in golgi for returning the proteins to the ER

Question 7

What do the protein sent back to the ER from the golgi have

Answer 7

These proteins have the KDEL sequence at their C termini- can be sent back in COPI vesicles

Question 8

How does the retrograde transport work

Answer 8

Proteins recognised by KDEL receptors and concentrated within golgi vesicles.

Question 9

How does the KDEL receptor travel back to the golgi

Answer 9

when in the ER it releases the protein and returns to the golgi in COPII vesicle

Question 10

Targeting vesicles to the correct membrane

Answer 10

Vesicle must find acceptor compartment, fuse and release contents
Rab and SNARE proteins give vesicles and target membranes a molecular identity- only if these are compatible does fusion take place

Question 11

Tethering

Answer 11

Molecular interaction between tether and vesicle, then docking then fusion step with snare protein (see useful diagram)

Question 12

snare pairing

Answer 12

brings 2 membranes closer together and forces them to fuse

The V and T snare coil around each othrer

Question 13

ER protein modification

Answer 13

N-linked glycosylation in ER
Sugars transferred from dolichol (lipid) onto proteins with NXS/T sequences in the lumen of the ER
Occurs on asparagine residues

Question 14

Which enzyme transfers lipid to protein in glycosylation

Answer 14

oligosaccharyl transferase

Question 15

What type of glycosylation in the golgi

Answer 15

O- linked glycosylation

Question 16

chaperones

Answer 16

prevent misfolded/unassembled proteins leaving the ER

Question 17

Golgi faces

Answer 17

cis and trans face
cis receives vesicles from ER and trans packages them
Different parts of the golgi have different enzymes for carrying out different processes

Question 18

2 types of vesicles trans golgi packages into

Answer 18

constitutive or regulated secretory vesicles

Question 19

Regulation secretion controlled by

Answer 19

signal transduction pathways ie only fuse with membrane upon signal

Question 20

constitutive secretion

Answer 20

unregulated membrane fusion

Question 21

Lysosomes - Ph and why and how is it maintained, how are lysosomes related to the golgi

Answer 21

acidic pH with hydrolases
Lumen kept acidic by proton pump, uses ATP
Some protein transported to the golgi via lysosomes

Question 22

Endocytosis (LDL)

Answer 22

LDL receptor trafficked to cell surface from ER
Receptor cycles between plasma mem and endosomes picking up LDL at PM and releasing it in endosomes (acidic pH)
LDL is trafficked to lysosomes, receptor returns to the PM (useful diagram)