Protein folding

Question 1

endoplasmic reticulum features

Answer 1

continuous with outer membrane
tubules which extend through cytoplasm

Question 2

2 types of ER

Answer 2

smooth - lipid synthesis
rough - protein synthesis

Question 3

RER function

Answer 3

synthesis of 2 types of protein - transmembrane and secretion proteins

Question 4

how are proteins transported into er

Answer 4

co translational translocation

Question 5

why is there no chaperone protein in co translational translocation

Answer 5

one end of the protein attached to ribosome while other inserts into er (remains in primary sequence)

Question 6

role of chaperone proteins

Answer 6

bind and escort proteins to mitochondria to prevent damage and folding

Question 7

signal recognition particle (SRP)

Answer 7

recognises signal sequence on N terminal binding to it and the ribosome (pauses synthesis by binding to pause domain)

Question 8

purpose of the hinge in SRP

Answer 8

allows binding to protein and ribosome

Question 9

for co translation translocation the signal sequence must be…

Answer 9

recognised by er and embedded in er membrane

Question 10

final steps of co translational translocation

Answer 10

once translated, mRNA released back into free ribosome pool

Question 11

where do proteins go after they are translated

Answer 11

released = fully transported by exocytosis into er lumen
membrane = embedded in er membrane

Question 12

what happens inside er

Answer 12

modification
glycosylation

Question 13

glycosylation

Answer 13

adding 14 sugar to N terminus of asparagine side chain of a protein if cannot be folded

Question 14

importance of glycosylation

Answer 14

quality control, recognition, protection

Question 15

quality control

Answer 15

1. if not folded, 3 glucose and 1 mannose cleaved from N linked oligosaccharide
2. if not folded glucosyl transferase enzymes add 1 glucose back (proteostasis)
3. calnexin binds to unfolded protein to prevent aggregation
4. remove terminal glucose by glucosidase causes release of protein from calnexin
5. glucosyl transferase determine if folded right and if not repeats

Question 16

calnexin

Answer 16

er membrane bound cho binding chaperone protein

Question 17

purpose of single glucose addition

Answer 17

message to calnexin

Question 18

if a protein remains misfolded …

Answer 18

it will be released from er and targeted for degradation

Question 19

what happens if misfolded proteins accumulate

Answer 19

causes er stress and trigger unfolded protein response (UPR)

Question 20

UPR

Answer 20

inhibits protein synthesis
degrade misfolded proteins
increase transcription of chaperones

Question 21

role of PERK and IRE1 and ATF6 in UPR

Answer 21

PERK = pauses translation
IRE1 and ATF6 = degradation and activation of genes to increase folding capacity

Question 22

3 types of vesicle

Answer 22

COPII coated vesicle (from er) EXOCYTOSIS
COPI coated vesicle (from Golgi) ENDOCYTOSIS
Cathrin coated vesicle (from plasma membrane and between Golgi and endosomes)

Question 23

importance of vesicle coating

Answer 23

ensure specificity and find right membrane

Question 24

role of GTP and GDP in vesicles

Answer 24

GTP bound = active
GDP bound = inactive

Question 25

process of release of vesicles

Answer 25

GEF on membrane activate Rab GTP
Rab GTP bind to Rab effector protein on target membrane
causes tethering of vesicles to target membrane

Question 26

what proteins are involved in membrane fusion

Answer 26

V-SNARES (vesicles) and T SNARES (target)

Question 27

how to V and T SNARES work

Answer 27

specific to each other and wrap around each other to form a stable trans SNARE complex which bring the vesicle and membrane within 1.5nm

Question 28

process of membrane fusion

Answer 28

Rab GAP causes Rab to hydrolyse GTP to GDP
Rab GDP released from vesicle and bound by Rab GTP dissociation inhibitor to keep Ra inactive

Question 29

ER - Golgi

Answer 29

multiple vesicles fuse to form vesicular tubular cutters

Question 30

what’s the purpose of a retrieval pathway

Answer 30

receptors NSAREs or proteins taken up by accident can be returned to ER

Question 31

what is the Golgi

Answer 31

stack of flattened membrane enclosed compartments called cistemae

Question 32

unction

Question 33

function of Golgi

Answer 33

promote correct folding of proteins
prevent unwanted aggregation
act as signals for sorting and targeting correct pathway

Question 34

Golgi - lysosomes

Question 35

what’s a lysosome

Answer 35

degradative organelles (digest unwanted material)
contain enzymes to break down macromolecules
only active at 4.5-5 ph

Question 36

how’s ph of lysosomes maintained

Answer 36

by vacuolar ATPase

Question 37

endosomes and lysosomes

Answer 37

late endosome contains ingested material
fuses with lysosome forming endolysosome
once digestion completes lysosomes form

Question 38

purpose of lysosomes having mannose 6 phosphate tag

Answer 38

direct protein to lysosomal network

Question 39

endocytosis

Answer 39

transport into cell from plasma membrane

Question 40

what happens to ingested material once endocytic vesicle fuses with early endosome

Answer 40

degraded using hydrolyses
recycled

Question 41

2 types of exocytotic pathways

Answer 41

released all at once
selective (maintained din vesicle until needed)