Protein folding Flashcards
endoplasmic reticulum features
continuous with outer membrane
tubules which extend through cytoplasm
2 types of ER
smooth - lipid synthesis
rough - protein synthesis
RER function
synthesis of 2 types of protein - transmembrane and secretion proteins
how are proteins transported into er
co translational translocation
why is there no chaperone protein in co translational translocation
one end of the protein attached to ribosome while other inserts into er (remains in primary sequence)
role of chaperone proteins
bind and escort proteins to mitochondria to prevent damage and folding
signal recognition particle (SRP)
recognises signal sequence on N terminal binding to it and the ribosome (pauses synthesis by binding to pause domain)
purpose of the hinge in SRP
allows binding to protein and ribosome
for co translation translocation the signal sequence must be…
recognised by er and embedded in er membrane
final steps of co translational translocation
once translated, mRNA released back into free ribosome pool
where do proteins go after they are translated
released = fully transported by exocytosis into er lumen
membrane = embedded in er membrane
what happens inside er
modification
glycosylation
glycosylation
adding 14 sugar to N terminus of asparagine side chain of a protein if cannot be folded
importance of glycosylation
quality control, recognition, protection
quality control
- if not folded, 3 glucose and 1 mannose cleaved from N linked oligosaccharide
- if not folded glucosyl transferase enzymes add 1 glucose back (proteostasis)
- calnexin binds to unfolded protein to prevent aggregation
- remove terminal glucose by glucosidase causes release of protein from calnexin
- glucosyl transferase determine if folded right and if not repeats
calnexin
er membrane bound cho binding chaperone protein
purpose of single glucose addition
message to calnexin
if a protein remains misfolded …
it will be released from er and targeted for degradation
what happens if misfolded proteins accumulate
causes er stress and trigger unfolded protein response (UPR)
UPR
inhibits protein synthesis
degrade misfolded proteins
increase transcription of chaperones
role of PERK and IRE1 and ATF6 in UPR
PERK = pauses translation
IRE1 and ATF6 = degradation and activation of genes to increase folding capacity
3 types of vesicle
COPII coated vesicle (from er) EXOCYTOSIS
COPI coated vesicle (from Golgi) ENDOCYTOSIS
Cathrin coated vesicle (from plasma membrane and between Golgi and endosomes)
importance of vesicle coating
ensure specificity and find right membrane
role of GTP and GDP in vesicles
GTP bound = active
GDP bound = inactive
process of release of vesicles
GEF on membrane activate Rab GTP
Rab GTP bind to Rab effector protein on target membrane
causes tethering of vesicles to target membrane
what proteins are involved in membrane fusion
V-SNARES (vesicles) and T SNARES (target)
how to V and T SNARES work
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
process of membrane fusion
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
ER - Golgi
multiple vesicles fuse to form vesicular tubular cutters
what’s the purpose of a retrieval pathway
receptors NSAREs or proteins taken up by accident can be returned to ER
what is the Golgi
stack of flattened membrane enclosed compartments called cistemae
unction
function of Golgi
promote correct folding of proteins
prevent unwanted aggregation
act as signals for sorting and targeting correct pathway
Golgi - lysosomes
what’s a lysosome
degradative organelles (digest unwanted material)
contain enzymes to break down macromolecules
only active at 4.5-5 ph
how’s ph of lysosomes maintained
by vacuolar ATPase
endosomes and lysosomes
late endosome contains ingested material
fuses with lysosome forming endolysosome
once digestion completes lysosomes form
purpose of lysosomes having mannose 6 phosphate tag
direct protein to lysosomal network
endocytosis
transport into cell from plasma membrane
what happens to ingested material once endocytic vesicle fuses with early endosome
degraded using hydrolyses
recycled
2 types of exocytotic pathways
released all at once
selective (maintained din vesicle until needed)
