31 – Morphology & Function of Golgi Flashcards
Morphology of Golgi
series of flattened disk-shaped membrane cisternae stacked together
Discovery of Golgi
Camillo Golgi - cell body of Purkinje cell that controls our movement
-Illustration of Internal reticular apparatus
Existence of Golgi confirmed by electron microscopy
-Common feature = vesicular tubular structure around Golgi
Golgi cisternae
organized in polarized fashion
-Cis – face ER
-medial - in middle
-Trans – away from ER
–Mature
CGN
cis-golgi network
vesicle + tubules from ER = CGN
Between ER & cis Golgi
TGN
trans-golgi network
vesicles + tubules from trans Golgi = TGN
2 functions of Golgi
- Protein packaging & sorting
- Protein modification when passing through Golgi
Protein packaging & sorting
Proteins made in ER enter Golgi via CGN
-Pass through Golgi & will be concentrated & sorted at TGN
ER resident proteins are often passively transported to Golgi
-Need to retrieve it back to ER
Protein modification when passing through Golgi
N linked oligosaccharides modified
-Started from ER
Proteins might be modified directly
-Cleavage of protein precursors
Sulfation of some tyrosine residues
Protein transport in ER-Golgi interface:
Protein transport from ER to CGN Mediated by …
COPII vesicles
Protein transport from ER to CGN
step by step
- Cargo protein selectively & actively packaged into COPII vesicle
-By di-acidic sorting signals on membrane receptors (Asp-x-Glu (DxE)) - once COPII vesicle bud off from ER
- Coat protein lost: naked vesicle = V-T SNARE pair form = vesicle fuse with CGN
-V SNARE on vesicle
-T SNARE on membrane
-Cargo delivered to CGN
Escaped ER proteins retrieval from CGN, mediated by…
Escaped ER proteins retrieved back to ER by COPI vesicle
Escaped ER proteins retrieval from CGN: step by step:
- BiP (escaped ER proteins) in vesicle
-Chaperone protein in ER to fold protein
-Need to control because might lose all of them
-Can be passively packaged into vesicle & Golgi - once Coat protein COP I vesicle bud off from cis-golgi = become naked vesicle
- V-T SNARE pair between COPI vesicle & ER = retrieved back to ER
signals in retrieval of ER proteins from Golgi
KDEL & KKxx
KDEL receptor (membrane receptor)
KDEL peptide in CGN
Sorting signal -KKxx on C-terminal of missorted (passively) ER-resident protein (BiP/PDI)
-dilysine signal in C-terminal can be recognized by COP I vesicle
KDEL receptor on ER as well = release missorted ER-resident proteins
…controls dissociation & interaction of KDEL peptide & receptor
pH level
Higher (neutral) pH = peptide release
Lower pH = peptide binding
protein transport within Golgi: 2 models
Vesicle transport vs. cisternal maturation (cis to trans)
Protein transport within Golgi (cis to trans)
Vesicle transportation model:
-A population of COPI also moves forward
-Cis Golgi fixed in place
-Transportation of protein from 1 cisternal to next requires vesicle
-Doesn’t explain all protein transportation
Protein transport within Golgi (cis to trans):
cisternal maturation model:
Protein transport through Golgi by cisternal maturation = Without leaving lumen of cisternae
A lot of proteins larger than cargo vesicles = vesicle transportation can’t explain ALL protein transportation
Cisternal maturation can explain
cisternal maturation step by step
- COP II vesicles carrying cargoes bud off from ER fuse one another & become CGN & cis-Golgi
-Tans-Golgi network fusion of vesicle from ER - Newly formed cis-Golgi moves & mature into medial to trans-Golgi to TGN
-Cargoes don’t leave cisternae - When cis-Golgi mature into medial Golgi
-Newly cis-Golgi will form just behind it
- - At TGN, cisternae eventually fragmented into different vesicles – then replaced by another TGN matured right behind it
a. Late endosome & lysosome from TGN - COPI vesicle responsible for retrograde Golgi transport carrying resident Golgi enzymes/proteins back to earlier Golgi cisterna
-Role in maturation
-COPI vesicles retrieve TGN to medial Golgi back
-Depends on protein/cell type - different transport ways
difference between Vesicle transport vs. cisternal maturation
cisternal maturation :
-golgi formed at different time
-its dynamic
-Not fixed in place
Golgi maturation visualized in live yeast cells
Proof of maturation
-No proof of observation in living organisms because its stacked
-Can see how cis-Golgi transition to trans-Golgi
