Unit 4: Golgi Flashcards
What is the structure of the Golgi?
- smooth flattened
- disk like membrane bound cisternae
- <8 cisternae/stack
- specific polarity/orientation
- – cis Golgi network (CGN); cis cisternae; medial cisternae; trans cisternae; trans Golgi network (TGN)
- cisternae are biochemically unique
- supported by protein-based scaffold
How many golgi complex(es) do mammalian cells have in comparison to plant/yeast?
- one large in mammalian
- numerous in plant
Organization of the Golgi complex (stack) is mediated by _______
the Golgi matrix
What is the Golgi Matrix comprised of?
- various golgi peripheral and integral membrane proteins
- cytosolic facing domains interact to form scaffold to link cgn with cisternae and tgn
Example of proteins that aid the formation of the golgicatrix
GRASPS
golgi reassembly and stacking proteins
- tethering proteins to link different golgi subcompartments together
- depletion of GRASP55/65 results in disassembly of golgi complex
What else do golgi matrix proteins link the golgi to? Why is this important?
- links the golgi complex to the cytoskeleton
- positioning and mvt of the golgi is therefore controlled by interaction with cytoskeleton
What is the name of the protein that tethers the Golgi complex to the cytoskeleton?
golgins
Golgi stacks have a distinct polarity both ___ and ___
structurally and functionally
similarities of the cis golgi network and trans golgi network?
- both consist of interconnected network of tubules and vesicles
- both serve a sorting station
What is the role of the cis Golgi network?
sorting station
- destination of COPII vesicles coming from ERES
- site of COPI vesicle assembly for retrograde
- or anterograde transport as CGN matures to rest of golgi complex
Golgi cisternae
- 3 or more flattened cisternae (make up the majority of the organelle
3 sections of the golgi cisternae
- cis
- medial
- trans cisternae
What is the function of the golgi cisternae?
- site where golgi metabolism occurs
- synthesis of polysaccharides
- modification (glycosylation) of proteins/lipids
What does the trans golgi network do? (sites of assembly for 3 things)
- sorting station
- anterograde transport of materials from golgi to other compartments
1. site of clathrin vesicle assembly
2. site for secretory/granule assembly
3. site of COP1 vesicle assembly
Clathrin vesicle assembly at trans goes to where?
- transport to endosome or lysosome (biosynthetic pathway)
Secretory vesicle/granular assembly at trans goes to where?
to plasma membrane (extracellular space)
COP1 vesicle assembly at trans goes to where?
retrograde
back to the trans cisternae
What is the processing plant of the cell?
Golgi complex
What are the 3 functions of the golgi complex?
- synthesis of polysaccharides (EM and cell wall)
- modification of proteins and lipids (glycosylation and proteolytic modification)
- transport and sorting of proteins (at CGN or TGN) via anterograde or retrograde b/w ER Golgi PM
Most glycoproteins (synthesized and N-linked glycosylated in RER) in the golgi are …
subjected to additional glycosylation reactions
How are the cisternaes unique?
the cis medial and trans cisternae have unique glycosyltransferases that modify the glycoprotein specifically
Where is N-linked glycosylation completed?
in the golgi’s cis golgi cisternae
What does N-linked glycosylation involve in the cis golgi cisternae?
- mannosidase 1
- removes 3 mannose sugars from core
How is a lysosomal protein modified when it arrives in the cis golgi cisternae?
- cis golgi cisternae - 2 mannose phosphorylated (signal patch of protein recognized by phosphotransferase)
- Nacetylglucosamine1-phosphate transferred to specific mannose residue from nucleotide sugar donor
How is a lysosomal protein modified when it arrives in the medial golgi cisternae?
- Nacetylglucosamine removed by glycosidase
- lysosomal enzyme contains mannose 6 phosphate group
How is a lysosomal protein modified when it arrives in the TGN?
- recognized by mannose 6 phosphate receptors (MPR)
- targeted to lysosome
What happens to a cargo protein does not have a M6P?
- when it is in the TGN it will go to transport vesicles or granules
- destined for plasma membrane via secretory pathway
Where does N-linked oligosacchardies synthesis occur?
- synthesis begins in ER
- linked by nitrogen
Where does O-linked oligosaccharides synthesis occur?
- entirely in golgi (synthesis and modification)
- linked with oxygen
What a.a. is attached to N-linked oligosacc?
asparagine (N)
What a.a. is attached to O-linked oligosacc?
serines or threonine
What are two models for movement of materials through golgi complex?
- vesicular transport model
- cisternal progression/maturation model
How is cargo carried in the anterograde direction in the vesicular transport model?
- transport vesicles
- subcompartment composition changes with incoming new membrane and cargo
How does the golgi persists in the vesicular transport model?
- COP1 vesicles move resident golgi proteins back to proper subcompartment
- since subcompartments are changing with incoming new vesicles
How do materials move in the cisternal progression/maturation model?
- golgi subcompartments are dynamic structures
- each subcompartment continually moves from cis to trans
How does the composition of each subcompartment change in the cisternal progression model?
- moving through stack, CGN matures to cis cisternae, matures to medial cisternae
- constant change in chemical composition
- vs the VTC the vesicles are just adding/fusing to the subcompartments
How does the golgi persist in the cisternal progression model?
- transport of COP1 vesicles from tips move resident proteins back to proper subcompartments
In the cisternal progression model, how is the new CGN formed?
COPII coated transport vesicles from ERES carry newly synthesized cargo
- they fuse together to form the new CGN
A mannosidase 1 in the trans medial cisternae would go where?
- backwards via COP1 coated vesicle to the cis medial cisternae
- this is where N-linked glycosylation occurs and where it functions
What happens to the TGN in the cisternal progression model?
- TGN disperses into various vesicles
Name 3 types of vesicles from the TGN
- clathrin coated (lysosome/endosome)
- secretory vesicles (transport cargo to PM and extracellular space)
- secretory granules (fuse with PM to release cargo into extracellular space)
