Lecture 10 - endomembrane system part 5 golgi Flashcards
What is the general structure of the golgi?
complex or stack of flattened membrane bound cisternae with dilated edges and numerous associated tubules and vesicles
What is the difference in the golgi for mammalian vs plant cells?
mammalina - one large golgi complex located near center of cell
plant - several golgi complexes located throughout the cell
Where is the CGN located?
cis face of the golgi complex
What does the CGN consist of?
complex, interconnected network of tubules and vesicles adjacent to ERES
What are the four functions of the CGN?
- destination of COPII vesicles coming forward (anterograde) from ERES to CGN
- site of COPI vesicle assembly for transport back (retrograde) from CGN to ER
- forward transport as CGN matures into next subcompartment of golgi complex
- destination of COPI vesicles moving back from next subcompartment of golgi complex to CGN
What are the golgi cisternae?
series of three+ large flattened cisternae (comprise majority of golgi structure)
sites of golgi metabolism
What are the three main sections of the cisternae?
cis, medial and trans
Where is the TGN located?
trans face of golgi complex
What is the TGN?
interconnected network of tubules and vesicles
What are the four functions of the TGN?
- forward (anterograde) transport as previous subcompartment of golgi complex matures into TGN
- site of clathrin coat vesicle assembly for transport forward (anterograde) from TGN to endosomes
- site of secretory vesicle and secretory granule assembly for transport forward (anterograde) to pm
- site of COPI vesicle assembly for transport back (retrograde) to golgi trans cisternae
What is the organization of the golgi complex mediated by?
golgi matrix
What is the golgi matrix?
consists of various golgi peripheral and intergral membrane proteins, cytoplasmic facing domains interact to form scaffold - link CGN, cis/medial/trans cisternae and TGN together
also links golgi complex to cytoskeleton - positioning and movement of the golgi
What are GRASPs?
tethering proteins to link different golgi subcompartments together
How does glycosylation end in the golgi?
most glycoproteins moving through golgi are subjected to additional glycosylation reactions
How does glycosylation occur in the golgi in an assembly line?
act as an assembly line
core oligosaccharides on proteins moving through golgi modified sequentially by different enzymes in each subcompartment
What do cis medial and trans golgi cisternae possess for glycosylation?
glycosyltransferase and glycosidase enzymes
How does alpha-mannosidase I in the golgi glycosylate the proteins?
in cis cisternae, removes 3 mannose sugars from core oligosaccharide of glycoprotein
glycoprotein moves to medial cisternae and the trans for additional processing reactions
final processed glycoprotein resides in golgi or targets to pm
How are sorting signals for lysosomes formed in the golgi?
other modifications to oligosaccharide core of glycoprotein in golgi
How are M6P sorting signals formed?
is cis cisternae, mannose units in core oligosaccharide of soluble proteins destined for lysosomes are phosphorylated
N-acetyl glucosamine phosphotransferase recognizes unique sequences in lysosomal destined proteins
addition of M6P residues prevents lysosomal destined proteins from being subjected to N-linked glycosylation reactions
What do M6P groups serve as in the golgi?
signal patch for soluble lysosomal protein targeting
Where proteins that don’t have M6P packaged at TGN go?
into secretory transport vesicles/granules destined for pm
What happens to proteins with M6P packaged at TGN?
into clathrin-coated transport vesicle to endosomes and then lysosomes
How do proteins move through golgi complex?
cisternal progression/maturation model
What is the cisternal progression/maturation model?
golgi subcompartments continually move forward from cis to trans side of golgi complex
and the composition of each subcompartment changes while moving cis to trans through the complex
the only reason golgi complex persist is because COPI transport vesicles continually move resident golgi proteins back to proper subcompartment as it ‘ages’
What are the subcompartments movement and progression mediated by?
golgi matrix proteins and cytoskeleton motors
What forms the new CGN?
incoming vesicles fuse together
What is the order of the golgi maturation?
CGN -> cis cisternae -> medial cisternae -> trans cisternae -> TGN
What type of vesicle transports resident golgi enzymes backwards through the complex?
COPI
What happens to the TGN in the maturation model?
eventually disperses into various types of transport vesicles, which deliver certain cargo proteins from TGN to different compartments in endomembrane
What are some of the transporters that form from the maturing TGN?
clathrin-coated vesicles - with M6P bearing protein cargo target to endosomes
secretory vesicles - target to pm
secretory granules - eventually target to pm
COPI-coated vesicles - target to trans golgi cisternae
