Lecture 10 - endomembrane system part 5 golgi

Question 1

What is the general structure of the golgi?

Answer 1

complex or stack of flattened membrane bound cisternae with dilated edges and numerous associated tubules and vesicles

Question 1

What is the difference in the golgi for mammalian vs plant cells?

Answer 1

mammalina - one large golgi complex located near center of cell

plant - several golgi complexes located throughout the cell

Question 2

Where is the CGN located?

Answer 2

cis face of the golgi complex

Question 3

What does the CGN consist of?

Answer 3

complex, interconnected network of tubules and vesicles adjacent to ERES

Question 4

What are the four functions of the CGN?

Answer 4

1. destination of COPII vesicles coming forward (anterograde) from ERES to CGN
2. site of COPI vesicle assembly for transport back (retrograde) from CGN to ER
3. forward transport as CGN matures into next subcompartment of golgi complex
4. destination of COPI vesicles moving back from next subcompartment of golgi complex to CGN

Question 5

What are the golgi cisternae?

Answer 5

series of three+ large flattened cisternae (comprise majority of golgi structure)
sites of golgi metabolism

Question 6

What are the three main sections of the cisternae?

Answer 6

cis, medial and trans

Question 7

Where is the TGN located?

Answer 7

trans face of golgi complex

Question 8

What is the TGN?

Answer 8

interconnected network of tubules and vesicles

Question 9

What are the four functions of the TGN?

Answer 9

1. forward (anterograde) transport as previous subcompartment of golgi complex matures into TGN
2. site of clathrin coat vesicle assembly for transport forward (anterograde) from TGN to endosomes
3. site of secretory vesicle and secretory granule assembly for transport forward (anterograde) to pm
4. site of COPI vesicle assembly for transport back (retrograde) to golgi trans cisternae

Question 10

What is the organization of the golgi complex mediated by?

Answer 10

golgi matrix

Question 11

What is the golgi matrix?

Answer 11

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

Question 12

What are GRASPs?

Answer 12

tethering proteins to link different golgi subcompartments together

Question 13

How does glycosylation end in the golgi?

Answer 13

most glycoproteins moving through golgi are subjected to additional glycosylation reactions

Question 14

How does glycosylation occur in the golgi in an assembly line?

Answer 14

act as an assembly line
core oligosaccharides on proteins moving through golgi modified sequentially by different enzymes in each subcompartment

Question 15

What do cis medial and trans golgi cisternae possess for glycosylation?

Answer 15

glycosyltransferase and glycosidase enzymes

Question 16

How does alpha-mannosidase I in the golgi glycosylate the proteins?

Answer 16

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

Question 17

How are sorting signals for lysosomes formed in the golgi?

Answer 17

other modifications to oligosaccharide core of glycoprotein in golgi

Question 18

How are M6P sorting signals formed?

Answer 18

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

Question 19

What do M6P groups serve as in the golgi?

Answer 19

signal patch for soluble lysosomal protein targeting

Question 20

Where proteins that don’t have M6P packaged at TGN go?

Answer 20

into secretory transport vesicles/granules destined for pm

Question 21

What happens to proteins with M6P packaged at TGN?

Answer 21

into clathrin-coated transport vesicle to endosomes and then lysosomes

Question 22

How do proteins move through golgi complex?

Answer 22

cisternal progression/maturation model

Question 23

What is the cisternal progression/maturation model?

Answer 23

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’

Question 24

What are the subcompartments movement and progression mediated by?

Answer 24

golgi matrix proteins and cytoskeleton motors

Question 25

What forms the new CGN?

Answer 25

incoming vesicles fuse together

Question 26

What is the order of the golgi maturation?

Answer 26

CGN -> cis cisternae -> medial cisternae -> trans cisternae -> TGN

Question 27

What type of vesicle transports resident golgi enzymes backwards through the complex?

Answer 27

COPI

Question 28

What happens to the TGN in the maturation model?

Answer 28

eventually disperses into various types of transport vesicles, which deliver certain cargo proteins from TGN to different compartments in endomembrane

Question 29

What are some of the transporters that form from the maturing TGN?

Answer 29

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