Lecture 12 - Endomembranes & Golgi

Question 1

Def: further processes and sorts glycoproteins and membrane lipids, playing a central role in membrane and protein trafficking in eukaryotic cells

Answer 1

Golgi complex

Question 2

What happens in the Golgi complex?

Answer 2

Further glycosylation and processing of carbohydrate side chains occurs

Question 3

Where does terminal glycosylation occur?

Answer 3

In the Golgi apparatus

Question 4

Def: modifications of glycoproteins through the removal/addition of sugars side chains on the core oligosaccharide

Answer 4

Terminal glycosylation

Question 5

All glycosylation reactions occur on the luminal side of the membrane thus contributing to __________ _________

Answer 5

Membrane asymmetry

Question 6

Key point to remember for gycolsylation:

Answer 6

Each step is strictly dependent on the preceding modification

Question 7

what are the functions of glycosylation in the Golgi complex

Answer 7

1. participate in protein/lipid sorting in the TGN
2. makes glycoproteins/membranes more resistant to digestion by proteases, by creating the glycocalyx
3. serve as recognition molecules in cell-cell interaction, and unfortunately viruses also use it for viral entry
4. regulatory roles, ABO blood type, and immune-recognition

Question 8

what is the “bottom line” of Golgi complex glycosylation?

Answer 8

gives the cell ability to generate many chemically distinct molecules at the cell surface

Question 9

what are the 2 models for movement through the Golgi

Answer 9

1. stationary cisternae model
2. cisternal maturation model

Question 10

def: model in which the cisternal and the resident enzymes stay in place, while cargo moves from one stack to the next

Answer 10

stationary cisternae model

Question 11

def: model in which the cargo remains within a cisternae, while the cisternal moves forward (-cis to trans-) and resident enzymes shuttle backwards in vesicles

Answer 11

cisternal maturation model

Question 12

what proteins would be found in the transport vesicles in the stationary cisternae model?

Answer 12

cargo

Question 13

what proteins would be found in the transport vesicles in the cisternal maturation model?

Answer 13

resident enzymes

Question 14

if ER-Golgi transport was inhibited what would happen in the stationary cisternae model?

Answer 14

there would be little change in the Golgi structure

Question 15

if ER-Golgi transport was inhibited what would happen in the cisternal maturation model?

Answer 15

the golgi would dissapear

Question 16

def: movement of material toward the plasma membrane

Answer 16

anterograde transport

Question 17

def: movement of material towards the ER

Answer 17

retrograde transport

Question 18

def: fusion of vesicles with the plasma membrane, releasing their contents into the extracellular space

Answer 18

exocytosis

Question 19

def: formation of a vesicle on the plasma membrane, taking up solutes from the extracellular space

Answer 19

endocytosis

Question 20

sorting of proteins begins in the __, with the final sorting occurring in the ___

Answer 20

ER, TGN

Question 21

what is the most established type of targeting of proteins from the rough ER?

Answer 21

lysosomal targeting

Question 22

what are the two mechanisms that keep proteins within an organelle?

Answer 22

retention and retrieval

Question 23

def: resident molecules are excluded from transport vesicles

Answer 23

retention

Question 24

def: “tags” can be used to return “escaped” proteins to their proper location

Answer 24

retrieval

Question 25

what are the requirements the sorting signals must fulfill?

Answer 25

1. if mutated, sorting is lost
2. if transplanted to an unsorted protein, that protein is now sorted

Question 26

what are 3 examples of tags on proteins?

Answer 26

1. amino acid sequence
2. hydrophobic domain
3. oligosaccharide side chain

Question 27

what is the most common ER retention tag?

Answer 27

the KDEL retrieval signal

Question 28

def: short C-terminal amino acid sequence (Lys-Asp-Glu-Leu) that mediates the return of soluble proteins to the ER

Answer 28

KDEL retrieval signal

Question 29

where are membrane proteins retrieval signals?

Answer 29

on their cytosolic domains

Question 30

what is the most common ER specific transmembrane protein?

Answer 30

KKXX (Lys-Lys-any-any)

Question 31

KDEL proteins are meant to be ____ _______

Answer 31

ER residents

Question 32

what happens if KDEL proteins escape to the ER?

Answer 32

they associate with the KDEL receptor

Question 33

what do KDEL receptors do?

Answer 33

mediate the packaging of KDEL proteins into ER-bound transport vesicles

Question 34

is KDEL to KDEL receptor binding efficient or inefficient in the Golgi?

Answer 34

it is efficient in the lower pH environment of the Golgi

Question 35

is KDEL to KDEL receptor binding efficient or inefficient in the ER?

Answer 35

inefficient due to the higher pH of the environemnt

Question 36

what happens to soluble lysosomal enzymes in the ER and the early compartments of the Golgi

Answer 36

they undergo N-glycosylation followed by removal of glucose and mannose units

Question 37

what ensure the delivery of lysosomal proteins to the lysosomes?

Answer 37

a mannose-6-phosphate tag