11_Sorting at TGN

Question 1

What are the three major functions of the secretory pathway?

Answer 1

1) allows secreted proteins to leave the cell
2) builds and transports integral membrane proteins and lipids, providing components for the membranes of the cell
3) facilitates post-translational modification of proteins and sugar-rich compounds (e.g. glycoproteins)

Question 2

What triggers the binding of the ER-resident protein to its receptor when fused and released into the cis-Golgi?

Answer 2

∆pH to more acidic in the Golgi environment compared to ER

Question 3

What is the amino acid sequence at the C-terminus of ER-resident proteins that serves as their retrieval sequence?

Answer 3

KDEL

Question 4

What is the coating of the vesicles used to return ER-resident proteins to the ER from the cis-Golgi?

Answer 4

COPI

Question 5

Why does low pH result in binding of KDEL to its receptor?

Answer 5

pH probably changes receptor conformation

Question 6

pH (increases/decreases) from the ER to the Golgi.

Answer 6

decreases

Question 7

Endocytosis pathways lead (in/out) while exocytosis pathways lead (in/out).

Answer 7

endo: in
exo: out

Question 8

Are extracellular matrix components secreted constitutively or in a regulated fashion?

Answer 8

constitutive secretion

Question 9

What is material meant to be secreted in a regulated way stored?

Answer 9

membrane-bound compartments

Question 10

What category of enzymes are contained within lysosomes?

Answer 10

acid hydrolases

Question 11

What type of pump maintains low pH in lysosomes?

Answer 11

V-ATPase

Question 12

What is used to tag lysosomal enzymes when sorted at the TGN? Which receptors recognize these tagged enzymes?

Answer 12

phosphorylated mannose residues

recognized by mannose 6-phosphate receptors (MPRs)

Question 13

Mannose 6-phosphate is not directly attached to an lysosomal hydrolase; what is it attached to?

Answer 13

an N-linked oligosaccharide

Question 14

Where is the M6P added to lysosomal hydrolase precursors?

Answer 14

the cis Golgi network

Question 15

What is an example of a regulatory secretory pathway? What is the stimulus for secretion in this pathway?

Answer 15

secretion of glucose receptors is regulated. Normally, the glucose receptors are kept in specialized recycling endosomes. When insulin is bound to its receptor on the cells surface, glucose receptors relocalize to the cell surface to increase uptake of glucose.