Exocytosis (Unit 4 post-Test 2)

Question 1

How does Exocytosis work in polarized cells?

Answer 1

Direct or Indirect Pathways

Direct Pathway:
-Separated at TGN
-GSL and Cholesterol self-associate into lipid rafts to be carried to the apical side
-Any GPI-anchored proteins will also associate with GSL

Indirect (Transcytosis)
-Endocytose proteins that went to wrong membrane
-Place in early endosome which will take it to the right membrane

Question 1

Why do we have secretory vesicles?

Answer 1

Concentrate and store substrates so we can let them out in large amounts when prompted

Question 2

Why would we want to enlargen the PM?

Answer 2

-Repair
-Make more cells
-Phagocytosis
-Cytokinesis

Question 3

How does exocytosis repair the PM?

Answer 3

Local membranes like lysosomes donate to form temporary patch (along with homotypic vesicle fusion)

This reduces bilayer tension and allows it to flow so that it can reseal itself

*patch is temporary bc it doesn’t have the normal components a PM should have

Question 4

What kind of secretory vesicles do nerve cells have?

Answer 4

Synaptic vesicles and the normal ones

Question 5

How are synaptic vesicles formed?

Answer 5

Membrane components brought to pre-synaptic membrane OR Endocytose old synaptic vesicle membrane for direct formation
OR
to give it to endosome which will then bud off to form vesicle

Load up the neuro transmitter

Question 6

What are good markers for synaptic vesicles?

Answer 6

SNAREs
Rabs
Metabolitte transporters
V-ATPases

Question 7

What are the steps for synaptic vesicle endocytosis?

Answer 7

Docking: Synaptobrevin (v-SNARE) on the vesicle mixes with SNAP 25 and syntaxin (t-SNAREs) on membrane

Priming 1: Partial assembly of SNARE bundle
Priming 2: complexin is added to freeze SNARE in a metastable state

Ca2+ (or other trigger that results in Ca2+) activates synaptotagmin which releases complexin thus opening the fusion pore

Fusion is complete!

Question 8

What are synaptic vesicles?

Answer 8

Neurotransmitter carriers that fuse quickly
Only a small # is docked at a time but they allow rapid fire of nerves

Question 9

If I put engineer a secretory protein to be expressed in a cell that doesn’t normally secrete it what will happen?

Answer 9

It will be secreted bc all secretory proteins use the same vesicle packing method (we think!)

Question 10

How are synaptic vesicle cargo proteins typically made?

Why?

Answer 10

As pre-pro proteins
Pre-peptide cleaved in ER
Pro-peptide cleaved during vesicle maturation by cell-specific proteases

Done bc small molecules can be dangerous to the cell