Class 15 - Exocytosis (GOOD)

Question 1

Exocytosis

Answer 1

Fusion of vesicles with the plasma membrane.

Regulated exocytosis delivers more membrane to enlarge plasma membrane when needed (cytokinesis, cellularization), and makes temporary patches in response to mechanical stress.

Question 2

Constitutive secretory pathway

Answer 2

Exocytosis which operates continually and vesicles come directly from TGN to fuse with plasma membrane.

Question 3

Regulated secretory pathway

Answer 3

Used by specialized secretory cells. Pathway in which proteins from TGN are initially stored in secretory vesicles for later release to plasma membrane by exocytosis.

Question 4

Default pathway

Answer 4

The nonselective constitutive secretory pathway, transporting proteins directly to cell surface.

Does not require a signal.

In unpolarized cells, almost all proteins go on this path unless retained in organelles.

Question 5

Secretory proteins

Answer 5

Any protein secreted by the cell. Reach plasma membrane via the regulated secretory pathway, as secretory vesicles, for which proteins require specific signals to get to.

In TGN, sorted into appropriate vesicles by forming aggregates.

Question 6

Secretory vesicles

Answer 6

Form from the TGN and release contents into cell exterior by exocytosis in response to signals.

As they mature, clathrin-coated transport vesicles bud off and go back to TGN —> more concentrated secretory vesicle

Question 7

Synaptic vesicles

Answer 7

Specialized class of tiny secretory vesicles in nerve cells which contain neurotransmitter molecules.

Fuse with plasma membrane in response to Ca2+ influx

Enter primed state to allow rapid release - SNAREs partly paired but not fully wound.

Recycled from presynaptic membrane, quickly replaced by more primed vesicles.

Question 8

Three pathways of protein sorting from TGN

Answer 8

1. Constitutive secretory pathway (directly to plasma membrane)
2. Regulated secretory pathway (through secretory vesicles released by signals).
3. Endosomes

Question 9

Exocytosis in polarized cells

Answer 9

Apical domain - Faces internal cavity or outside world

Basolateral domain - Covers rest of the cell

Separated by tight junctions

Direct pathway - Sorted at TGN and delivered to correct domain.

Indirect pathway - Delivered from TGN to wrong domain—>endocytosis—>early endosomes—>delivery to correct domain (transcytosis).