Lecture 12: Exocytosis, Endocytosis, and recycling

Question 1

Exocytosis

Answer 1

Transport from the trans golgi network to the cell exterior

Question 2

Constitutive vs regulated secretion

Answer 2

Question 3

What are the three sorting possibilities in the TGN?

Answer 3

1. Signal-mediated diversion to lysosomes via endosomes (mannose-6-phosphate receptors)
2. Signal-mediated diversion to secretory vesicles (for regulated secretion)
3. Constitutive secretory pathway

Question 4

____ help mark organelles and membrane domains in the late secretory pathway

Answer 4

Phosphoinositides

Question 5

Regulated secretory vesicles are also called secretory _____ based on their appearance under the electron microscope

Answer 5

granules or dense-core granules

Question 6

How does proteolytic processing occur in the late Golgi and within secretory vesicles?

Answer 6

Different peptide hormones can be made from the same pre-protein in different cell types

Question 7

What are the 5 stages of synaptic vesicle fusion?

Answer 7

Question 8

Compound exocytosis? example?

Answer 8

Compound exocytosis - vesicle-vesicle fusion as well as vesicle PM fusion

Ex-mast cell degranulation

Question 9

GLUT4 translocation is an example of ____. How does this work?

Answer 9

• regulated excretion
• Insulin binds to insulin receptor -> sends an intracellular signal that causes glucose receptors to reloacte to the PM -> causes an influx of glucose into cell

Question 10

What are 4 examples of regulated exocytosis leading to plasma membrane enlargement?

Answer 10

Question 11

Secretion is _____ in polarized cells. How is this possible?

Answer 11

• directional
• The apical plasma membrane of epithelial cells have a different protein content than the basolateral plasma membrane

Question 12

What are two ways that polarized exocytosis and transcytosis occur?

Answer 12

Question 13

Apical sorting may involve lipid microdomains called lipid rafts. How?

Answer 13

Only proteins with longer transmembrane domains can go into the raft phase.

Question 14

Endocytosis

Answer 14

Internalization of external material including proteins located on the plasma membrane

Question 15

3 types of endocytosis?

Answer 15

1. Receptor-mediated endocytosis
2. phagocytosis
3. pinocytosis

Question 16

Receptor-mediated endocytosis

Answer 16

• Cellular uptake of macromolecules usually en route to the lysosome
• Ingestion of metabolites

– Cholesterol through LDL and the LDL receptor

– Iron via the transferrin receptor

• Termination of cell surface events (ie signaling)

Question 17

Phagocytosis

Answer 17

• “cellular eating”
• Ingestion of large particle such as microorganisms or dead cells (usually >250 nm in diameter)
• Usually triggered

Question 18

Pinocytosis

Answer 18

• “cellular drinking”

• Ingestion of fluids and solutes (~100 nm in diameter)
• Constitutive

Question 19

COPII coats vesicles in the ___

Answer 19

ER- heading out toward PM

Question 20

COPI coats vesicles in the ___

Answer 20

TGN- heading back towards ER

Question 21

Clathrin coats vesicles at the ___

Answer 21

PM, Early and late endosome

Question 22

Mechanism of endocytosis

Answer 22

• Coat proteins are used to deform the membrane and form a coated vesicle
  
  • primary coat protein is clathrin

Question 23

Clathrin coats are composed of ___

Answer 23

the clathrin complex (a triskelion-3 heavy chains and 3 light chains) and clathrin adaptors

Question 24

The diversity of clathrin coats (ie budding form different compartments) is generated by…

Answer 24

using different adaptors

Question 25

\_\_\_\_ proteins link integral membrane proteins to clathrin

Answer 25

Adaptor

Question 26

What is responsible for uncoating clathrin coated vesicles?

Answer 26

* “Uncoating ATPase” * Cytosolic HSP70 family member

Question 27

How does the clathrin adpator AP2 work?

Answer 27

* When AP2 is bound to phosphoinositides and cargo recpetors, it opens and allows clathrin to bind

Question 28

Unlike internal membranes, vesicles derived from the plasma membrane require help of \_\_\_\_\_for membrane fission

Answer 28

dynamin

Question 29

What is dynamin? Whar does it do?

Answer 29

• Dynamin is a GTPase that constricts the neck of the newly formed coated pit to form a vesicle

Question 30

Why do PM derived vesicles require the help of dynamin?

Answer 30

– Different phospholipid bilayer composition – Increased membrane stiffness – Regulation of internalization (sometimes a pit is good)

Question 31

Low density lipoprotein (LDL) particles are responsible for...

Answer 31

import of cholesterol esters into the cell

Question 32

How does import of extracellular cholesterol occur?

Answer 32

Question 33

What are the three potential fates of endocytosed membrane proteins?

Answer 33

1. degradation in the endolysosome 2. recycling 3. transcytosis

Question 34

\_\_\_\_\_ form as early endosomes mature to late endosomes.

Answer 34

* Multivesicular bodies (MVBs) * This process separates and sequesters material (particularly membrane proteins) to be degraded from material to be recycled.

Question 35

membrane proteins are marked for inclusion into MVBs by \_\_\_\_

Answer 35

ubiquitin, which detaches just before formation of intralumenal vesicles

Question 36

\_\_\_ proteins are responsible for sorting into and formation of MVBs

Answer 36

ESCRT

Question 37

MVB formation is the same process as \_\_\_\_

Answer 37

virus budding from the PM

Question 38

How does synaptic vesicle recycling occur?

Answer 38

Question 39

What are the specialized types of endocytosis?

Answer 39

* Phagocytosis * Pinocytosis * Transcytosis

Question 40

Phagocytosis occurs by...

Answer 40

psuedopod formation

Question 41

How are psuedopods formed?

Answer 41

Pseudopod formation is driven by actin polymerization and reorganization in response to specific phosphoinositide generation.

Question 42

Macropinocytosis

Answer 42

Question 43

What are caveolae?

Answer 43

Membrane invaginations, similiar to an endocytosed vesicle that has failed to detach from the PM