Vesicular Traficking IV (Lecture 17)

Question 1

What are the four steps in clathrin coated vesicular trafficking?

Answer 1

1. Clathrin/ AP2-coated pits form
2. Dynamin pinches off clathrin-coated vesicle
3. Vesicle free in cytoplasm (will uncoat to expose vSNARES and Rab proteins)
4. Vesicle fuses with endosome (~6 min after internalization began)

Question 2

______ transport mostly triglycerides from diet.

Answer 2

Chylomicrons

Question 3

______ synthesize and released by liver to transport triglycerides made by liver; cells remove the triglycerides

Answer 3

VLDL

Question 4

______ are less healthy and deliver cholesterol to the tissue.

Answer 4

LDL

Question 5

______ are healthy and return excess cholesterol from tissues and take it back to the liver.

Answer 5

HDL

Question 6

True or False: More dense means highest in proteins; less dense means highest in lipids.

Answer 6

True

Question 7

Where is the most cholesterol contained?

Answer 7

LDL

Question 8

What is the order of LDL uptake into cells in the Pulse-Chase experiment?

Answer 8

Surface binding of LDL —> Internalization —> Degradation

Question 9

______ receptor is a 839-residue glycoprotein (after removal of signal peptide) with a single transmembrane segment

Answer 9

LDL

Question 10

True or False: The LDL receptor has a short C-terminal cytosolic segment — and a long N-terminal exoplasmic segment contains LDL-binding domain.

Answer 10

True

Question 11

What does the long N-terminal of the LDL receptor binding domain contain?

Answer 11

Has seven cysteine-rich repeats; these interact with the apoB-100 molecule of the LDL particle

Question 12

True or False: After LDL reaches lysosomes, lysosomal proteases and esterases hydrolyze apoB-100 and cholesterol esters, respectively and then unesterified cholesterol then ready for use by the cell.

Answer 12

True

Question 13

What is the key step in LDL endocytosis?

Answer 13

Cell-surface LDL receptor binds to LDL particle.

Question 14

In the first step in LDL endocytosis, what pH is needed to bind another LDL particle?

Answer 14

neutral

Question 15

In the first step, the cytosolic tail with ______ sorting signal interacts with AP2 complex and incorporates the LDL-LDL receptor complex into clathrin-coated pit.

Answer 15

NPXY

Question 16

What are the other four steps in LDL endocytosis?

Answer 16

2.  Dynamin pinches off clathrincoated vesicle, then vesicle uncoats
3.  Vesicle fuses with endosome
•  Endosome acidic pH causes receptor conformational change to release LDL particle
4.  Late endosome fusion with lysosome
  LDL particle is broken down to constituent parts by lysosomal enzymes
5.  LDL receptor is recycled to the cell surface
•  LDL receptor round trip ~10–20 minutes

Question 17

What are the 3 types of sorting signals for endocytosis of clathrin/AP2-coated pits?

Answer 17

NPXY Asn-Pro-X-Tyr

YXXΦ

Covalently linked ubiquitin

Question 18

True or False: Covalently linked ubiquitin plays role in delivering these proteins to the lysosome, where they are degraded.

Answer 18

True

Question 19

What happens to LDL receptor at neutral pH?

Answer 19

Ligand binding arm tightly binds to LDL apoB-100

Question 20

What happened to LDL receptor at acidic pH.

Answer 20

Surface of B-propeller domain becomes positively charged, and then binds to the ligand-binding arm

Question 21

Familial ______ is a hereditary disease characterized by high plasma LDL levels

Answer 21

hypercholesterolemia

Question 22

What is the receptor ligand complex that functions to deliver iron to cells by changes in pH to sort receptors and ligand?

Answer 22

transferrin-transferrin

Question 23

\_\_\_\_\_\_ = transports iron in blood 
\_\_\_\_\_\_ = ‘empty’ transferrin (no iron bound) 
\_\_\_\_\_\_  = ‘full’ transferrin (two Fe3+ bound) 
\_\_\_\_\_\_ = binds ferrotransferrin and initiates endocytosis

Answer 23

Transferrin

Apotransferrin

Ferrotransferrin

Transferrin receptor

Question 24

How does the transferrin cycle work?

Answer 24

Ferrotransferrin binds to transferrin receptor

Transferrin receptor the n binds to clathrin coated receptor (dynamin pinches off)

Clathrin dissociates (ARF)

Vesicle binds to late endosome and low pH causes release of Fe from ligand, ligand is still bound to receptor)

Apotransferrin is recycled to cell surface

Apotransferrin dissociated from receptor at neutral pH

Question 25

______ degrade extracellular materials taken up by the cell.

Answer 25

Lysosomes

Question 26

True or False: The lumen of lysosomes contain degradative enzymes.

Answer 26

True

Question 27

How do materials needed to be degraded get delivered to lysosome?

Answer 27

Usually by fusion of a late endosome or phagosome with a lysosome

Question 28

True or False: Multivesicular endosomes are separated into specialized vesicles that form at endosomal membrane.

Answer 28

True

Question 29

Normal transport vesicles bud ______ from organelle membrane into cytosol.

Answer 29

Outward

Question 30

Internal vesicles bud ______ from endosomal membrane to lumen.

Answer 30

Inward

Question 31

True or False: Most cargo proteins destined to enter a multivesicular endosome (for degradation by lysosome) are tagged with a single ubiquitin molecule.

Answer 31

True

Question 32

Where can ubiquitin be attached at?

Answer 32

Plasma membrane, trans-Golgi network, or endosomal membrane

Question 33

What type of retrovirus complex requires ESCRT complex?

Answer 33

HIV

Question 34

The ______ pathway serves to recycle macromolecules for use as nutrients under stressful/starvation conditions.

Answer 34

Autophagy

Question 35

How does autophagy pathway work?

Answer 35

Autophagosome engulfs organelle

Lysosomal contents degrade the autophagosome and amino acid permeases in lysosomal membrane transport amino acids back to cytosol