Intracellular Vesicular Transport

Question 0

Three types of coated vesicles

Answer 0

Clathrin
COPI
COPII

Question 1

Three steps of vesicular transport

Answer 1

Particular region of membrane pinches off to form coated vesicle
Vesicle finds and docks on its target compartment
Fusion of the membranes from the vesicle and target compartment

Question 2

Where do clathrin coated vesicles transport to/from?

Answer 2

From golgi to ER
from plasma
Endosomes as well

Question 3

Where does COPI transport from/to?

Answer 3

From Golgi to ER

Question 4

Where does COPII transport from/to?

Answer 4

From ER to golgi

Question 5

Describe the structure made by clathrin

Answer 5

Three heavy chains and three light chains that form a three legged structure called a triskelion

Question 6

What is adaptin?

Answer 6

Coat protein that function as link between clathrin and various transmembrane receptors. At least 4 types specific for different set of cargo receptors

Question 7

What is dynamin?

Answer 7

A GTP-ase that helps the clathrin coated vesicle bud

Question 8

When is the clathrin coat lost?

Answer 8

Shortly after budding

Question 9

ARF protein does what?

Answer 9

Helps with assembly of COPI and clathrin coat assemblies. GTPase

Question 10

Sar1 protein does what?

Answer 10

GTPase required for COPII coated vesicle formation

Question 11

What three complexes guide transport vesicles to target membranes?

Answer 11

t-SNARE, v-SNARE, and GTPase Rabs

Question 12

What is the SNARE hypothesis?

Answer 12

v-SNARE (vesicle) and t-SNARE (target) are complementary. The fitting together is monitored by GTPase Rab protein. When docking connection lasts long enough, Rab is able to hydrolyze its GTP to GDP leading to a lock of the vesicle. NSF then induces the two membranes to fuse.

Question 13

What is required to separate fused SNAREs?

Answer 13

NSF, pries apart interacting SNAREs so they can be used again

Question 14

How to viruses fuse into cells?

Answer 14

Chemokine interaction with the virus allows for membrane insertion ad fusion of the membrane and nucleocapsid release into cell

Question 15

Transport from the ER is mediated by what coat protein?

Answer 15

COPII

Question 16

COPII coated vesicles do what?

Answer 16

Quickly shed coat after formation and then quickly fuse together on their way to the cis-golgi network

Question 17

Retrieval of soluble ER resident proteins back to the ER is accomplished by?

Answer 17

KDEL receptors

Question 18

As we move from ER towards the trans Golgi network, the pH gets?

Answer 18

More acidic

Question 19

How is retrograde ER transport acheived?

Answer 19

KDEL signals (lys-asp-glu-leu) bind to KDEL receptors and are packaged into COPI coated vesicles and move back to Golgi. KDEL sequence on C-terminal

Question 20

Describe the constitutive secretory pathway

Answer 20

Default pathway of protein secretion. Used by all cells. Supplies plasma membrane proteins and lipids. Involved in exocytosis

Question 21

Describe the regulated secretory pathway

Answer 21

Specialized secretory cells sort proteins and selective package them into secretory vesicles at the TGN through clathrin coated vesicles. Proteins are greatly condensed and proteolytic cleavage occurs. These are released upon trigger

Question 22

Membrane recycling is facilitated by what coat?

Answer 22

Clathrin

Question 23

Where are proteins concentrated into vesicles?

Answer 23

TGN

Question 24

Three best understood pathways of protein sorting in the TGN

Answer 24

Signal mediated diversion to lysosomes Constitutive secretory pathway Signal mediated diversion to secretory pathway

Question 25

What are synaptogamin and syntaxin?

Answer 25

The v-SNARE and t-SNARE equivalents, respectively, at the synapse

Question 26

What is Rab3?

Answer 26

A synaptic vesicle specific G-protein

Question 27

Two types of endocytosis

Answer 27

Phagocytosis | Pinocytosis

Question 28

Where does phagocytosis occur?

Answer 28

Macrophages and neutrophils

Question 29

T or F: Receptor mediated endocytosis occurs in coated pits

Answer 29

T, usually clathrin

Question 30

T or F: Pinocytosis occurs in all cells

Answer 30

T, except for RBC or other few exceptions

Question 31

What is non-selective pinocytosis?

Answer 31

Fluid phase uptake of ECM

Question 32

What is receptor-mediated pinocytosis?

Answer 32

Take up of macromolecules

Question 33

Describe receptor mediated endocytosis of LDL

Answer 33

Binding of LDL to receptor in clathrin coated pit. Pinched off. Uncoating. Fusion with endosome. Separation of LDL from receptor. Aggregation of receptor to endosome to return to membrane. Transfer of LDL to lysosome. Degradation of apo B and cholesterol ester leading to reduction in HMG-CoA reductase and receptor number

Question 34

One receptor mediated defect in familial hypercholesteremia

Answer 34

LDL receptor does not accumulate in clathrin pit. Mutations in cytoplasmic domain.

Question 35

What sequence is required for LDL clathrin interaction?

Answer 35

Phe-Arg-X-Tyr on the C-terminus of LDL for adaptin binding

Question 36

Three outcomes of endocytosis

Answer 36

``` Receptor recycles (LDL, transferrin) Receptor degraded (ligand too) Transcytosis (Epithelial cells transfer from one ECM to other) ```

Question 37

Describe transferrin pathway

Answer 37

Transferrin binds Fe ions in ECM at 7 pH. Loaded and delivers to endosome. Acidic pH dissociates to apotransferrin. Apotransferrin brought back to surface. Iron released to cell

Question 38

Describe how IgG gets from mom to baby

Answer 38

Transcytosis to the ECM through epithelial out from intestinal lumen. Gut is 6.0 and ECM is 7.0. Binds at low pH and released at high pH

Question 39

T or F: Growth factor receptors are recycled

Answer 39

F, not usually

Question 40

Describe EGFR process

Answer 40

not in coated pits de-facto, dimerize with ligand, both are degraded. This is down-regulation. Only accumulate in pits following dimerization

Question 41

Describe maturation of endosome from plasma membrane on

Answer 41

Early endosome, Late endosome, endolysosome, lysosome

Question 42

What is a lysosome?

Answer 42

Contains wide range of hydrolases. All acidic. pH optimum around 5.

Question 43

Three pathways to degradation in lysosomes

Answer 43

Endocytosis Phagocytosis Autophagy

Question 44

How are lysosomes formed?

Answer 44

Lysosomal proteins synthesized in the RER and transported through golgi. Tagged with mannose-6-phosphate on the N-terminal in the cis-Golgi by N-acetylglucosaminephosphotransferase and N-acetylglucosaminylphosphodiesterase

Question 45

What protein coats lysosomes from the TGN?

Answer 45

Clathrin

Question 46

What is inclusion cell disease?

Answer 46

Faulty lysosomal targeting. Lack of GlcNAc-phosphotransferase (first step of mannose-6-P). Lysosomal enzymes are secreted out of cell by default pathway