Vesicle Transport and Secretory Pathways

Question 1

Where are proteins that are destined for the secretory pathways translated?

Answer 1

By ribosomes on the ER membrane

Question 2

What directs proteins that are destined for secretory pathways to the ER?

Answer 2

a signal sequence

Question 3

Where does N-linked glycosylation of membrane proteins occur?

Answer 3

ER lumen

Question 4

Explain how N-linked glycoslyation occurs in the ER lumen

Answer 4

1. Protein must of the sequence Asn-X-Ser/Thr
2. A branched oligosaccharide linked to a membrane lipid looks for asparginine sequence
3. the branched oligosaccharide is transferred to the asparginine amide

Question 5

What is the purpose of N-linked surgar modifications?

Answer 5

1. Direct sorting to different parts of the cell

2. can be involved in Cell-cell recognition

Question 6

When does disulfide bond formation typically occur?

Answer 6

During or soon after synthesis

Question 7

What protein catalyzes breakage and reformation of disulfide bonds?

Answer 7

protein disulfide isomerase

Question 8

What is the purpose of the making and breaking of disulfide bonds done by protein disulfide isomerase?

Answer 8

it allows the protein to get into the most thermodynamically stable conformation

Question 9

What type of proteins typically have disulfide bonds?

Answer 9

secretory and membrane proteins

Question 10

What effect does the cytosol have on disulfide bond formation?

Answer 10

• Prevents formation

- This is because the cytosol is a reducing environment

Question 11

T or F: both properly and improperly folded proteins are transported out the ER

Answer 11

True

Properly folded proteins are transported out via formation of a vesicle

Improperly folded proteins are transported out via translocation channel

Question 12

What proteins that exist within the ER aid in protein folding?

Answer 12

Chaperones assist unfolded proteins in achieving the most thermodynamically stable conformation

Question 13

T or F: oligomeric proteins such as antibodies may be transferred out of the ER and assembled in the cytoplasm

Answer 13

False - the protein must be fully assembled before being transported out

Question 14

What happens to mis-folded proteins in the ER?

Answer 14

1. they are transported out via reverse transport through translocation channel
2. Deglycosylated and Ubiquitylated in the cytosol
3. Degraded by a proteasome

Question 15

What causes stimulation of chaperone synthesis?

Answer 15

• this is called the unfolded protein response

- occurs when unfolded proteins accumulated in the ER

Question 16

What diseases result from alpha anti-trypsin deficiency?

Answer 16

• Emphysema (major genetic cause)
• Liver disease
• hepatocellular carcinoma

Question 17

What is the job of alpha anti-trypsin ?

Answer 17

inhibition of elastase

Question 18

What types of cells typically secrete alpha anti-trypsin (3 types) ?

Answer 18

1. hepatocytes
2. macrophages
3. neutrophils

Question 19

What is the most common cause of alpha anti-trypsin deficiency?

Answer 19

• single AA change causes mis-folded protein

- protein is expelled from ER and degraded by proteasome

Question 20

What is caused by mutation F508del and why does this deletion cause disease?

Answer 20

• cystic fibrosis
• oligosaccharide side chains are not processed properly
• protein then misfolds and is degraded

Question 21

How are proteins transferred from the ER to the golgi, lysosomes, or plasma membrane?

Answer 21

Transport vesicles

Question 22

What is the job of protein coats in vesicular transport?

Answer 22

• Allows for selection of appropriate cargo proteins for transportation
• Form basket-like complexes that deform membrane before it pinches off into a vesicle

Question 23

What are 3 types of protein coats?

Answer 23

Clathrin
COPI
COPII

Question 24

In what types of vesicles is clathrin found?

Answer 24

1. exocytic formed at TRANS golgi network

2. Endocytic vesicles formed on the plasma membrane

Question 25

In what types of vesicles is COPI found?

Answer 25

1. vesicles moving through Golgi in an anterograde fashion | 2. vesicles formed on Golgi that are bound for ER membrane

Question 26

In what types of vesicles is COPII found?

Answer 26

Vesicles formed in ER that are bound for CIS-golgi

Question 27

What are the steps in clathrin-coated vesicle formation? Note: this serves as a general model for coat formation

Answer 27

1. clathrin triskelions form a basket-like structure 2. clathring lattice induces vesicle budding 3. Adaptin (contained on Clathrin coated vesicles) binds transmembrane prots. and cargo receptors 4. Dynamin (GTPase) works with other prots. to pinch of vesicle 5. vesicles loose prot. coat soon after pinching off

Question 28

What proteins mediate targeting of the vesicles?

Answer 28

Rabs Tethers SNAREs

Question 29

What proteins mediate initial vesicle recognition?

Answer 29

Rabs and Thethers bind to each other

Question 30

What do SNAREs do and how do they work?

Answer 30

- they ensure additional specificity 1. vSNARE (on vesicle) binds tSNARE (on target membrane) 2. The two interwrap pulling the membranes together promoting fusion

Question 31

T or F: the morphology of coats formed by COP proteins differs from the clathrin coat

Answer 31

True

Question 32

What protein coats allows for ER cargo receptors and other ER resident proteins to be returned to the ER?

Answer 32

COPI

Question 33

What allows for selectivity in COPII vesicle packaging?

Answer 33

Association of the ER proteins with cargo receptors

Question 34

Why does retrograde transport from golgi to ER occur and what protein mediates this movement?

Answer 34

- Occurs because ER needs to retrieve ER cargo receptors ans soluble ER resident proteins that were mis-sorted to the cis-Golgi - COPI mediates movement

Question 35

How does retrieval of transmembrane ER proteins occur?

Answer 35

Di-lysine sequence binds directly to the COPI coat

Question 36

How does retreival of lumenal ER proteins occur?

Answer 36

- mediated by ER retention signal (c-terminus KDEL) on the lumenal ER prot. binding to the KDEL receptor in cis-golgi membrane

Question 37

What happens to surgar modifications as proteins that have exited the ER move to the GolgI?

Answer 37

They pass through cisternae to the trans face and acquire increasingly complex sugar modifications

Question 38

Why does the golgi reside in the vicinity of the centrosome?

Answer 38

because its localization is dependent on microtubules

Question 39

What are the 3 regions make up the golgi, and what is the job of the golgi?

Answer 39

cis medial trans

Question 40

What is the golgi function?

Answer 40

sorting and glycosylation

Question 41

What are two real-time techniques that allow for visualization of sorting proteins?

Answer 41

1. GFP labeled proteins 2. Temperature sensitive mutants that have wild type activity at normal temperatures and defective at the restrictive temp

Question 42

Where do proteins exit the golgi, and what are the possible destinations for these proteins?

Answer 42

1. Plasma membrane 2. secretory vesicles 3. lysosomes

Question 43

Describe the default pathway for proteins targeted for the plasma membrane.

Answer 43

- no specific targeting sequence | - exocytosis occurs independent of any known stimulus

Question 44

Describe regulated secretion/exocytosis

Answer 44

1. vesicle contents are stored in special secretory vesicles | - these vesicles are released in response to nuerotransmiter or hormonal cell stimulation

Question 45

Describe the maturation process of secretory vesicles

Answer 45

- Mature vesicles have more densely packed protein | - Often maturation includes proteolytic processing

Question 46

What is famili hyperinsulinemia-an?

Answer 46

asymptomatic condition in which pro-insulin isn't cleaved this leads to a build of pro-insulin

Question 47

What coat proteins will be used on a vesicle traveling from the golgi to the lysosome via endosomes have?

Answer 47

clathrin + GGA adaptor

Question 48

What coat proteins will be used on a vesicle traveling from golgi to plasma membrane?

Answer 48

clathrin + adaptin 1

Question 49

What coat proteins will be used on a vesicle traveling from plasma membrane to endosomes?

Answer 49

clathrin + adaptin 2

Question 50

What coat proteins will be used on a vesicle traveling from ER to Golgi?

Answer 50

COPII

Question 51

What coat proteins will be used on a vesicle traveling from Golgi cisterna to golgi cisterna?

Answer 51

COPI

Question 52

What coat proteins will be used on a vesicle traveling from golgi to ER?

Answer 52

COPI

Question 53

What would occur if decoating of clathrin and COP coats did not occur after the vesicle was moved into the cytosol?

Answer 53

The proper recognition proteins would not be exposed and proteins would not go to the correct compartment

Question 54

What rab, vSNARE, and tSNAREs are involved in Ach release?

Answer 54

``` vSNARE = VAMP Rab = Rab3A tSNARE = syntaxin ```

Question 55

What is the retrieval signal for lumenal proteins that have been mistakenly transferred to the ER and how does this pathway work?

Answer 55

KDEL receptor binds to the KDEL sequence on the lumenal protein KDEL receptor then binds the COPI coat Binding the COPI coat induces budding so the vesicle can travel back to the ER

Question 56

What is the retrieval signal for transmembrane proteins that have been mistakenly transferred to the ER and how does this pathway work?

Answer 56

Transmembrane proteins contain a cytosolic di-lysine retreval signal COPI binds and returns vesicle

Question 57

What is the default pathway for proteins that lack a specific signal on the vesicle?

Answer 57

Constitutive secretion | This uses Clathrin + AP1 to send localize the vesicle to the plasma membrane and send the protein out of the cell

Question 58

What does regulated secretion depend on in order to occur?

Answer 58

signals such as hormones or neurotransmitter | Uses Clathrin + AP1

Question 59

What protein carries vesicles to the synapse in an axon and what is this protein dependent on?

Answer 59

Kinesin = ATP depedent

Question 60

What type of cytoskeletal structure is dependent on ARP and Rac?

Answer 60

Lamellipodial actin

Question 61

What do Taxol and Pacitaxel do?

Answer 61

Stabilize microtubules, preventing disassembly

Question 62

What neurotransmitter's release is dependent on Syntaxin and VAMP?

Answer 62

Ach (syntaxin = tSNARE, VAMP = vSNARE)

Question 63

What arrests translation of nascent proteins by recognizing a hyrdophobic signal sequence?

Answer 63

SPR - signal recognition particle

Question 64

Explain how chaperon transcription can be upregulated by unfolded protein

Answer 64

1. Protein binds receptors with a cytoplamic kinase 2. Kinase phosphorylates transcription factor(s) 3. Factor goes into the nucleus and activates the chaperon gene