Week 2 Vesicular Transport Module

Question 1

what are three functions of vesicular transport?

Answer 1

deliver newly made molecules to their final destinations, communicate with the extracellular environment, ingest extracellular particles and solutes.

Question 2

What are the two major pathways of vesicular transport

Answer 2

secretory pathway and the endocytic pathway

Question 3

what is the function of the secretory pathway

Answer 3

delivers newly made molecules to their proper position outside the cell

Question 4

what is the function of the endocytic pathway

Answer 4

delivers extracellular components to the inside of the cell

Question 5

where does secretory vesicular transport begin?

Answer 5

ER

Question 6

In general vesicles ____ off the _______ and fuse to the _______ while carrying _____

Answer 6

bud, donor compartment, target compartment, cargo

Question 7

describe the role of protein coating in vesicle budding. what two functions does the coat play?

Answer 7

vesicles require a protein coat for budding. the protein coat helps pinch vesicle off donor membrane and helps sort sort the cargo

Question 8

what are the three major protein coating proteins?

Answer 8

clathrin, COPI and COPII

Question 9

Describe the structure of clathrin. how does this relate to function?

Answer 9

3 heavy chains and 3 light chains form a triskelion which forces vesicle into rounded shape.

Question 10

How does clathrin bind the membrane of budding vesicles? (what is the binding cascade?)

Answer 10

Clathrin binds adaptin, adaptin binds cargo receptor, cargo receptor binds cargo

Question 11

What is the role of dynamin in vesicle formation?

Answer 11

pinches off vesicle

Question 12

what accounts for the variation in cargo carried by vesicles?

Answer 12

different adaptin molecules bind different cargo receptors in different regions of the cell.

Question 13

What happens to the clathrin coat prior to the vesicle reaching the target compartment?

Answer 13

clathrin and adaptin are released from the vesicle and recycled

Question 14

how does the vesicle find its way to the target compartment?

Answer 14

it moves along cytoskeletal elements within the cytoplasm

Question 15

which proteins are responsible for docking and recognition of vesicles to target compartments?

Answer 15

Rab located on the vesicle binds the tethering protein located on the target membrane

Question 16

which proteins are largely responsible for the fusion of the vesicle with the target membrane?

Answer 16

v-snare on the vesicle and t-snare on the target compartment

Question 17

What types (3) of modifications or proteins occur in the ER?

Answer 17

Cys-Cys Disulfide bonds (interchain and intrachain)

lipid membrane anchors (addition of lipids that covalently anchor protein to the membrane

The initial glycosylation of proteins occurs in the ER

Question 18

Oligosaccharides are generally added to which residues on a polypeptide chain?

Answer 18

Asparagine (Asn)

Question 19

what is the difference between N-lonked and O-linked glycoproteins?

Answer 19

N-linked: oligasaccharide added to Asn residue

O-linked: added to Ser or Threonine

Question 20

what is the role of dolichol?

Answer 20

dolichol is a special membrane lipid in the ER that transfers its oligasaccharide group to the newly translated polypeptide

Question 21

Describe the selectivity of exit from the ER

Answer 21

protein exit from the ER is highly selective. The ER uses chaperone proteins to ensure proteins fold correctly. If a protein cant be made to fold correctly it is degrade in cytosol

Question 22

what is the difference between cis-golgi network and trans-golgi network?

Answer 22

Cis: where vesicles enter the golgi

Trans: where vesicles exit the golgi

Question 23

Vesicles that exit the golgi are destined to go where?

Answer 23

endosome or plasma membrane

Question 24

as a vesicle moves through the golgi what happens to its contents?

Answer 24

further sorting and modification of sugars and proteins

Question 25

What are the two pathways of exocytosis

Answer 25

constitutive secretion, regulated secretion

Question 26

describe constitutive secretion. what cells do this? role?

Answer 26

constantly occuring and seen in all cells. supplies PM with new proteins and lipids and releases things to extracellular space

Question 27

describe regulated secretion. what cells do this? role?

Answer 27

release of vesicle contents to extracellular space in response to specific stimulus (receptor activation). only seen ins specialized secretory cells such as endocrine cells

Question 28

what is the pathway of an ER protein from the ER to lysosome?

Answer 28

ER–>cis golgi–>trans golgi–>endosome–>lysosome

Question 29

what is the role of lysosome? what type of enzymes to they house?

Answer 29

sites of molecular degradation. House acid hydrolases (nucleases, proteases, lipases)

Question 30

describe the pH of a lysosome. how is it maintained?

Answer 30

acidic (pH about 5. compare to pH 7.2 see in cytosol). maintained through hydrogen pumps

Question 31

where are all lysosomal proteins translated?

Answer 31

by ER bound ribosomes

Question 32

what protects acid hydrolases from the acidic environment of the lysosome?

Answer 32

acid hydrolases are heavily glycosylated in the ER to protect them from the low pH

Question 33

what is the role of Mannose-6-phosphate? where is it added?

Answer 33

Mannose-6-phosphate is added to lysosomal acid hydrolases within the GOLGI. M6P binds M6P receptors of clathrin coated vesicles. These vesicles are targeted to endosomes.

Question 34

compare early and late endosomes. Location? Acidity?

Answer 34

early: located near PM, slightly acidic (pH of 6.2)
late: located in interior of cell, more acidic (pH of 5.5). will mature into lysosome

Question 35

what is I-cell disease? cause? results?

Answer 35

enzyme that adds M6P (within golgi) is defective. therefore acid hydrolases are not targeted to endosomes and end up in blood.

Question 36

What are the three types of endocytosis?

Answer 36

phagocytosis, pinocytosis, receptor-mediated endocytosis

Question 37

What is phagocytosis? where is it seen?

Answer 37

ingestion of large particles (bacteria and cell debris). immune cells

Question 38

what is pinocytosis? where is it seen?

Answer 38

ingestion of fluid and small molecules. seen in all cells

Question 39

What is receptor-mediated endocytosis? what does it accomplish?

Answer 39

a mechanism that allows concentrated uptake of specific molecules

Question 40

what offsets the loss of membrane through pinocytosis?

Answer 40

constiutive secretion

Question 41

is pinocytosis clatherin dependent?

Answer 41

it can be, but not always

Question 42

describe the process of receptor-mediated endocytosis

Answer 42

specific cargo bind cargo receptors on (facing extracellular space)–>clathrin coated pits are formed (adaptin binds cargo receptor, clathrin binds adaptin)–> the vesicle buds INTO the cell and is ready to fuse

Question 43

What is the role of early endosomes?

Answer 43

sort endocytosed material

Question 44

what are the fates of receptors used in receptor mediated endocytosis?

Answer 44

1. recycled to PM
2. degraded by lysosome
3. transocytosis: travel across a cell

Question 45

how does the cargo know to release when it contacts an early endosome? what if it doesnt release?

Answer 45

the light acidic pH of the early endosome triggers cargo release. If the cargo is not released it will have the same fate as the receptor.

Question 46

how is cholesterol transported in blood?

Answer 46

transported as LDL: a core of cholesterol with a lipid monolayer that is organized by a protein.

Question 47

How do cells take in cholesterol from blood?

Answer 47

LDL receptors locate LDL and entire LDL molecule is taken up (receptor mediated endocytosis)

Question 48

what is familial hypercholesterolemia caused by?

Answer 48

mutation in LDL receptor that results in excess LDL cholesteron in blood