Topic 4C - Lysosomes and Endo/exocytosis

Question 1

What is true of orientation of a membrane-bound protein when it undergoes vesicular transport?

Answer 1

It’s orientation is maintained: outside will face outside

Question 2

What are 3 key characteristics of healthy vesicular transport?

Answer 2

1. Organized - they know where to go
2. Balanced
3. Selective

Question 3

In a phosphatidyl inositol molecule, which positions on the inositol ring can be phosphorylated?

Answer 3

3, 4 and 5

Question 4

The primary role of phosphatidylinositols and phosphoinositides are…

Answer 4

Acting as membrane markers

Question 5

What is the difference between phosphatidylinositiols and phosphoinositides?

Answer 5

Phosphoinositides are phosphorylated

Question 6

Remember that sugars can only exist on the outside of a membrane, What is special about inositol head of phosphoinositides?

Answer 6

It appears to be a sugar but is actually a sugar alcohol, therefore it can be on the inside of membranes

Question 7

What side of the membrane do phosphoinositides appear on?

Answer 7

The intracellular membrane

Question 8

How do PIPs inform specificity of vesicle content?

Answer 8

PIPs serve as docking sites for molecules, depending on which positions of the inositol are phosphorylated, different molecules will bind to them, so they are helpful for selectivity when loading vesicles

Question 9

What are the 3 key coat proteins discussed in this course?

Answer 9

Clathrin
COPI
COPII

Question 10

What are the 2 key functions of the vesicle coat?

Answer 10

1. Concentrate specific membrane proteins

2. Help to form vesicles by initiating bending of the membrane

Question 11

What is the name of the “3-legged” structure of clathrin?

Answer 11

Triskelion

Question 12

Describe the number of chains within a clathrin molecule

Answer 12

3 heavy chains and 3 light chains

Question 13

What molecule acts as an ATPase to uncoat vesicles?

Answer 13

Hsp70

Question 14

Do clathrin coated vesicles always pack the same molecules?

Answer 14

No

Question 15

Does clathrin bind directly to the vesicle membrane?

Answer 15

No - binds to adaptor protein

Question 16

What causes the deformation of the membrane during vesicle formation?

Answer 16

Integration of cargo receptors and adaptor proteins into the membrane creates ELECTROSTATIC INTERACTIONS where the membrane is attracted to the coat proteins

Question 17

What are Sec23 and Sec 24?

Answer 17

COPII adaptor coat proteins which form the inner coat

Question 18

What causes Sar1-GDP to bind to the pre-vesicle membrane?

Answer 18

Interacts with a Sar1-GEF which converts it to Sar1-GTP which exposes its amphipathic helix to associate with the membrane

Question 19

What is the monomeric GTPase associated with COPII coat formation?

Answer 19

Sar1

Question 20

What is the monomeric GTPase associated with COPI coat assembly?

Answer 20

Arf1

Question 21

What is the monomeric GTPase associated with clathrin coat assembly?

Answer 21

Arf1

Question 22

What activates the GAP for Arf1 (which will cause the coat to disassemble)

Answer 22

The curvature of the membrane

Question 23

Does the affinity to the membrane of monomeric GTPases associated with vesicle coats when there is a polar substitution of a residue in the amphipathic helix?

Answer 23

Yes

Question 24

What are the 3 functions of adaptor proteins in clathrin coats?

Answer 24

1. Bind cargo receptors
2. Collect specific proteins
3. Help to bend the membrane

Question 25

Describe the adaptor proteins of COPI vesicles

Answer 25

There are no adaptor proteins, adaptor proteins are exclusive to clathrin-coated vesicles

Question 26

The GTPase responsible for transport into vesicles, vesicle formation, and finding the correct vesicle target is...

Answer 26

Rab

Question 27

Rab-GTP makes initial contact with the target membrane by interacting with...

Answer 27

Rab effector

Question 28

How many polypeptide chains make up v-SNARE?

Answer 28

One

Question 29

How many polypeptide chains make up t-SNARE?

Answer 29

2 or 3

Question 30

What does it mean for the fusion of membranes to be heterotypic?

Answer 30

Two different kinds of membrane fuse together (e.g. ER and Golgi membranes fusing)

Question 31

Together, v-SNARE and t-SNARE complexes form...

Answer 31

The trans snare complex

Question 32

Bacterial tetanus targets this protein

Answer 32

SNARE proteins

Question 33

When two membranes are interacting and about to fuse, which membranes fuse first?

Answer 33

Cytosolic membranes fuse first

Question 34

What can be a point of control in vesicle docking?

Answer 34

Formation of the SNARE complex and its accessory proteins, if it is not formed then vesicles cannot dock

Question 35

Are all proteins in the ER packed into vesicles?

Answer 35

No, some stay in the ER

Question 36

What kind of coat forms around vesicles going from the ER to the Golgi?

Answer 36

COPII

Question 37

In order for an ER protein to bind to a cargo receptor, it must have...

Answer 37

An ER exit signal

Question 38

Why is it necessary to have different kinds of coats such as COPI and COPII?

Answer 38

They bind different "adaptors" so that different cargo can be loaded, has different affinity for different cargo

Question 39

Describe the affinity for the KDEL receptor for COPI and COPII

Answer 39

KDEL wants to stay in ER COPII = away from ER COPI = back to ER Needs high affinity to COPI cargo receptors and low affinity for COPII receptors

Question 40

What determines the fusion of a vesicle to its correct membrane target? (2)

Answer 40

1. SNARE complex | 2. Rab proteins

Question 41

What is the "cis" face of the golgi?

Answer 41

The side where ER vesicles enter the golgi

Question 42

What is the "trans" face of the golgi?

Answer 42

The side of the Golgi sending contents away from ER to lysosome, PM, etc.

Question 43

Describe the distribution of enzymes in the Golgi

Answer 43

Enzymes are area-specific, concentrated into a zone

Question 44

What is the major biochemical modification to proteins that occurs in the ER?

Answer 44

Modification of sugar groups

Question 45

What is a complex oligosaccharide?

Answer 45

An oligosaccharide chain which was trimmed and then had sugars added to it

Question 46

What is a high-mannose oligosaccharide?

Answer 46

An oligosaccharide which was trimmed so the terminal branches all end in mannose sugars

Question 47

When an untrimmed glycoprotein has its saccharide group in an inaccessible place (i.e. the inside of a protein) the chain will be...

Answer 47

A high-mannose oligosaccharide

Question 48

When an untrimmed glycoprotein has its oligosaccharide group in an accessible place, it is likely that the chain will be...

Answer 48

A complex oligosaccharide

Question 49

Can a protein have more than one oligosaccharide chain?

Answer 49

Yes

Question 50

What enzyme is responsible for adding sugars to glycoproteins in the golgi?

Answer 50

Glycosyl transferases

Question 51

What are 4 roles of glycosylation?

Answer 51

1. Promotes correct folding of a protein 2. Helps keep proteolytic enzymes away (scaffold) 3. Cell-cell recognition 4. Sugars can be functional (e.g. mucous in stomach)

Question 52

What is the lysosome equivalent in plants?

Answer 52

Vacuole

Question 53

Lysosomal membrane proteins are mostly this kind of transmembrane protein

Answer 53

Transporters

Question 54

What kind of enzymes are commonly contained in lysosomes?

Answer 54

Proteolytic enzymes, hydrolytic enzymes, acid hydrolases

Question 55

What activates an enzyme in the lysosome?

Answer 55

Proteolytic cleavage - this explains why the proteins were able to be in the ER/Golgi without destroying anything

Question 56

How is the inside of the lysosome protected against autodigestion?

Answer 56

Glycosylated proteins keep proteases away

Question 57

In order to acidify lysosomes, this kind of pump can be used

Answer 57

H+ pump, V-type ATPases

Question 58

Organelles are degraded through a process called...

Answer 58

Autophagy

Question 59

What organelle is responsible for autophagy?

Answer 59

Lysosomes

Question 60

What is transcytosis?

Answer 60

Delivery of a cellular protein from the apical to basal sides, typically in an asymmetrical cell like a neuron

Question 61

What are the typical 3 destinations for cells leaving the trans golgi network?

Answer 61

Lysosomes Constitutive secretory pathway (normal secretion) Signal-mediated diversion to secretory vesicles (regulated secretion)

Question 62

What 2 biochemical events occur in vesicles?

Answer 62

1. Cargo concentration | 2. Proteolytic processing

Question 63

Describe the primed state of synaptic vesicles ready for fusion

Answer 63

Vesicular pool: Snare bundles ready for docking and fusion but complexin blocks full fusion

Question 64

What are 4 cases where the plasma membrane might need to be enlarged?

Answer 64

1. Cytokinesis 2. Phagocytosis 3. PM repair 4. Cellularization

Question 65

An example of a tissue that undergoes cellularization is...

Answer 65

Fly embryonic tissues