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Biology 360 > Topic 4C - Lysosomes and Endo/exocytosis > Flashcards

Topic 4C - Lysosomes and Endo/exocytosis Flashcards

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1
Q

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

A

It’s orientation is maintained: outside will face outside

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2
Q

What are 3 key characteristics of healthy vesicular transport?

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

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

A

3, 4 and 5

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4
Q

The primary role of phosphatidylinositols and phosphoinositides are…

A

Acting as membrane markers

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5
Q

What is the difference between phosphatidylinositiols and phosphoinositides?

A

Phosphoinositides are phosphorylated

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6
Q

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

A

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

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7
Q

What side of the membrane do phosphoinositides appear on?

A

The intracellular membrane

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8
Q

How do PIPs inform specificity of vesicle content?

A

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

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9
Q

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

A

Clathrin
COPI
COPII

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10
Q

What are the 2 key functions of the vesicle coat?

A
  1. Concentrate specific membrane proteins

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

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11
Q

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

A

Triskelion

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12
Q

Describe the number of chains within a clathrin molecule

A

3 heavy chains and 3 light chains

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13
Q

What molecule acts as an ATPase to uncoat vesicles?

A

Hsp70

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14
Q

Do clathrin coated vesicles always pack the same molecules?

A

No

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15
Q

Does clathrin bind directly to the vesicle membrane?

A

No - binds to adaptor protein

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16
Q

What causes the deformation of the membrane during vesicle formation?

A

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

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17
Q

What are Sec23 and Sec 24?

A

COPII adaptor coat proteins which form the inner coat

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18
Q

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

A

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

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19
Q

What is the monomeric GTPase associated with COPII coat formation?

A

Sar1

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20
Q

What is the monomeric GTPase associated with COPI coat assembly?

A

Arf1

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21
Q

What is the monomeric GTPase associated with clathrin coat assembly?

A

Arf1

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22
Q

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

A

The curvature of the membrane

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23
Q

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?

A

Yes

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24
Q

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

A
  1. Bind cargo receptors
  2. Collect specific proteins
  3. Help to bend the membrane
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25
Q

Describe the adaptor proteins of COPI vesicles

A

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

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26
Q

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

A

Rab

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27
Q

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

A

Rab effector

28
Q

How many polypeptide chains make up v-SNARE?

A

One

29
Q

How many polypeptide chains make up t-SNARE?

A

2 or 3

30
Q

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

A

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

31
Q

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

A

The trans snare complex

32
Q

Bacterial tetanus targets this protein

A

SNARE proteins

33
Q

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

A

Cytosolic membranes fuse first

34
Q

What can be a point of control in vesicle docking?

A

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

35
Q

Are all proteins in the ER packed into vesicles?

A

No, some stay in the ER

36
Q

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

A

COPII

37
Q

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

A

An ER exit signal

38
Q

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

A

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

39
Q

Describe the affinity for the KDEL receptor for COPI and COPII

A

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

40
Q

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

A
  1. SNARE complex

2. Rab proteins

41
Q

What is the “cis” face of the golgi?

A

The side where ER vesicles enter the golgi

42
Q

What is the “trans” face of the golgi?

A

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

43
Q

Describe the distribution of enzymes in the Golgi

A

Enzymes are area-specific, concentrated into a zone

44
Q

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

A

Modification of sugar groups

45
Q

What is a complex oligosaccharide?

A

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

46
Q

What is a high-mannose oligosaccharide?

A

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

47
Q

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

A

A high-mannose oligosaccharide

48
Q

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

A

A complex oligosaccharide

49
Q

Can a protein have more than one oligosaccharide chain?

A

Yes

50
Q

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

A

Glycosyl transferases

51
Q

What are 4 roles of glycosylation?

A
  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)
52
Q

What is the lysosome equivalent in plants?

A

Vacuole

53
Q

Lysosomal membrane proteins are mostly this kind of transmembrane protein

A

Transporters

54
Q

What kind of enzymes are commonly contained in lysosomes?

A

Proteolytic enzymes, hydrolytic enzymes, acid hydrolases

55
Q

What activates an enzyme in the lysosome?

A

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

56
Q

How is the inside of the lysosome protected against autodigestion?

A

Glycosylated proteins keep proteases away

57
Q

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

A

H+ pump, V-type ATPases

58
Q

Organelles are degraded through a process called…

A

Autophagy

59
Q

What organelle is responsible for autophagy?

A

Lysosomes

60
Q

What is transcytosis?

A

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

61
Q

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

A

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

62
Q

What 2 biochemical events occur in vesicles?

A
  1. Cargo concentration

2. Proteolytic processing

63
Q

Describe the primed state of synaptic vesicles ready for fusion

A

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

64
Q

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

A
  1. Cytokinesis
  2. Phagocytosis
  3. PM repair
  4. Cellularization
65
Q

An example of a tissue that undergoes cellularization is…

A

Fly embryonic tissues

Biology 360 (12 decks)

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