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Molecular Biology - Unit 2 - Zach H. > Intracellular Vesicular Traffic 2 > Flashcards

Intracellular Vesicular Traffic 2 Flashcards

1
Q

What are lysosomes?

A

Membrane enclosed compartments filled with hydrolytic enzymes.

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2
Q

What are lysosomes derived from?

A

Heterogeneous - derived from late endosomes.

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3
Q

What are lysosomes important for?

A

Intracellular digestion of macromolecules.

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4
Q

How many different types of enzymes are found in lysosomes?

A

About 40:

  • proteases
  • mucleases
  • glycosidases
  • lipases
  • phospholipases
  • phosphatases
  • sulfatases
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5
Q

What is required for optimal activation of lysosomes?

A

acidic environment and proteolytic cleavage

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6
Q

What happens to the end products of digestion in the lysosome?

A

Transporters in membrane pump out end products.

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7
Q

How is the acidic pH in lysosomes maintained?

A

Vacuolar ATPase pumps H+ into lysosomes.

also to drive transport of small metabolites

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8
Q

Approximately what is the pH in the lysosome?

A

pH of about 5

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9
Q

How can histochemical visualization of lysosomes be achieved?

A

by staining the acid phosphatases

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10
Q

What is the order of lysosome maturation starting at the plasma membrane?

A 
- early endosome
     > microtubule-mediated transport
- late endosome
- endolysosome 
- lysosome
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11
Q

List the multiple pathways that deliver materials to lysosomes.

A

> phagocytosis
endocytosis
autophage from mitochondrion
macropinocytosis (“cell drinking”)

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12
Q

Of the multiple pathways for material to get to the lysosome for degradation, which two pathways do not go through the late endosome process?

A

Autophagy –> turns into autophagosome and goes straight to fuse with lysosome.

Phagocytosis –> forms phagosome and goes straight to fuse with lysosome.

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13
Q

Regarding the model of autophage, list the steps in this mechanism.

A

> nucleation and extension
closure
fusion with lysosome
digestion

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14
Q

Where are the membrane proteins and hydrolases that are required for lysosome function transported from?

A

Trans Golgi Network (TGN)

  • co-translationally transported into rER and then transported via Golgi complex to TGN.
  • TGN buds off into endosomes
  • develop into lysosomes
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15
Q

What is the sorting signal attached to lysosomal hydrolases?

A

mannose-6-phosphate (M6P)

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16
Q

Where is the mannose-6-phosphate (M6P) sorting signal on lysosomal hydrolases attached in?

A

CGN

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17
Q

What recognizes the sugar (M6P) in the TGN?

A

M6P receptors in the TGN recognize sugar.

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18
Q

What two things do receptors bind to in the TGN?

A

Receptors bind to hydrolases and to adaptor proteins in assembling clathrin coats.

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19
Q

What are lysosomal hydrolases packaged into?

A

Clathrin-coated vesicles that bud from TGN.

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20
Q

What causes the dissociation between the lysosomal hydrolase and the M6P receptor?

A

acidic pH inside the early endosome

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21
Q

Once the lysosomal hydrolase and M6P receptor are dissociated in the early endosome, what is removed from the lysosomal hydrolase?

A

phosphate is removed and you now have a lysosomal hydrolase precursor

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22
Q

Once the addition of P-GlcNAc occurs in the cis Golgi network (CGN), what happens to the M6P sorting signal before the protein reaches the TGN?

A

uncovering of M6P sorting signal

so that it can bind to the M6P receptor

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23
Q

What enzyme transfers P-GlcNAc to the mannose in the catalytic site during the assembly of the M6P sorting signal to the lysosomal hydrolase?

A

GlcNAc phosphotransferase

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24
Q

Once the lysosomal hydrolase is released from GlcNAc phosphotransferase, what is removed to complete the addition of the M6P sorting signal?

A

GlcNAc is removed - leaving only M6P bound to the lysosomal hydrolase.

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25
Q

What causes lysosomal storage diseases?

A

Genetic defects in lysosomal hydorlases.

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26
Q

Why do genetic defects in lysosomal hydrolases lead to disease?

A

Accumulation of undigested material in lysosomes.

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27
Q

What enzyme has a mutation that leads to Hurler’s disease?

A

mutation in the enzyme required to break down glycosaminoglycan chains.

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28
Q

What is Inclusion Cell Disease?

A

ALL of the lysosomal hydrolases are missing in many cell types.

  • undigested substrates accumulate as “inclusions”
  • defective or missing GlcNAc phosphotransferase, an enzyme that adds M6P to lysosomal hydrolases.
  • the enzymes are NOT phosphorylated and hence not sorted into vesicles and NOT delivered into lysosomes
  • they are instead carried to cell surface and secreted (found in blood)
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29
Q

What enzyme adds M6P to lysosomal hydrolases?

A

GlcNAc phosphotransferase

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30
Q

What is endocytosis?

A

Uptake of macromolecules from exterior across plasma membrane.

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31
Q

During endocytosis, what type of vesicles ingest large particles?

A

Large particles ingested by vesicles called phagosomes - phaocytosis.

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32
Q

During endocytosis, what type of vesicles ingest small particles?

A

Small particles ingested by pinocytic vesicles - pinocytosis.

33
Q

What is receptor-mediated endocytosis used to do?

A

Import select macromolecules from outside of cell.

  • molecules bind to receptors on membrane surface
  • accumulate in clathrin-coated pits
  • enter cell as receptor-macromolecular complex in clathrin-coated vesicles
34
Q

What does receptor-mediated endocytosis provide?

A

Provides selective concentration mechanism.

  • *example -> cholesterol uptake**
  • *blockage of this pathway results in atherosclerosis**
35
Q

An example of receptor-mediated endocytosis providing a selective concentration mechanism is in the uptake of cholesterol. What would the blockage of this pathway result in?

A

atherosclerosis

36
Q

What are the 3 possible fates of endocytosed receptor proteins?

A

1) recycling of transport vesicles from early endosome
2) transcytosis via transport vesicle
3) degradation in endolysosome

37
Q

Look over storage of plasma membrane proteins in recycling endosomes.

A

Slide 26 - glucose transporters in specialized recycling endosome example.

38
Q

What happens when phagosomes fuse with lysosomes?

A

Ingested material is degraded.

39
Q

What happens to the undigested material in the lysosome?

A

Secreted out by exocytosis.

40
Q

What is phagocytosis triggered by?

A

Binding of particle to receptors on phagocyte surface.

41
Q

What are receptors on phagocyte surface linked to?

A

Functionally linked to cellular response machinery.

42
Q

Describe the mechanism of pahgocytosis using an antibody interaction.

A

> Abs bind to microbe
Fc chain recognized by Fc receptor on surface of macrophage/neutrophil
binding triggers formation of pseudopod which engulfs the particle and forms phagosome
pseudopod formation driven by localized actin polymerization and reorganization
controlled by Rho GTPases and phosphoinositide signaling

43
Q

What does the binding of the Fc chain to the Fc receptor trigger the formation of?

44
Q

What does a pseudopod do?

A

Engulfs the particle and forms a phagosome.

45
Q

What is pseudopod formation driven by?

A

localized actin polymerization and reorganization

46
Q

What is the the pseudopod formation controlled by?

A

> Rho GTPases

> Phosphoinositide signaling

47
Q

What is pinocytosis also referred to as?

A

“cell drinking”

48
Q

Does pinocytosis (cell drinking) occur continuously in all eukaryotic cells?

49
Q

True or False:

Macrophages ingest about 3% of its membrane every minute through pinocytosis.

50
Q

Where does the pinocytosis process begin?

A

At clathrin-coated pits.

51
Q

How many clathrin-coated vesicles leave the plasma membrane of a fibroblast every minute?

52
Q

What are caveolae?

A

Caveolae are flask-shaped invaginations in the plasma membrane.

53
Q

What are caveolae enriched in?

A

Cholesterol and glycosphingolipids, and GPI-anchored membrane proteins.

54
Q

What is the major structural protein in caveolae?

55
Q

True or False:

Caveolae invaginate into membrane by virtue of lipid composition and not the protein coat.

56
Q

What protein pinches caveolae off from the plasma membrane?

57
Q

What do caveolae form after they have pinched off from the plasma membrane?

A

form caveosome (endosome-like compartment)

58
Q

Do caveosome (endosome-like compartments) connect with lysosomes?

A

Do NOT connect with lysosomes.

59
Q

In exocytosis, the transport of vesicles move from _____ to _____.

60
Q

What is the fusion of vesicles with the plasma membrane called?

A

exocytosis

61
Q

Membrane _____ and _____ in transport vesicles from the TGN are destined for the plasma membrane.

A

proteins; lipids

62
Q

What is the regulated secretory pathway in exocytosis triggered by?

63
Q

True or False:

In exocytosis, the constitutive secretory pathway operates continuously.

64
Q

In exocytosis, what type of proteins are secreted out of cells?

A

soluble proteins

65
Q

What are the two different pathways in exocytosis?

A

> constitutive secretory pathway

> regulatory secretory pathway

66
Q

Are newly synthesized plasma membrane lipids transported to the plasma membrane by the regulated secretory pathway or constitutive secretory pathway?

A

Constitutive Secretory Pathway

67
Q

Which exocytosis pathway transports secretory proteins?

A

Regulated Secretory Pathway

68
Q

In the constitutive secretory pathway, is membrane fusion of the newly synthesized soluble proteins for constitutive secretion with the plasma membrane regulated or un-regulated?

A

Unregulated Membrane Fusion

69
Q

In the regulated secretory pathway, does the secretory vesicle storing secretory proteins fuse with the plasma membrane via a regulated or unregulated process?

A

regulated membrane fusion process

70
Q

What are the 3 possible sorting outcomes of proteins in the TGN?

A

1) Signal-mediated diversion to lysosomes (via endosomes).
2) Signal-mediated diversion to secretory vesicles (for regulated secretion).
3) Constitutive Secretory Pathway

71
Q

Proteins destined for secretion are packed into secretory vesicles where?

72
Q

What is selective aggregation/clumping of proteins involved in?

A

Formation of Secretory Vesicles

the mechanism is not fully understood

73
Q

True or False:

Vesicle membrane proteins may have receptors for aggregated proteins or undergo phagocytosis like mechanism.

74
Q

How are proteins concentrated into vesicles during the formation of secretory vesicles?

A

Proteins concentrated into vesicle by RETRIEVAL OF OTHER PROTEINS that go back to TGN and ER.

75
Q

What promotes proteolytic processing of the secretory proteins - activation mechanism - in the formation of secretory vesicles?

76
Q

Notice that on slide 40 what happens to mature secretory vesicle formation as the cargo concentration increases.

A

Notice that retrieval vesicles are clathrin-coated.

77
Q

What are steps in the formation of synaptic vesicles?

A

1) Delivery of synaptic vesicle membrane components to pre-synaptic plasma membrane.
2) Endocytosis of synaptic vesicle membrane components to form new synaptic vesicles directly.
3) Endocytosis of synaptic vesicle membrane components and delivery to endosome.
4) Budding of synaptic vesicle from endosome.
5) Loading of neurotransmitter into synaptic vesicle.
6) Secretion of neurotransmitter by exocytosis in response to an action potential.

78
Q

What are the steps in the exocytosis of synaptic vesicles?

A

1) docking
2) priming I
3) priming II
4) fusion pore opening
5) fusion complete

Molecular Biology - Unit 2 - Zach H. (11 decks)

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