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BISC 428 > Lecture 25 > Flashcards

Lecture 25 Flashcards

1
Q

What can macromolecules be mechanized for?

A

1) Captured at the plasma membrane
2) Enclosed within a membrane
3) Invaginated into the cell
4) Pinched off from the plasma membrane

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2
Q

What are the cellular used of endocytosis?

A

1) For feeding (nutrients)
2) For defence (eg. to fuse with lysosomes)
3) To maintain homeostasis

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3
Q

What can the endocytosis process be hijacked by?

A

The process can be hijacked by pathogens that also want to get into cells

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4
Q

What are 5 general types of endocytic mechanisms:

A

1) Phagocytosis
2) Macropinocytosis
3) Clathrin-mediate endocytosis (CME)
4) Caveolin-mediated endocytosis
5) Non-clatrhin/non-caveolin endocytosis (Lipid raft, Flotillin, Tetraspanin, etc)

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5
Q

What endocytic mechanisms are in phagocytosis?

A

Phagocytosis

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6
Q

What endocytic mechanisms are in pinocytosis?

A

Macropinocytosis, Clathrin-mediate endocytosis (CME), Caveolin-mediated endocytosis, Non-clatrhin/non-caveolin endocytosis (Lipid raft, Flotillin, Tetraspanin, etc)

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7
Q

What is phagocytosis used for?

A

Usually used to ingest large particles (>0.1um)
Often used by “phagocytes” from the immune system (Macrophages, neutrophils, dendritic cells), but it also used by other phagocytic cells (eg. Sertoli cells in the testis)

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8
Q

What does phagocytosis require?

A

Requires ligand-receptor binding

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9
Q

What can the ligands be?

A

Proteins
Glycoproteins
Carbohydrates
(usually from bacteria or viruses)

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10
Q

What is the mechanism of action for phagocytosis?

A

Uses actin filaments to push cellular protrusions aorund the material to be internalized

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11
Q

What are the 4 key processes of phagocytosis that take place?

A

1) Attachment
2) Engulfment
3) Fusion with lysosomes
4) Degradation

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12
Q

What is “attachment”?

A

Uses a variety of receptors to identify the target to be ingested by the cell (usually bacteria, foreign bodies, dead cells)
In the case of inflammation, ligands are usually carbohydrates or glycoproteins (eg. C3B part of the complement system or antibodies); these are called “opsonins”

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13
Q

What is opsonization?

A

More phagocytosis

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14
Q

What is “engulfment”?

A

The plasma membrane of the cell “zips” around the particle being internalized by triggering the assembly of actin at sites of particle contact.
So much actin is polymerized that it forms a “phagocytic cup” that will eventually completely surround the particle and engulf it

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15
Q

What is “engulfment/fusion with lysosomes”?

A

Once engulfed, the foreign particle will be found in a phagosome (a membrane bound vesicle)
The actin disassembles
The phagosome is moved using microtubule-based molecules motors towards the cell center

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16
Q

What is “degradation”?

A

Lysosomes fuse with the phagosome and form a phagolysosome
Enzymes from the lysosomes (eg. Lytic enzymes) degrade the foreign particle into:
1) Monosaccharides
2) Disaccharides
3) Nucleotides
4) Amino Acids
5) Lipids
The degraded material is often reused to synthesize new macromolecules in the cell or removed from the cell by exocytosis

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17
Q

What is macropinocytosis?

A

The process of engulfing extracellular material by membrane ruffling

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18
Q

Is there a ligand/receptor needed for

A
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19
Q

Is there a ligand/receptor needed for macropinocytosis?

A

No ligand/ receptor interaction required
Once internalized, the macropinocytosis can last for up to 20 minutes
Then membrane components are recycled or degraded by lysosomes
Some bacteria trigger macropinocytosis for their internalization into their host’s cells

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20
Q

What is Dynamin?

A

An assembly of GTPase dumers that form a spiral around the neck of an invaginating vesicle
Dynamin conformationally changes and constricts the neck of the forming pit (in the presence of GTP) to detach the vesicle from the plasma membrane

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21
Q

How does Dynamin do this?

A

The constriction increases the force on the membrane just above where dynamin binds thereby forcing severing of the plasma membrane from the newly formed vesicular membrane

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22
Q

What does caveolar endocytosis use to make caveolae?

A

Caveolar endocytosis uses caveolin to make caveolae

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23
Q

What does “caveolin” mean?

A

Protein

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24
Q

What does “caveolar endocytosis” mean?

A

The process

25
Q

What does “caveolin-based endocytosis” mean?

A

The process

26
Q

What does “cavin” mean?

A

Protein

27
Q

What does “caveola” mean?

A

Structure (singular)

28
Q

What does “caveolae” mean?

A

Structure (pleural)

29
Q

Where is caveolin found?

A

Found in essentially all cells, but highly concentrated in endothelial cells lining blood vessels

30
Q

What is the structure of “caveolae”?

A

~50-80 nm in size
Flask shaped plasma membrane invaginations
“Little caves”

31
Q

What are “caveolae” membrane microdomains enriched with?

A

Membrane microdomains are enriched in cholesterol, but are stabilized by the proteins “caveolin” and “cavin”

32
Q

What are “caveolae” membrane microdomains enriched with?

A

Membrane microdomains are enriched in cholesterol, but are stabilized by the proteins “caveolin” and “cavin”

33
Q

Where is “cavin” found?

A

Only in vertebrates

34
Q

Where is “caveolin” found?

A

In all metazoans

35
Q

What are the 3 family members of Caveolin?

A

Caveolin 1,2,3

36
Q

What 3 separate genes is caveolin encoded by?

A

Cav 1 and 2 expressed in all tissues, but not skeletal muscle
Cav 3 expressed mainly in skeletal muscle

37
Q

What does caveolin do in endocytosis?

A

Inserts a loop into the inner leaflet of the plasma membrane with both the N and C-termini in the cytoplasm
Is immobilized in the plasma membrane and does not diffuse in the membrane
It does not release from the vesicle

38
Q

What does caveolin and cavin do in endocytosis?

A

A single caveola has ~15 molecular of caveolin
Associates 1:1 with cholesterol
Cavin restricts caveolin to caveolae

39
Q

What does cavin do in endocytosis?

A

Cavin is a trimer that forms rope-like structures on the cytoplasmic side of the caveosome (making the striated coat on the surface of the invaginating vesicle)

40
Q

How many members of cavin are there?

A

4 family members (cavin 1-4)
Caveolin1, caveolin2 and cavin 1 forms a complex that is needed for caveolae formation
Then, Cavin1 binds to cavin 2 or 3 (but not both at the same time)

41
Q

How does caveolae dissociate from the plasma membrane?

A

Caveolae dissociate from the plasma membrane using dynamin into 60nm caveolar vesicles
Caveolar vesicles will fuse with each other or with the other endosomes forming “caveosomes”
They will still retain their caveolar coat
Caveosomes will not fuse with lyosomes

42
Q

What do caveosomes do?

A

They act as conduits for movements of molecules to other areas of the plasma membrane
Without cholesterol (or if caveolin is phosphorylated) caveolae flatten and cavin dissociates from the caveolae

43
Q

What are caveolae often associated with?

A

Caveolae are often associated with stress fibers
A lot of caveolin-1 is co-distributed along stress fibers

44
Q

What happens if you depolymerize actin filaments with Cytochalasin-D?

A

If you depolymerize actin filaments with Cytochalasin-D there is a rapid movement of Caveolin-1 spots in cells that end up localizing to the actin clumps formed by the actin depolymerization

45
Q

What does this suggest?

A

This suggests that there is something (a tether) linking caveolae to actin

46
Q

What is the linker called?

A

The linker is Filamin-A

47
Q

What is Filamin-A?

A

An actin cross linker
Directly binds to caveolin-1

48
Q

What happens in a KD Filamin-A?

A

Increased lateral motility of caveolin-1 and decreased co-alignment with stress fibers

49
Q

What is the EH Domain Containing 2 (EDH2)?

A

It is a membrane remodeling protein that is similar to Dynamin

50
Q

What does EDH2 bind to?

A

EDH2 binds to another protein Paosin-2, which binds to actin filaments

51
Q

What happens when you knock down EDH2?

A

Knocking-down EDH2 expression causes more caveloae to move (so their not anchored anymore)

52
Q

How can caveolae shape change?

A

Caveolae are packed with signalling molecular and aren’t only separate, cup-shaped structures
When under osmotic or mechanical stress caveolae can flatten out!

53
Q

What is osmotic swelling involved in?

A

Osmotic swelling is also involved in signaling events coming from caveolae.
Osmotic swelling (this flattening of caveolae) causes caveolin-1 to disengage from the caveolae and move to the cytosol

54
Q

What is a weird shape of caveolae?

A

Rosettes

55
Q

How are rosettes generated?

A

Addition of Cytochalasin-D generates more rosettes

56
Q

What are the advantages of rosette formation?

A

Might provide additional flexibility to membranes under stress

57
Q

What are rosettes used for?

A

Rosettes are also used to endocytose large chunks of membrane

58
Q

When are rosettes formed?

A

Rosettes are formed prior to caveolin-1 endocytosis

59
Q

What does reducing cholesterol do to caveolae shape?

A

Reducing cholesterol also cause caveolae to flatten out but they keep their striations

BISC 428 (23 decks)

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