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Advanced Cell Biology > Lecture 19 Endocytosis > Flashcards

Lecture 19 Endocytosis Flashcards

1
Q

Transport into the cell requires

A

Cytosolic vesicles

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2
Q

Cytosolic vesicles are

A

Single membrane bound

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3
Q

Trafficking of vesicles involves

A

Budding, scisson, fusion

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4
Q

Vesicles are linked to the

A

ER nd Golgi membranes
Lysosomes
Peroxisomes

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5
Q

3 categories of endocytosis

A

Pinocytosis
Phagocytosis
Receptor mediated endocytosis

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6
Q

Pinocytosis

A

‘Cell drinking’
Unspecific, continuous budding of vesicles from the membrane
Micropinocytosis (>0.1um) or macropinocytosis (0.5-5um)

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7
Q

Pinocytosis is the process by which cells

A

Take up fluids and solutes

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8
Q

Phagocytosis

A

‘Cell eating’
Occurs in specialized cells (macrophages, neutrophils, dendritic cells)
Receptors involved
Used also for clearance of apoptotic bodies

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9
Q

Phagocytosis is the process by which cells

A

Engulf solid matter

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10
Q

Receptor mediated endocytosis

A

Generates small vesicles 60-120nm through invagination
Forms clathrin coated vesicles
Vesicles called endosomes
Can be utilized by viruses

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11
Q

Receptor mediated endocytosis is the process by which cells

A

Absorb metabolites, hormones and proteins (and in some cases viruses)

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12
Q

Endocytosis can be

A

Clathrin dependent or clathrin independent

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13
Q

Clathrin mediated endocytosis stages

A
  1. Initiation - clathrin coat recruited to the bud
  2. Assembly - dynamin recruited to the neck deforms membrane
    (Dynamin is GTPase forms rings in the neck of the budding vesicle)
  3. Dynamin recruits phosphatase to endocytic site
  4. PIP2 creates phase segregation
  5. PIP hydrolysis squeezes the neck, resulting in curvature and finally scisson
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14
Q

Clathrin structure

A

Triskelion shaped scaffold protein

Three heavy and three light chains

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15
Q

Initiation of the clathrin complex requires

A

PIP2 and adaptor proteins

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16
Q

Adaptor proteins link

A

The activated receptors to clathrin

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17
Q

Clathrins act as a

A

Mould so the vesicle forms without direct association of the membrane

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18
Q

Clathrin is a protein which forms

A

A coat around the vesicle

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19
Q

Adaptor proteins

A

AP1-4

Tetrameric adaptor complexes

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20
Q

AP2 is required for

A

CME

clathrin mediated endocytosis

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21
Q

AP2 sits

A

Between activated receptor and the clathrin coat

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22
Q

Clathrin cage disassembly

A

Dissociation rapidly follows scisson of the vesicle from the membrane
Auxilin binds to the triskelion and recruits 3Hsc70:ATP and hydrolyses to 3Hsc:ADP
This energy is used to disassemble the cage

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23
Q

Caveolin mediated endocytosis is

A

Clathrin independent
Membrane deformation is driven by Caveolin and associated Cavin proteins
50-100nm size

24
Q

Cav1-3

A

Caveolin homologues

25
Caveolin mediated endocytosis requires
GTPase dynamin for vesicle scisson
26
Each caveolae contains
150 Cav molecules
27
Caveolin are well described for
Virus internalization
28
After endocytosis vesicles fuse with the
Early endosome
29
The early endosome collects cargo and distributes it to a
Recycling endosome or towards the late endosome for degradation
30
pH of early endosomes
6
31
RabGTPases can be used to identify
Individual endosomes
32
Rab4/11 marks
Recycling endosomes
33
Rab7 marks
Late endosomes
34
Rab proteins are
GTPases | 70 different kinds
35
Rabs are anchored to the membrane by a
Lipid group 'tail' | Prenylation
36
In the inactive state, Rab proteins are
GDP bound
37
In the active state, Rab proteins are
GTP bound
38
The conversion from active to inactive Rab is regulated by
GAPs | GTPase activating proteins
39
The conversion from inactive to active Rab is regulated by
GEFs | Guanine nucleotide exchange factors
40
Prenylation
The addition of hydrophobic molecules to a protein or chemical compound
41
Rab proteins occupy distinct
Membrane domains on endosomes called Rab domains
42
Rab GTPases allow the sequential transport of
Cargo between Rab domains | Rab5 EE -> Rab4 RE-> Rab7 LE
43
Rather than transport
Maturation of endosomes
44
The recycling endosome
Rab4/11 Rab4 = fast recycling Rab11 = slow recycling Rab11 can be seen as a storage endosome
45
Late endosomes/MVBs
Contain membrane bound intraluminal vesicles | Vesicles form by budding into the lumen (ESCRT)
46
The pH of LE/MVB
5-6
47
MVBs can fuse with
Lysosomes for degradation of content
48
MVBs can fuse with the plasma
Membrane to release vesicles for exocytosis
49
Lysosomes
'Lyse' cut/digest pH 4-5 contains hydrolytic enzymes Break down hormones, signalling proteins Released into cytoplasm for re use
50
LDL as an example of RME
Low density lipoproteins LDL binds to LDL receptors on PM Receptor and ligand are internalised into an EE by RME LDL receptor are transported to RE to go back to the membrane LDLs are routed to the LE then lysosome Cholesterol is released to build new membranes
51
Nieman-Pick C disorder (NP)
Mutations in NPC1 gene NPC1 is a cholesterol sensor/binder protein Reduced activity of NPC1 leads to lipid build up in LE and lysosomes Cholesterol gets 'stuck in traffic' Less free cholesterol in the cytosol Affects the trans golgi network (TGN) function and build up in lysosomes eventually kills cells Causes neurological disease, liver spleen and heart
52
Cells internalize substances via
Pinocytosis, phagocytosis or RME
53
Activated receptors interact with adaptor proteins which recruit
A clathrin coat to be internalised in clathrin coated vesicles
54
Vesicle scisson is achieved by
Dynamin and PIP2
55
Vesicles need to be dismantled before interacting with
EE
56
Vesicles fuse with EE to distribute the content to
RE or LE/lysosomes
57
The endocytic cycle is important as it allows the cell to
Receive nutrition and regulate signalling

Advanced Cell Biology (31 decks)

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