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Advanced Cell Biology > Lecture 19 Endocytosis > Flashcards

Lecture 19 Endocytosis Flashcards

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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
Q

Caveolin mediated endocytosis requires

A

GTPase dynamin for vesicle scisson

26
Q

Each caveolae contains

A

150 Cav molecules

27
Q

Caveolin are well described for

A

Virus internalization

28
Q

After endocytosis vesicles fuse with the

A

Early endosome

29
Q

The early endosome collects cargo and distributes it to a

A

Recycling endosome or towards the late endosome for degradation

30
Q

pH of early endosomes

A

6

31
Q

RabGTPases can be used to identify

A

Individual endosomes

32
Q

Rab4/11 marks

A

Recycling endosomes

33
Q

Rab7 marks

A

Late endosomes

34
Q

Rab proteins are

A

GTPases

70 different kinds

35
Q

Rabs are anchored to the membrane by a

A

Lipid group ‘tail’

Prenylation

36
Q

In the inactive state, Rab proteins are

A

GDP bound

37
Q

In the active state, Rab proteins are

A

GTP bound

38
Q

The conversion from active to inactive Rab is regulated by

A

GAPs

GTPase activating proteins

39
Q

The conversion from inactive to active Rab is regulated by

A

GEFs

Guanine nucleotide exchange factors

40
Q

Prenylation

A

The addition of hydrophobic molecules to a protein or chemical compound

41
Q

Rab proteins occupy distinct

A

Membrane domains on endosomes called Rab domains

42
Q

Rab GTPases allow the sequential transport of

A

Cargo between Rab domains

Rab5 EE -> Rab4 RE-> Rab7 LE

43
Q

Rather than transport

A

Maturation of endosomes

44
Q

The recycling endosome

A

Rab4/11
Rab4 = fast recycling
Rab11 = slow recycling
Rab11 can be seen as a storage endosome

45
Q

Late endosomes/MVBs

A

Contain membrane bound intraluminal vesicles

Vesicles form by budding into the lumen (ESCRT)

46
Q

The pH of LE/MVB

A

5-6

47
Q

MVBs can fuse with

A

Lysosomes for degradation of content

48
Q

MVBs can fuse with the plasma

A

Membrane to release vesicles for exocytosis

49
Q

Lysosomes

A

‘Lyse’ cut/digest
pH 4-5 contains hydrolytic enzymes
Break down hormones, signalling proteins
Released into cytoplasm for re use

50
Q

LDL as an example of RME

A

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
Q

Nieman-Pick C disorder (NP)

A

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
Q

Cells internalize substances via

A

Pinocytosis, phagocytosis or RME

53
Q

Activated receptors interact with adaptor proteins which recruit

A

A clathrin coat to be internalised in clathrin coated vesicles

54
Q

Vesicle scisson is achieved by

A

Dynamin and PIP2

55
Q

Vesicles need to be dismantled before interacting with

A

EE

56
Q

Vesicles fuse with EE to distribute the content to

A

RE or LE/lysosomes

57
Q

The endocytic cycle is important as it allows the cell to

A

Receive nutrition and regulate signalling

Advanced Cell Biology (31 decks)

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