L11 - inter-membrane contact sites Flashcards

1
Q

what are membrane contact sites? (MCS)

A

close appositions between 2 organelles

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2
Q

Are there membrane contact sites between the endoplasmic reticulum and the mitochondria?

A
  • yes

- ER holds the mitochondria like a hand - membrane become very close but do not fuse

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3
Q

What does the small lipid anchor have to do with MCS?

A
  • lipid is embedded into the membrane which allows organelles to have affinity/bind to organelles which they are making contact with
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4
Q

How can protien tethers (lipid anchors) and bridges be seen between MCS?

A
  • by electon microscopy
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5
Q

Give some of the functions of MCS?

A

-provide a membrane platform for

  • signalling
  • non-vesicular lipid exchange
  • mobilization of calcium stores
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6
Q

what organelle is the major calcium store of cells?

A

ER is major calcium store of cells

- close bringing together of calcium stores via intermembrane contact sites

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7
Q

give the major adaptor protein in mammalian cells

A

AP2

adaptor protein 2

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8
Q

Give the fundamental mechanisms of (clathrin dependent) endocytosis

A
  • ligand binds to transmembrane receptor
  • ligand-receptor complexes become clustered in clathrin coated pits
  • adaptor protein acts as a link between cargo in the vesicle and vesicle coat (clathrin)
  • membrane pinched off by dynamin and early endosome forms containing cargo
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9
Q

what do rab proteins do?

A
  • key in sorting of the early endosome
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10
Q

what rab proteins are abundant on early endosomes?

A

rab 4

rab5

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11
Q

give some clathrin - independent endocytic pathways

A
  • non-coated vesicles
  • calveolae
  • macropinocytosis
  • phagocytosis
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12
Q

what are calveolae?

A
  • cup shaped invagination of membranes
  • invaginations form rosettes in muscle cells - store
  • rosettes are endocytotic - take up cargo
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13
Q

what happens in macropinocytosis?

A
  • non-selective form of endocytosis where cells take up the EC environment
  • immune cells use this to sample environment they are in

-mobilizaiton of actin forms a pseudopod which can take up EC en. - cells ruffle

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14
Q

what does phagocytosis take up?

A

debris and pathogens

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15
Q

what does clathrin dependent endocytosis take up?

A
  • nutrience

- signalling receptors

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16
Q

How many subunits do adaptor proteins have?

A
  • 4 subunits
17
Q

which adaptor protein subunit does clathrin bind to?

A

Beta subunit of adaptor proteins

18
Q

which adaptor proteins bind to clathrin?

A

AP1 (trans-golgi-network)

AP2 (plasma membane)

19
Q

how many adaptor proteins are there?

A

AP1-5

20
Q

where is AP5 found?

A

adaptor protein found on late endosomes (still require sorting)

21
Q

which subunit of adaptor proteins recognises sorting signals?

A

Mu (μ)

- cargo binding so recognises sorting signals on cargo

22
Q

what is co-incidence detection?

A
  • where adaptor proteins bind to cargo and bind to phosphoinositides
    (both are required which allows co-localisaiton of adaptor proteins)
    -needed as mu subunits recognise similar signals and same cargo/sorting signal may be present in multiple locations.
23
Q

what phosphoinositides do AP1 and AP2 bind to?

A
  • AP1 binds to cargo and PI4P

- AP2 binds cargo and to PI(4,5)P2

24
Q

what helps to define the endocytotic intermediates?

A

rabs and phosphoinositides

different PIs at different places in the cell- lable with GFP to visualise localisations

25
Q

what are CLASPs?

A

clathrin associated sorting proteins

26
Q

what are the recognition motifs on Adaptor proteins?

A

WxxF and DP[FW]

27
Q

what is the dynamin homolgue in drosophila?

A

shibre
(GTPase - riquired for pinching off of clathrin coated vesicles)
- accumulation of endocytotic intermediates if dynamin cannot function (at high temperatures)

28
Q

what removes the clathrin coat?

A

hsc70

-clathrin coat needs to be removed to fuse with endosomes