L11 - inter-membrane contact sites Flashcards
what are membrane contact sites? (MCS)
close appositions between 2 organelles
Are there membrane contact sites between the endoplasmic reticulum and the mitochondria?
- yes
- ER holds the mitochondria like a hand - membrane become very close but do not fuse
What does the small lipid anchor have to do with MCS?
- lipid is embedded into the membrane which allows organelles to have affinity/bind to organelles which they are making contact with
How can protien tethers (lipid anchors) and bridges be seen between MCS?
- by electon microscopy
Give some of the functions of MCS?
-provide a membrane platform for
- signalling
- non-vesicular lipid exchange
- mobilization of calcium stores
what organelle is the major calcium store of cells?
ER is major calcium store of cells
- close bringing together of calcium stores via intermembrane contact sites
give the major adaptor protein in mammalian cells
AP2
adaptor protein 2
Give the fundamental mechanisms of (clathrin dependent) endocytosis
- 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
what do rab proteins do?
- key in sorting of the early endosome
what rab proteins are abundant on early endosomes?
rab 4
rab5
give some clathrin - independent endocytic pathways
- non-coated vesicles
- calveolae
- macropinocytosis
- phagocytosis
what are calveolae?
- cup shaped invagination of membranes
- invaginations form rosettes in muscle cells - store
- rosettes are endocytotic - take up cargo
what happens in macropinocytosis?
- 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
what does phagocytosis take up?
debris and pathogens
what does clathrin dependent endocytosis take up?
- nutrience
- signalling receptors