L5 - Mechanism of endocytosis and maturation and sorting in the endosomal system Flashcards
(23 cards)
what are the 3 different endocytosis pathways at plasma membrane
- Phagocytosis - uptake of large particles by specialised cells
- Macropinocytosis - soluble molcules uptaken in non-specific manner via captire by membrane
- Pinocytosis - specific + non-specific capture of vesicles
describe phagocytosis simply of a bacteria
- Fc of antibodies bind Fc receptors
- signalling cascade –> actin polymerisation
= extensions ‘wrap’ arouynd and engulf bacteria
what is required in macropinocytosis to cause membrane ruffles
Small GTPases + actin
= Rho-family –> Rac1
describe the proscess of macropinocytosis simply
Non-selective
- formation and protrusion of membrane ruffles
- ruffle folds back in on itself
= vesicles are capture inside lumen of ruffle
what is a triskelion in clathrin coats
cage/lattice structure
3 heavy + 3 light chains of clathrin come to together –> helps distort membrane + drive vesicle formation
describe the a single unit in clathrin coat formation simply - what is bound to what
Cargo receptor in membrane bound to cargo
Adaptor complex - adaptin bound to receptor
clathrin binds to adaptor = forms triskelion
what kindve motion does dynamin move to cause scission of leaving vesicles
twisting motion - is a GTPase
= once vesucle is formed the clathrin detaches allowing recognition of early endocytic compartment
how are high levelss of choletsreol built up in Famila Hypercholesterolemia
mutation in Low-Density-Lioprotein receptor (LDL) in adaptin
= LDL binding is not receognised –> no calthrin coated pit forms for internalisation
Adaptor complex does not bind to receptor –> Clathrin does not bind too adaptor –> no inetrnalisation –> cholesterol build up
name the adaptor clathrin complex that cannot bind to defective LDL receptors in familaila hypercholesterolemia
AP2
what happens to the pH as you move further down the endosomal/lysosomal system
pH drops = more acidic
pH maintained by actively pumping H+ intp compartments
descirbe what happens to cholesterol endocytosed
- low pH causes coat to come off + LDL receptor retuned to membrane from early endosome
- LDL moves into late endosome THEN lysosome
- lysosome contains hydrolytic enzymes that break down protein element of LDL
= release Cholesterol
how is the trasnferrrin/transferrin receptor trafficking from endocytosis different to LDL
transfferin stays bound to receptr until its recycled back to membrane
LDL = receptor released at low pH after coat disociates
what is the endolysosomal system
method of sorting incoming material to prper place to meets cells requirements
end in either:
- recycling/degredation (lysosome)
- biosynthesis (golgi)
how does the endo-lysosomal system deal with sorting decisisions
cytoplasmic signals and pH changes
= we can track specifc proteins by tagging KNOWN proteins and using them as markers
how can we identify what pathway a specific protein is in
pathways are well charecterised
track specifc proteins by tagging KNOWN proteins and using them as markers
= compare ‘target’ against ‘established’ receptors to see where and why thety are sorted
what Rab-GTPase is associated with early endosome
Rab5
what Rab-GTPase is associated with late endosome + lysosome
Rab7
what Rab-GTPase is associated with Golgi/TGN
Rab6§
what have Rab-GTPases been asociated with
different compartmenst + mechanisms
= Rab4 associated with fast recycling FROM the early endosome
there is overalp between certin systems and Rab-GTPases
define endosomal maturation
change from early –> late endosomes + lysosomes
= particularly how they change comnpartment identity by changing Rab-GTPase
how is compartment identitiy changed
changing Rab-GTPase asscociated with
= different Rabs have differnt effectors = organelle functions shift
give an exmaple with RabA and Rabb (not real Rabs) for endosomal maturation and how this can act as a ‘switch’ to shift identity
- RabA activatated by GEF –> effector proteins activated
- one of the effectors COULD be a GEF for ANOTHER Rab-GTPase
- RabB activation –> RabB has its own effectors that are activated
- One effector may be a GAP that inactivates RabA + a GEF that activates RabB more
= organelle functions change and mature
describe the switch with Rab5-7 in early to late endosomal maturation
- Rab5 recruits GEF Mon1 –> activates Rab7
- Active Rab7 recruited and activated –> Rab7 effectors take over
eg: HOPS tethering complex for fusion with lysosomes
