Endomembrane System II Flashcards
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protein export out of the rough ER and into the golgi
protein export out of the golgi and into the plasma membrane
Cop II vesicle
a protein coat complex that transports protein out of the rough ER into the golgi
Cop I vesicle
a protein coat complex that transports proteins from the cis golgi back to the rough ER.
KDEL sequence
ER retrieval signal present in mammals and plants
ER lumen proteins
golgi —> rough ER lumen
Cytoplasmic tails with arginine or lysine
ER retrieval signal resident transmembrane rough ER proteins
golgi –> rough ER
ER retrieval signals (2)
KDEL sequence
Cytoplasmic tails with arginine or lysine
What does ER retrieval signal mean?
(retrives from golgi and sends back to ER)
Necessary signal
signal is necessary for protein to remain in ER; if it’s deleted it will be secreted
Sufficient signal
signal transplanted to secreted protein and it will then remain in the ER
‘bulk flow’
default transport of ER resident proteins out of the ER and to the golgi
How are KDEL-receptors returned to the cis-golgi?
At rough ER pH is less acidic, favouring unbinding of KDEL-signal and KDEL-receptor. KDEL receptor packaged into COP II vesicle.
What does golgi residency/retention signal mean?
retrieves from plasma membrane and sends back to golgi
Whis is the golgi residency/retention signal?
TMD 17-20AA in length which is specific to golgi membrane thickness.
Short cytoplasmic tails
LDL Particles
transport cholesterol to cells
What is the golgi residency/retention signal?
TMD 17-20AA in length which is specific to golgi membrane thickness.
Short cytoplasmic tails
Two protein layers of Clathrin Coated Complex
Clathrin complex (outer layer) Adaptin complex (inner layer)
Clathrin coated pits
patches of plasma membrane that concentrate receptor molecules and curve to form an invagination that buds off in endocytosis with receptor cargo inside the vesicle.
How is cholersterol taken up by the cell?
- cholesterol is transported in LDL particles which bind to an LDL receptor at the plasma membrane
- Cholesterol is enocytosed via formation of a Clathrin Coated vesicle
How do CCVs select cargo?
Adaptin 2 interacts with teh cytosolic tail of the receptor molecule that is holding teh cargo
How do CCVs select cargo at specifically the plasma membrane?
Adaptin 2 interacts with the cytosolic tail of the receptor molecule that is holding the cargo
FHC (Familial hypercholesterolaemia)
mutations in cytosolic tail/patients lack LDL receptor meaning CCVs cannot form and so cholersteral cannot be endocytosed, leading to heart disease since it isn’t taken up from the blood stream.
Where are CCVs which have entered through the PM targeted to?
early endosome
What happens to CCVs at the early endosomes?
Receptor and cargo dissociate
Receptors (in this case LDL receptors), are returned to the plasma membrane via the recycling endosome
Cargo travels to the late endosome and is mixed with lysosome proteins arriving from the golgi in the secretory patwhay. Both continue to the lysosome.
Lysosomal Hydrolases are transported from
trans-golgi to late endosome
Early endosome pH
6-6.5 lower than cytosolic pHso causes receptor and cargo to dissociate
Where are lysosome hydrolyases made?
the rough ER
What do enzymes of the cis-golgi do to lysosomal hydroloases?
Kinase phosphorylates a specific mannose residue on the N-glycan which creates a Mannose-6-phosphate signal
How do enzymes of the cis-golgi recognise lysosomal hydroloases?
recognise a ‘signal patch’ in their tertiary structure
Mannose-6-phosphate receptor
In trans-golgi and binds to the mannose-6-phosphate signal on the lysosomal hydrolase.
When lysosomal hydrolases are transported from the trans-golgi to the late endosome, what are they transported in?
Clathrin Coated Vesicle
How do CCVs select cargo at specifically the trans-golgi?
Adaptin 1 interacts with the Man-6P receptor
