Receptor Mediated Endocytosis Flashcards
What maintains cell membrane length so that it does not become ruffled?
Cell membrane length is maintained by the balance between exo and endocytosis.
What is pinocytosis?
This is invagination of the plasma membrane to take up Extracellular solutes.
What drives the invagination of plasma membrane in receptor mediated endocytosis?
Cathrin coat formation on the plasma membrane.
After invagination of the membrane to form a vesicle, what happens next in receptor mediated endocytosis?
There is removal of the clathrin coat by ATP- dependant uncoating protein.
What makes up the clathrin coat?
Clathrin triskeletons which have 3 heavy and 3 light chains.
Where on the plasma membrane are LDL receptors usually found? In what circumstances are they not found here?
LDL receptors are usually found in clathrin coated pits on the plasma membrane. Genetic mutation can mean that this is no longer the case.
How is Cholestrol taken into cells?
Receptor mediated endocytosis.
What two problems with LDL receptors can lead to hypercholestrolaemia?
There can be a non-functional receptor and there can also be a normal receptor but a problem with internalisation and linkage of the receptor to the clathrin coat.
Describe the process of receptor mediated endocytosis.
The molecules are taken into the vesicles still attached to their cell surface receptors and then a pump in the endosome membrane pumps in H+ ions making it more acidic. This results in the ligand uncoupling from the receptor.
What happens to the ligand and receptor at the end of receptor mediated endocytosis of LDL?
The ligand is degraded and the receptor is bound to the cell surface.
In the uptake of Fe3+, what happens to the ligand and receptor?
The ligand (transferrin) is recycled back to the plasma membrane along with the receptor.
What pump is responsible for H+ influx into th endosome in receptor mediated endocytosis?
H+-ATPase
What happens in receptor mediated endocytosis after iron has been released into the cytoplasm?
Apotransferrin remains bound to the receptor and the whole vesicle is exocytosed. Outside of the cell, pH is around 7 and at this pH the ligand dissociates from the receptor.
What is the fate of the ligand and receptor in insulin endocytosis?
Both the ligand and the receptor are degraded.
What is different about the endocytosis of immunoglobulin compared to iron and LDL?
Increase in pH cannot lead to dissociation from receptor. Instead IgA is released by proteolytic cleavage in the bile caniculi. Both the ligand and the receptor are transported.
