Receptor Mediated Endocytosis (6) Flashcards
What are the three main membrane internalisation methods?
- Phagocytosis: internalisation of particulate matter
- Pinocytosis: invagination of plasma membrane to form a vesicle
permits uptake of extracellular salutes - Endocytosis: selective internalisation of molecules into cell by binding to specific cell surface receptors
What is meant by vascular transport?
- Membrane vesicles bud from donor organelle and are transported to destination where they fuse with recipient organelle
What does REM stand for and give an example?
- Receptor mediated endocytosis
- Uptake of cholesterol
How do clathrin vesicles form and how are they disassembled?
- Clathrin coated pits form spontaneously and bud off to form vesicles
- Clathrin coated vesicles are uncoated by an ATP dependent uncoating protein
- Clathrin triskelions are recycled back to for new clathrin coated pits
What are the mutations affecting LDL receptors in hypercholesterolaemia?
- Normally binding receptor: no binding of LDL but still normal coated pits and internalisation
- Non functioning receptor: no internalisation, LDL receptors found distributed over whole cell surface, deletion of C-terminal cytoplasmic domain prevents interaction with clathrin coat.
Outline the receptor mediated endocytosis of LDLs and where do they end up?
- LDL moves into coated pit randomly
- Coated pit buds off to form coated vesicle (clathin cage formation)
- Uncoating of vesicle by ATP dependent uncoating protein
- Enters endosome
- Either moves to Golgi or lysosome
How does CURL happen in the endoscope?
- Compartment of uncoupling of receptor and ligand
- pH change due to high H+ concentration in endosome uncouples the receptor and ligand
After the LDL is processed in the endosome what are the possible options next?
- Ligand degraded
- Receptor recycled
How does ligand recycling occur?
- use transferrin as an example
- Apotransferrin taken in
- Ferrin is unloaded into endosome
- Apotransferrin remains bound in endosome so is released when endosome is recycled and exocytosed
- pH decrease doesn’t cause decrease in affinity
How does transcytosis occur?
- From endosome to transfer vesicle
- NOT discharged in CURL
- Transfer vesicle has antibodies bound
- Moved to the bile where all contents are degraded
- Ligand and receptor are degraded.
Outline the process by which membrane enveloped viruses are endocytosed.
- Binds to cells by fortuitous association with cell receptors
- Entering cells via clathrin-coated pits (RME)
- Unfolding of hydrophobic domains in membrane, fusion proteins in response to acidic pH of endosome
- Inserting membrane fusion proteins into the endosome membrane leading to membrane fusion and release genomic RNA into cell cytoplasm
- Using host cell machinery to replicate RNA and capsid proteins -> new viruses at cell membrane.
Give two examples of toxins entering by receptor mediated endocytes
- Cholera
- Diptheria
Give three examples of coat proteins.
- Clathrin - plasma membrane coated pits
- COPI - ER
- COPII - Golgi
