M&R Session 6- Principles Of Receptor- Mediated Endocytosis Flashcards
What mechanism is used in phagocytosis?
Membrane zippering.
Define phagocytosis
The internalisation of particulate matter.
What is pinocytosis?
The internalisation of plasma membrane to form a vesicle.
What does pinocytosis allow the uptake of?
Extracellular solutes
What is endocytosis?
The selective internalisation of molecules by binding to specific cell surface receptors.
What does cholesterol have to be packaged in?
LDLs
Describe the components of an LDL
Core- esterified cholesterol esters
Lipid monolayer- phospholipids, cholesterol and apoB
In cholesterol RME, where are LDL receptors clustered?
Over coated pits
What happens to the coated pits
They invaginate and pinch off from the plasma membrane to form coated vesicles
What happens to the coated vesicles?
They are quickly uncoated
What happens to the uncoated vesicles?
They bind with larger smooth vesicles called endosomes
What pH is the endosome maintained at?
What maintains it?
5.5-6
ATP- dependent proton pump
What happens due to the pH of the endosome?
The LDL receptor has low affinity for the LDL so they dissociate
What is the endosome known as?
Compartment for Uncoupling of Receptor and Ligand (CURL)
What happens to the receptor and LDLs in the endosome after dissociation? (2)
The LDL receptors bud off in a vesicle and are returned to the plasma membrane.
The LDLs are budded of in a vesicle and fused with the lysosome so that the cholesterol can be hydrolysed from the esters and released into the cell.
What are coat structures called and made up of?
Triskeletons
Clathrin and two light chains
Do clathrin coated pits from spontaneously?
Yes
What uncoates clathrin coated vesicles?
ATP dependent in coating protein
What happens to the ligand and receptor in cholesterol RME?
Ligand- degraded
Receptor- recycled
Describe RME of Fe3+ ions
- 2 Fe3+ ions bind to apotransferrin to form transferrin
- transferrin binds to transferrin receptor on coated pit and is internalised as cholesterol example.
- Fe3+ ions are released at acidic endosome, leaving apotransferrin attached to receptor.
- apotransferrin-receptor complex is recycled to plasma membrane and dissociate as neutral pH again.
What happens to the ligand and receptor in Fe3+ RME?
Ligand- recycled
Receptor- recycled
What is the fate of the ligand and receptor in insulin RME?
Both are degraded
What does the insulin mechanism allow for?
Reduction in number of insulin receptors at cell surface- down regulation
What is the fate of the ligand and receptor in transcytosis of immunoglobulin?
Ligand and receptor are transported
How do membrane-enveloped viruses and toxins exploit endocytic pathways?
They bind to receptors on plasma membrane, and once in the endosome, they fuse with the endosomal membrane and release their RNA into the cell which can be translated to give more viral particles.
