M&R Session 6 (Lecture 6.2) Flashcards
What is the difference between phagocytosis, pinocytosis and endocytosis?
1) Internalisation of particulate matter
2) Invagination of the plasma membrane to form a vesicle
3) Permits uptake of extracellular solutes
4) Selective internalisation of molecules into the cell by binding to specific cell surface receptors
What do LDLs comprise of?
A core of esterified cholesterol esters
Covered by a phospholipid and cholesterol monlayer
Containing apoprotein B
What are triskelions?
Coat stuctures made up of hexagons and pentagons
Hexagonal and pentagonal structures formed from clathrin triskelions
Triskelions comprise 3 clatrin heavy chains and 3 light chains
How is a clathrin coat formed and uncoated?
1) Clathrin coated pits form spontaneously
2) Uncoated by an ATP-dependent uncoating protein
What are two potential mechanisms of hypercholesterolaemia for the LDL R and clathrin coat?
EITHER
Non functional receptor with normal coated pits
OR
No internalisation
LDL Rs distrubted over whole cell surface
Deletion of C-terminal cytoplasmic domain prevents interaction with the clathrin coat
How is acidification acheived and what is its effects in the LDL R + ligand vesicle?
Proton pump using ATP translocates H+ into the vesicle lowering the pH.
This causes the ligand to dissociate from the receptor in the endosome. The ligand (LDL) is directed to the lysosome and the receptor is recycled.
What is another name for the endosome?
Compartment of Uncoupling of Receptor and Ligand
What is the endocytosis of LDL R + LDL ?
Ligand degraded
Receptor recycled
What is the endocytosis of transferrin + transferrin R?
Ligand recycled
Receptor recycled
What is the endocytosis of insulin R + insulin?
Ligand degraded Receptor degraded (desensitises the cell)
What is the endocytosis of Igs + IgRs?
Ligand transported
Receptor transported
How can the RME pathway be tricked? Describe the process.
Can be used by membrane-enveloped viruses.
1) Binding to cells by fortuitous association with cell receptors.
2) Entering cells via clathrin-coated pits
3) Unfolding hydrophobic domains in membrane fusion proteins in response to the acidic pH of the endosome
4) Inserting membrane fusion proteins into the endosome membrane leading to membrane fusion and to release gRNA into cytoplasm
5) Using host cell machinery to replicate RNA and capsid proteins to bud new viruses at the cell membrane.
Give two examples of toxins that use the RME pathway. What do they bind to?
Cholera and Diptheria toxin bind to GM1 gangliosides.
What are the two other coat proteins along with clathrin? What do they do?
Clathrin - pm coated pits
COP I - E.R
COP II - Golgi apparatus
