Endocytosis Flashcards
What is covering the macrophage surface?
Receptors
What are the 3 different types of endocytosis?
- Pinocytosis
- Phagocytosis
- receptor-mediated endocytosis
Pinocytosis spontaneously makes _____
vesicles
Receptor-mediated endocytosis have a protein ____ on membrane whose purpose is to what?
coat, to deform the membrane
What does receptor-mediated endocytosis create in order to engulf vesicle?
A protein coat to engulf vesicle
Which 2 endocytosis mechanisms are specific?
Phagocytosis & receptor-mediated endocytosis
Which endocytosis mechanisms need receptors?
Phagocytosis & receptor-mediated endocytosis
What changes in the cell during phagocytosis?
reorganization of the cytoskeleton
What are the 2 functions of endocytosis?
Bring material into cell
Recycle PM
All cells use what form of endocytosis?
pinocytosis
Pinocytosis is useful for bulk ___ ____
nutrient uptake
During pinocytosis there is no cop protein or reorganization of PM, but what is still needed when vesicle enters cell to guide it in?
motor protein walking on microtubule
What does phagocytosis consume?
large cells like bacteria and dying cells
Phagocytosis is ____ triggered but ____ independent
receptor, clathrin
What happens to the macrophage membrane when it engulfs another cell?
The membrane changes shape (reorganization of cytoskeleton) and starts to form around the cell it is engulfing
What is the first step in phagocytosis?
phagosyte binds to opsonins
What does the phagosome bind to when phagocytosis starts?
opsonins
When receptors on macrophage bind to bacteria, what happens to the membrane?
there is reorganization of the cytoskeleton - actin filaments grow and the membrane spreads around the bacteria until it fuses around the bacteria.
When does a macrophage become a phagosome?
after it engulfs a bacteria
When does a phagosome become a lysosome?
When the pH drops enough or when it fuses with a lysosome
How does the pH lower in a phagosome?
H-pump are constantly pumping out H and it is lowering the pH
What is a primary lysosome?
brand new lysosome, hasn’t fused with anything yet
What is a secondary lysosome?
a lysosome that is or has already digested things
A phagolysosome will become what?
lysosome
What might happen to a phagosome as its degraded?
It could end up with residual body as lipfuscin
How does receptor-mediated endocytosis engulf?
They all bind to LDL. When receptors bind to LDL it triggers binding of COP proteins which deforms the membrane. No changes in actin, COP protein deforms the membrane.
Where do receptors for receptor-mediated cluster?
lipid rafts
In receptor-mediated endocytosis the cargo _____ binds to the cargo _____
protein, receptor
After the receptor binds to the protein in receptor-mediated endocytosis what protein binds next?
adaptin
What does adaptin bind to?
clathrin
What is the purpose of clathrin?
it binds to adaptin and causes deformation in membrane
As soon as the vesicle buds in receptor-mediated endocytosis what happens to the coat?
the clathrin coat disassembles
Rab-GTPase initiates what?
docking of protein to target membrane, allows v-snare to interact with t-snare
What’s the purpose of NSF/SNAP complex?
disassembles v-snare and t-snare so v-snare can be recycled
What is the purpose of coating the membrane in clathrin?
to deform it and allow vesicle to enter cell
What is the function of adaptins?
they control coated vesicle formation in receptor-mediated endocytosis
Adaptins interact directly with ______ sorting signals
cytoplasmic
What is the structure of clathrin?
triskelion
What is a triskelion?
3 polypeptide chains form 3-legged structure
how many triskelions form a lattice around the vesicle?
36
What part of clathrin binds adaptin?
inner layer
Once the cop protein disassembles on vesicle, what is going to interact?
Rab and v-snare and t-snares will interact
What will an endosome become?
lysosome
Vesicles form at trans golgi with M6P tag, what will bind around this receptor and bring it to lysosome
adaptin
the longer an endosome exists, what happens to its pH?
it lowers
Cholesterol is transported in blood as what?
LDL (cholesteryl esters)
What is needed for membrane synthesis?
cholesterol
When a vesicle fuses with endosome, what happens to LDL?
LDL disassociates from LDL-R
As the pH lowers and endosome becomes lysosome, what happens to LDL?
LDL is hydrolysed to free cholesterol, can now e used to make new membranes
What is caveolin?
another type of protein coat that can form, but it’s not well understood
Where do caveolae form?
lipid rafts
Contrast clathrin vs. caveolae
caveolae have spoked-coat morphology
