endocytosis Flashcards
whats taken up in endocytosis
-Nutrients
-Signals
-Antibodies
-Enzymes
-Viruses
-Bacteria
-Membrane
what are the different fates of endocytosed material
1)recycling- of proteins
2)transcytosis- exocytosis on the other side of the cell (Apical domain of plasma membrane)
3)degradation -can be taken up by end-some then lysosome
what are the multiple endocytic pathways
-small-scale endocytic process- very small vesicle e.g. clathrin, caveolar, RhoA, flotilla, Cdc42, Arf6
-macropinocytosis
-phagocytosis
-actin provides pulling force for the last two processes
-other pathways exist
what do phagocytes uptake
-large particles
-e.g. Bacteria, apoptotic cells
-Pathogens are often coated by antibodies: opsonization
1) ligand coated particle
2) phagocyte surface receptors (that recognise AB)
3) receptor clusters
4) activation and entry
-mobilisation of actin helps form pseudopods (after stage 3)- allows further engagement of receptor and antibodies
what are Yeast cells taken up by in phagocytosis
-Dictyostelium
whats frustrated phagocytosis
-Fusion of the ruffles is cell autonomous- fusion happens to be within one cell unless it won’t work
-2 phagocytes, 1 bacteria
how can we tell that membrane recycling works
-macrophage phagocytosied 1.1 um latex beads
-by cutting the beads it was possible to estimate how much membrane was internalised
-result: 30% total SA internalised per hour but no change in cell size therefore membrane must be recycled as rate of new membrane synthesis wouldn’t be possible
why is membrane recycling important
-important for cellular homeostasis- difficult without energy
what does macropinocytosis allow
-allows cells to take up lots of volume
-found in a lot of immune cells
-low SA:volume
-lots of fluid taken up from internal environment
-mechanistically similar to phagocytosis
what does Macropinocytosis consist of
-Cells form actin driven ruffles which sometimes fuse to form macropinosomes
-Mechanistically similar to phagocytosis
-Non selective uptake of extracellular material
-Used by cancer cells to take up nutrients
whats Clathrin-mediated endocytosis: hypercholestrolemia
-clathrin coat is easily visible in electron microscope
-LDL transports cholesterol
-cholesterol synthesis LDL receptors- transmembrane receptors embedded in membrane
-they have high affinity for LDL in circulation
-When the receptors are bound to LDL, they clustered together
-when they cluster, they go into these specialised areas of the cell surface and that’s a clathrin coated pit
-for the vesicle to fuse with the early endosome
and the with the relevant snares, it needs to lose the coat so the coat dissociates.
-endocytic vesicle, once uncoated will fuse with the endosome
-In the early endosome it will dissociate the receptor and the LDL come apart.
-the LDL gets targeted ultimately to the lysosome.
-And it releases cholesterol, which is used in the membranes of the cell, and the receptor is sorted and packaged into another vesicle, a recycling reusable, which takes it back to the cell surface.
-efficient way for cells to take up nutrients, because they don’t have to keep synthesising the receptor they’re taking.
whats hypercholestrolemia
-Mutations in LDL receptors: defective binding of LDL or defective internalisation
whats does Clathrin triskelia polymerise into lattices
-heavy and light chain
- 3 chains
-triskelion three legged shape
what happens when there is a mutation in dynamin
-neuromuscular junction Cathrin coated vesicle blocked
-pinching off of protein needed- protein dynamin needed
why is the Gradient of pH key for function on the endocytic pathway
-cells delivered to a late endosomal compartment
-gradient of pH from cell surface to lysosome (low pH)- important for function of endocytic pathway
-viruses that need to be endocytosed , with pH of endocytic compartment used to fuse with cell membrane
-RAB protein- found in particular compartments on endocytic membrane
-pH needs to be 6.5 normally
