Lect1: endocytosis Flashcards
Clathrin mediated endocytosis: - describe:
- describe:
External ligand binds to cell membrane receptor
Internal Clathrin binds internally to the cell membrane receptor, mediates vesicle formation
Vesicle goes to early endosome, later sorted to go into late endosome/lysosome or be recycled
Scatchard Equation:
Looks like the michaelis menton plot. Made by associating how much ligand is binded to your receptor, as you gradually increase the receptor amount. X = ligand conc. NS = % non specific (not your receptor mediated, binding to membrane). Kd dissoassociation constant (related to binding constant?) and Bmax is the maximal amount of binding.
Endocytosis:
- Constituitive:
- Ligand dependent:
- Constituitive:
Receptor will be moved back and forth between interior and exterior of the cell independent of ligand concentration.
- Ligand dependent:
Receptors will be on the outside the cell (predominately) in the absence of ligand, and come into the cell when exposed to the ligand.
YxxΦ motif. Explain
- What is another motif like it
Φ is any hydrophobic residue. Y is tyrosine.
This residue iternally located is necessary and sufficient for clathrin nucleation. It is the binding site of AP2 (Clathrin binds to AP2).
- What is another motif like it?
The FxNPxY domain
CCP (Clathrin Coated pit) formation:
Explain the theory.
AP2 binds to PIP 2 (with its alpha and beta chains), this binding is reffered to as the stochastic assemblies. AP2 also binds via mu2 to the membrane receptor (YXXΦ as the target sequence on membrane receptor). Theorized mu2 is stabilized by cargo bound to the receptor. This allows formation of CCP.
Describe entire process of clathrin mediated endocytosis, including dynamin’s role:
Dynamin pitches the neck, allowing cleavage.
Actin pushes the CCP away, helping it seperate from the cell membrane.
It then uncoats, and fuses with endosomes.
- After endocytosis
- Choices:
- Factors involved:
- Choices:
Receptor and ligand recycle
Receptor recycles and ligand is degraded
Receptor and ligand degraded
- Factors involved:
The pH dependence of the ligand receptor interaction
The cytoplasmic domain of the receptor
The aggregation state of the receptor
Ubiquitination and clathrin mediated endocytosis:
Ubiquitination can stimulate endocytotic machinary (clathrin coating) and start endocytosis. Ubiquitination is normally done on receptors with cargo.
Ca2+ dependent trafficking of Lysosomes and repair?
Ca2+ influx due to high external calcium in puctured cell causes lysosomes to merge and try to fix the damage.
How do bacteria use human lysosome pathways?
Example 1:
Bacteria causes Ca2+ influx, lysosomes fuse, thinking their “saving” the membrane. The bacteria can now go into the cell, as no lysosomes can digest it.
Example 2:
Stimulation of lysosomes can cause them to make a acidic environment for bacterio who need low pH.
Phagocytosis:
Engulfs very large structures, membrane reaches around and engulf bacteria or virus. Engulfed vessicles always go to lysosomes.
Caveolae localization and function(s)
- Locations:
- Functions:
- Locations:
Endothelia (vascular, lung)
Adipocytes
Heart and striated muscle
- Functions:
Endocytosis and transcytosis
Signaling
Mechanoprotection
- What are caveolae?
- Further detail on the function of caveolae:
- What are cavaloe?
Lipid rafts, which often have proteins known as cavins
- Further detail on the function of caveolae:
Endocytosis and transcytosis:
Signaling:
caveolae can also break off and act as transcription factors in the nucleus.
(keeps important signalling proteins like G-protein coupled receptors together and possibly next to their downstream effectors
Mechanoprotection:
Complexed with structural actin filament complex
