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21 Cards in this Set
- Front
- Back
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what are macrophages? |
eating cells. They take up 25% of their mass every hour they eat invading bacteria, dead cells, etc |
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what are the 2 ways of receptor mediated endocytosis? |
1. Clathrin mediated 2. Calvaeolae mediated |
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How does clathrin mediated endocytosis work? |
1. Receptors are in clathrin-coated pits 2. Ligands bind 3. Pit pinches off 4. Clathrin coating leaves 5. fuses with a larger vesicle, becomes "endosome" 6. pH change, causes ligand to unbind 7. receptors sequester to one side 8. receptors bud off 9. ligands now go wherever they're needed |
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how was clathrin discovered? |
Barbara Pierce: stripped off coat, ran western blot, found that there are 3 light chains and 3 heavy chains; there's a "triskelion" shape |
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what's an example of a receptor that moves into the pit only after binding? |
Insulin: it only moves to the pit once it's bound |
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How was Dynamin Discovered? |
It was discovered through the shibire fly mutant, which becomes paralyzed at a high temperature |
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What was discovered at 30*C shibire fly tissue? |
1. Nerve cells had no synaptic vesicles 2. other cell types had no coated vesicles, but LOTS of coated pits and excess membranes |
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What does dynamin do? |
It pinches off the vesicles during endocytosis |
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why does mutant dynamin not work? |
It can't cleave GTP when mutant, which is how it is able to pinch off the pit |
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What is the uncoating atpase and how was it discovered? |
Dr. Schmid fractionated the cytoplasm and tested each fraction for uncoating activity; discovered hsc70 |
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how do some endosomes and other organelles have acidic ph? |
There's a proton pump that pumps in... protons |
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what is the most famous endocytosis receptor and what does it do? |
It's the LDL Receptor (low density lipoprotein) - ligand binding domain - 350 amino acids > Beta propeller - sugar residue - transmembrane - short tail Every LDL receptor is used for 100 there-and-back trips |
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What happens if you delete LDL transmembrane region? |
LDL receptors are secreted, but LDL particles not endocytosized |
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LDL sugar region deleted? |
no change |
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Ligand binding domain deleted? |
ligands can't bind, LDL particles not endocytosized |
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Cytoplasmic tail deleted? |
LDL not found in pits! |
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Delete STAR 350 aa part of LDL? |
Ligand binds, LDL endocytosized, but will not release ligands at acid PH |
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What does LDL star region do? |
Needed for conformational change at acid pH |
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How does an acid pH affect Beta propeller? |
Surface of B propeller becomes positively charged then binds to the ligand binding arm, freeing the ligand |
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What happens if the ligand does not unbind LDL? |
It goes on with the ligand and is eventually degraded, therefore only being used once.
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what happens in transcytosis? |
when antibodies bind to receptors in lumen that then take them to the other side of the cell and release outside |
