| Term | Definition |
|---|
| peroxisomes | small membrane bound organelles that contain oxidative enzymes, Use molecular oxygen to oxidize organic molecules, Contain some enzymes that produce and others that degrade H2O2, Breakdown of long chain fatty acids, Import of cytosolic proteins |
| catalase (40% of protein) | uses H2O2 generated by other enzymes to oxidize other substrates – phenols, formic acid, formaldehyde, alcoho |
| catalase rxn important bc? | this oxidation reaction is important in liver and kidney cells, where peroxisomes detoxify various toxic molecules |
| Breakdown of long chain fatty acids is another important function of peroxisomes | β oxidation of fatty acids generates acetyl CoA, peroxisomes export acetyl CoA to cytosol |
| Import of proteins into perioxisomes | Import signal is usually a 3 aa motif (SKL) that is recognized by a receptor on perioxisome membrane |
| Zellweger Syndrome | caused by a genetic defect in the protein import process (SKL receptor?) of peroxisomes, as a result of this defect, there are no enzymes in the peroxisomes ("empty peroxisomes") |
| Zellweger Syndrome: lack of peroxisome enzymes causes | a severely abnormal brain, liver, kidneys. affected infants die shortly after birth |
| receptor mediated endocytosis | macromolecules bind to complementary transmembrane receptors in coated pits and then enters cell as recepto-macromolecule complexes in clathrin-coated vesicles |
| coated pits | specialized region coated with clathrin (directs and stabilizes) on cytoplasmic face. Invaginates to form coated vesicles. Then sheds protein coat and fuses with early endosomes |
| clatharin | the protein on the cytoplasmic side of coated pits, has three light and heavy chains. has a form of a three legged structure called a triskelion |
| triskelions | interact to form a basket on the cytoplasmic surface of a membrane that will pinch off to form a membrane vesicle. three legged structures on clatharin protein complex |
| adaptins | protein complex that traps transmembrane proteins (frequently receptors) and also bind clathrin. bind to a motif (four amino acids) present on transmembrane receptors |
| adaptins enrich the number of receptors present in | a coated pit/vesicle and promote uptake of certain ligands |
| different adaptins facilitate the interactions of different proteins | with a forming clathrin coat |
| significance of receptor mediated endocytosis | mechanism allows for selective uptake of a substance at high rate |
| examples of receptor mediated endocytosis: cellular uptake of | LDL (low density lipoprotein), transferrin (iron binding protein), EGF (epidermal growth factor), antibodies in mothers milk, certain hormones, viruses, toxins |
| internalized endocytic vesicle containing ligand-receptor complexes fuses | with an early endosome, many receptors dissociate from their ligand at acidic pH |
| early endosomes have acidic pH and late endosomes have an even more acidic pH | acidic pH is established and maintained by a vacuolar H+ ATPase that pumps H+ into lumen of endosome |
| receptor recycling | receptor is transported back to the plasma membrane in a small vesicle that buds from the endosome. |
| what is the fate of the dissociate ligand | transported to late endosome and lysosome where it is degraded |
| if receptor does not dissociate from its ligand, then | both the receptor and its ligand can be transported to a late endosome and lysosome where the complex is degraded |
| transcystosis | process where the receptor is relocated to a different location within that plasma membrane |
Combine with other sets
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