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Secretion
UCI SOM Liu
| Question | Answer |
|---|---|
| Cytosolic ribosomal polypeptides can end up where | cytosol, mitochondrion, peroxisome, and nucleus |
| Rough ER polypeptides can go where | ER, golgi, secretory vesicles, plasma membrane, endosome, and lysosome |
| Which membranes use membrane translocation for protein transport | mitochondrion, peroxisome and ER |
| How do proteins get inside the nucleus | gated transport |
| How do proteins transport into the golgi, secretory vesicles, plasma membrane, endosomes, and lysosomes | vesicular transport |
| Where are proteins glycosylated | ER and golgi |
| In which cell locations are proteins not glycosylated | cytosol, mitochondrion, peroxisome, and nucleus |
| Proteins destined to mitochondria have what | amino terminal leader sequence (lots of positive charged AA’s |
| Is translocation into the mitochondria co-translational | no |
| What’s different about mitochondrial protein translocation | protein is unfolded |
| Pre- sequence | signal peptide on nearly all secreted peptides |
| 6 signal sequence features | 1)on N-terminus 2)12-35 AA long 3)Met is first AA 4)central group of hydrophobic AA 5)at least one + charged AA near N-terminus 6)cleaved off at Ala by signal peptidase |
| what halts translation in ER bound proteins | SRP |
| SRP features | 6 polypeptides, 7S RNA; the 54k subunit contains 12% methionine to bind the hydrophobic signal peptides |
| When is the SRP-imposed block released | after docking to the ER on the SRP receptor |
| When is the signal peptide cleaved off in the ER | once ER translocation is complete |
| When is the protein glycosylated in the ER | immediately |
| What kind of signal does an integral membrane protein have | an internal halt- or stop- transfer signal. |
| Where is the glycosylated part of a protein NEVER located | in the cytoplasm |
| Glycoproteins are suggested to contribute to what | metastasis of cancers |
| 3 classes of glycoproteins | O-linked, N-linked, GPI-anchored |
| o-linked linkage | GalNAc-Ser/Thr |
| n-linked linkage | GlcNAc-Asn |
| GPI-anchored linkage | oligosaccharide which is linked to the protein at the C-terminus with phosphorylethanolamine and is also linked to a phosphatidylinositol (PI) |
| 3 classes of o-glycosidic linkages | 1)GalNAc-Ser/Thr; most common (mucin) 2)proteoglycans contain Gal-Gal-Xyl-Ser/Thr then long repeating disaccharides (synovial fluid) 3)Collagen contains Gal-hydroxylysine |
| where does addition of sugar residues occur in o-glycosylation and when does it occur | occurs in the ER and is cotranslational. |
| Three classes of N-linked glycoproteins | complex, hybrid, and high-mannose |
| Common N-linked structures | Asn-2GlcNAc-3Man |
| When and where are N-linked glycoproteins glycosylated | in the ER wherever Asn-X-Thr/Ser occurs (X is any AA except Pro) |
| Where does the oligosaccharide for N-linked glycoproteins come from | Dolichol-P-P-oligosaccharide |
| when does Dolichol-P-P-oligosaccharide transfer on | co-translationally |
| Tunicamycin | inhibits an enzyme in the synthesis of dolichol-oligosaccharide donor |
| How is the oligosaccharide for N-linked glycoproteins changed | step-wise rxns |
| Where do changes to the oligosaccharide for N-linked glycoproteins occur | ER and Golgi |
| GPI anchor synthesis | assembled independently then transferred near the C-terminus of protein accompanied by C-terminus end cleavage |
| What determines blood type | carb structures on cell surface |
| Blood type O | nothing added to Gal |
| Blood type A | GalNAc added to Gal |
| Blood type B | Gal added to Gal |
| 3 types of coated vesicles | clathrin-coated, COPI-coated, and COPII-coated |
| major coat proteins | clathrin |
| what does clathrin do | provides physical budding force and vesicle formation |
| triskelion | clathrin 3 heavy chain and 3 light chain form a triskelion |
| adaptin | coat protein that’s a molecular link between clathrin and transmembrane receptors |
| what pinches off the clathrin coated bud using GTP | dynamin |
| COPI and COPII require | GTPase |
| Sar1-GDP | used in COPII; GDP-GTP to become active and lodges itself into the ER membrane |
| ARF-GDP | used in COPI; responsible for COPI and clathrin coat assembly at golgi membranes |
| COPI | golgi to ER |
| COPII | ER to Golgi |
| T-SNARE | target protein on membrane that v-snare finds |
| v-SNARE | on vesicle and finds t-snare |
| Rab protein | GTPase family protein that monitors SNARE fitting and hydrolyzes the GTP to lock the SNAREs together |
| Vesicular tubular cluster | the group of vesicles going from the ER to Golgi |
| How do vesicular tubular clusters move | along microtubules |
| ER retrieval signal | signal sequence that binds to COPI and are packaged for retrograde transport to the ER |
| KDEL | lys-asp-glu-leu; ER retrieval sequence; bind to KDEL receptors to be returned to ER |
| Where do regulated and constitutive secretory pathways diverge | TGN |
| What supplies the plasma membrane with proteins and lipids | constitutive secretory pathway |
| Regulated secretory pathway steps | selected proteins are sorted, packaged in clathrin coated vesicles at TGN, proteolytic cleavage occurs, triggered release in response to cell signal |
| Rab3 | a synaptic vesicle specific G-protein |
| What cells do phagocytosis | macrophages and neutrophils |
| Formyl-methionyl-peptides | macrophages recognize and phagocytize anything starting with this b/c prokaryotic proteins start with formyl-methionyl |
| Opsonozation | a bacterium must be opsonized (covered in IgG’s that are recognized by Fc receptor on macrophage or neutrophil) before it can be engulfed |
| Pinocytocis occurs in which cells | all |
| Nonselective pinocytosis | fluid-phase |
| Receptor-mediated pinocytosis | uptake of macromolecules; occurs in coated pits |
| 3 outcomes of receptor mediated endocytosis | recycles, degraded, transcytosis |
| 2 fxns of lysosomes | degradation of endocytic material and autophagy |
| residual body | lysosome when the enzymes are used up |
| with what are lysosomal enzymes tagged in the CGN | mannos-6-phosphate |
| M6P receptor proteins | transport lysosomal hydrolase from TGN to late endosome |
| I-cell disease | Inclusion cell disease;lack N-acetylglucosaminephosphotranspherase deficiency (lysosomal hydrolases get sent out of cell); lysosomes accumulate partly digested material (lots of inclusion bodies) |
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