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21 Cards in this Set
- Front
- Back
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Vesicular Traffic |
-mechanism by which cargo is transported within membrane-enclosed carriers called vesicles |
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What are the various sites between which vesicles carry cargo? |
-ER<--->Golgi -Golgi<--->Endosomal-Lysosomal Compartment -Golgi<--->Plasma Membrane/ Extracellular space -Endo/Lysosomal <---> Plasma Membr/ Extracell
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What are transport vesicles? |
-transport cargo, selective and directional -assembled within donor compartment |
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Clathrin |
--protein "coat" on the surface of a vesicle that directs it towards the endosomal/lysosomal compartment -can originate in the plasma membrane carrying plasma or extracellular cargo (endocytosis) -can originate in the golgi carrying newly synthesized lysosomal proteins |
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Coat Protein Complex I (COP1) |
-mediates retrograde transport -Golgi--> ER -within Golgi cisternae towards cis side |
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Coat Protein Complex II |
-mediates anterograde transport -ER--> Golgi -Golgi-->Plasma Membrane |
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SNAREs |
-interaction between vesicle SNARE (vSNARE) and target membrane SNARE (tSNARE) mediates vesicle fusion |
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How are proteins transported from the ER to the Golgi? |
-COPII- coated vesicles
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How are proteins transported within the Golgi apparatus? |
1. Vesicular Transport- Golgi cisternae each contain specific maturation enzymes -vesicles carrying cargo move sequentially from one cisternae to another and become progressively more modified -golgi cisternae are static, not dynamic 2. Cisternal Maturation Model- cisternae matures as it migrates through complex -specific enzymes move within COPI/ COPII vesicles -golgi is dynamix, not static |
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What are the functions of the Golgi Apparatus? |
1. Post-translational modifications 2. Assembly of protein complexes 3. Sorting proteins to final location (trans Golgi) -lysosomes, plasma membrane, secretory vesicles, back to ER 4. Membrane recycling |
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-Describe how post-translational modifications occur in the Golgi |
-O- and N-glycosylation: -O (for secreted proteins), N(for cell surface proteins) -all proteins that leave the ER have a high mannose oligosaccharaide code attached to them (due to modification in the ER) -In Golgi, mannose residues are removed by Golgi mannosidase I and II - N-acetylglucosamine transferase I: -adds NAcGIc groups to set up further and final modifications -initial oligosaccharaide core is the same (ER-modified) but final moiety varies from protein to protein (Golgi-modified) -Sulfation of proteins (tyr) and carbohydrates |
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Retrieval Signal |
-any sequence that triggers vesicular transport of a protein back to the ER -usually found in ER resident proteins |
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What is MEMBRANE RECYCLING? |
-internalization of membrane patches (endocytosis) are delivered to trans golgi -material from trans golgi is delivered to plasma membrane (exocytosis) |
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How are proteins transported from GOLGI to LYSOSOMES? |
-mediated by mannose-6-phosphate (M6P) and its receptor -in cis golgi, lysosomal enzymes becomes tagged with M6P due to phosphate addition by GlcNAc phosphotransferase -in trans golgi, M6P receptor recognizes these proteins, assembles lysosomal enzyme in a clathrin-coat that traffics to lysosome -once in lysosome, enzymes are unloaded and M6P receptor dissociates due to acidic pH -M6P receptor is recycled back to trans golgi
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Explain how ENDO H works |
-in golgi, mannose residues are gradually removed by golgi mannoisidase I and II -Endo H cleaves only high mannose residues -can be used to determine localization of the protein in the cell -proteins in the immature, high mannose form will be Endo H sensitive; found in ER and cis golgi -mature, modified proteins will be Endo H resistant; found in trans golgi or later in secretory pathway |
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What is EXOCYTOSIS? |
-release of cargo by fusion of the vesicles with the plasma membrane |
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How does EXOCYTOSIS occur? |
1. Constitutive pathway- carries cargo automatically from Golgi to plamsa membrane -continuous and not regulated 2. Regulated pathway- requires an extracellular signal for the delivery of the cargo -regulates the amount of receptors or channels in the plasma membrane (e.g. binding of insulin to receptor signals insertion of glucose channels in the plasma membrane, enhancing glucose uptake) -specialized cells, where secretion of chemicals only occurs after the appropriate signal |
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What is the function of LYSOSOMES? |
-intracelluar digestion -contain acid hydrolases able to digest a variety of substrates -lysosomal enzymes activated at low pH, which is established by a vacuolar H+-ATPase pump -lysosomes fuse with other vesicles, allowing lysosomal enzymes to come into contact with the cargo to be degraded |
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What is ENDOCYTOSIS? |
-cargo moves from cell surface into the inside of the cell. can occur by: 1. receptor-mediated-selective internalization due to binding of receptor on plasma membrane 2. phagocytosis- internalization of large particles within phagosomes -can be enhanced by presence of receptors 3. pinocytosis- nonspecific ingestion of fluid and small solutes |
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Describe how ENDOCYTOSIS works |
-after uptake, early endosome migrates towards cell interior, from which point cargo can: 1. continue to lysosomal degradation -early endosome-->multivesicular body--> endosome-->more acidic (H+- ATPase)--> fusion with lysosome 2. recycle back to plasma membrane 3. traffic to another region of the membrane |
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What is TRANSCYTOSIS? |
-transfer of cargo from one side of the membrane to another -does not result in lysosomal fusion, so no degradation -example) transfer of maternal antibodies from the luminal side (gut) to the apical side (blood) |
