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21 Cards in this Set
- Front
- Back
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The following categories of proteins have been synthesized and incorporated into the the rough ER by co-translational import
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Proteins secreted from cells
Most integral membrane proteins Soluble proteins that will reside within compartments of the endomembrane system (ER, Golgi complex, lysosomes, endosomes, vesicles, plant vacuoles) |
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1)If the protein is to be a glycoprotein_________
2) 3 theories of movement of materials? |
carbohydrates are added to the protein by enzymes in the RER lumen
2)cisternal maturation model vesicular transport model combined |
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If the protein is to be a glycoprotein_________
The ER lumen also contains the enzyme __________ that___________ The proteins are then _______ on a ________ |
carbohydrates are added to the protein by enzymes in the RER lumen
PDI that catalyzes formation of disulfide bridges transferred on a vesicle to the ER-Golgi Intermediate Compartment (ERGIC) and thence to the Golgi complex |
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describe the golgi complex and how it was discovered
2) the cis/trans nature of golgi causes it to be what? |
discovery....
Discovered by Camillo Golgi (1898) Stained cell sections with a solution of silver nitrate applied to tissue that had been soaked in osmium & bichromate Saw darkly staining reticular network near nucleus; he got the Nobel Prize in 1906 structure... Flattened, disk-like membrane cisternae with dilated rims, from which vesicles bud off. Golgi cisternae polarized cis face (closest to ER); trans face (other end; closer to plasma membrane); polarization reflects role as processing plant – material inside the cisternae flows from cis to trans. 2)polarized |
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functions of golgi complex
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Newly synthesized membrane, secretory & lysosomal proteins leave ER & enter at cis face of Golgi
Proteins pass across the Golgi stack to the trans face; during transit, proteins are sequentially modified in specific ways: 1)Part of the protein's length may be trimmed by proteolytic enzymes 2)Amino acids may be modified (hydroxylation of lysine & proline residues of collagen) 3)Carbohydrate content of glycoproteins can be modified by series of stepwise enzymatic reactions At the trans face of the Golgi system, the proteins are sorted & targeted for delivery by vesicles to their ultimate location (e.g. plasma membrane, lysosome etc.) |
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Cisternal maturation model
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Cisternae form at the cis face by ER/ERGIC vesicle fusion, travel to trans face & are altered along the way
Cisternae mature & change in composition as they move through Golgi; each cisterna matures into next cisterna along stack |
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Vesicular Transport Model (mid-1980s until late-1990s)
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Cisternae remain in place as stable compartments held together by protein scaffold. Cargo is shuttled through the Golgi stack from by vesicles budding from one cisterna & fusing vesicles to next one
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cis cisternae can mature into what?
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trans cisternae
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are the two models of how golgi system works exclusive?
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no....many people believe in a combined model as well
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how is cargo transported...simple answer
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Cargo is transported by vesicles both an anterograde (cis trans) and a retrograde direction (transcis and thence to ER).
mn:ant and cat |
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anterograde
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anterograde (cis to trans)
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retrograde direction
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retrograde direction (transto cis and thence to ER).
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Vesicles may be used for rapid transport of cargo to ________ , while cisternal maturation is moving other materials _______
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trans face
at a more leisurely pace |
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Why are vesicles moving in BOTH directions through the Golgi complex (cis to trans AND trans to cis)?
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The cis to trans movement predominates, carrying cargo (membrane and soluble proteins) for export. These cargo’s are eventually recognized by binding proteins at the trans face and filtered into secretory vesicles etc.
The trans to cis movement returns enzymes that belong to the Golgi complex but that were swept up in the flow of vesicles containing cargo This recycling means that targeting of proteins to vesicles emerging from each stack does not have to be 100% accurate. |
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So how are vesicles moving from one stack to another in the cistrans (anterograde direction) distinguished from those traveling in the transcis (retrograde) direction?
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The two types of vesicles have different protein coats surrounding their bilayer.
mn:picture 2 cops as ants in a car Anterograde vesicles – COPII coats Retrograde vesicles COPI coats |
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describe why COPII coated vesicles would be important
what protein can regulate the cop11 complex and what will it do? |
E.g. Budding of of COPII coated vesicles from the ER and cis Golgi stacks– intended to carry newly synthesized proteins towards trans Golgi stacks.
Transmembrane proteins in the COPII coat of the budding vesicles act as receptors for newly synthesized secretory proteins (cargo), concentrating them in the lumen of the budding new vesicle. A GTP-binding protein, Sars-GTP is also recruited to the coat of the budding vesicle. This protein acts as a “self-destruct timer”. If the GTP on Sars is hydrolysed before the vesicle fuses with the cis-Golgi stack, the COPII coat will fall apart and the vesicle will be destroyed. Ensures that vesicles that do not find their correct target are destroyed before fusing with something inappropriate |
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What can a COP1 vesicle be used to retrieve?
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Use of COPI coated vesicles to retrieve ER and cis Golgi proteins accidently swept into trans Golgi along with cargo
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describe how COP1 coated vesicle retrieves stuff
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Proteins that normally reside in ER (in lumen & membrane) have short amino acid sequences at C-terminus that serve as retrieval sequence – e.g KDEL
Retrieval of escaped ER proteins is accomplished by specific receptor proteins in the trans Golgi stacks that capture the molecules & return them to the cis stacks and ER in COPI-coated vesicles Each biosynthetic pathway compartment may have its own unique retrieval signal; explains maintenance of unique protein complements in each one despite constant flow of vesicle movement. Mn: Kara dell was bobby dell's mom who was the only women cop |
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Sorting proteins emerging from the trans Golgi stacks:
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One function of the trans Golgi stacks is to sort proteins into vesicles bound for target organelles.
This sorting process has several similarities to those we have seen so far: Formation of vesicles with a specific protein coat Recognition signals on cargo proteins (short peptide sequences or special sugar sequences for some glycoproteins) membrane receptors in budding vesicles that bind to cargo proteins |
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An example of protein sorting at the trans-Golgi
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targeting Clathrin coated vesicles to lysosomes
Soluble enzymes bound for lysosomes are a class of glycoproteins that are recognized by the receptor proteins attached to the clathrin coat These glycoproteins are first “tagged” by enzymes in the Golgi Phosphate groups are attached to mannose sugar residues in their carbohydrate chains The phosphate groups are recognized by a mannose-6-phosphate receptor protein associated with the clathrin coat, creating coated vesicles that are targeted to fuse with lysosomes and replenish enzymes there. Proteins bound for inclusion in lysosomes are packaged into clathrin coated vesicles The clathrin coat has three main components Adaptor proteins that link clathrin to integral membrane receptor proteins for cargo proteins Receptor proteins that bind appropriate cargo proteins picture in lecture notes |
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Clathrin
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a protein that forms an outer scaffold around the budding vesicle.
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