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29 Cards in this Set
- Front
- Back
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Why are cells compartmentalized?
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Things like proteases and TCA cycle enzymes would break down everything
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In what direction are mRNA translated?
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5' to 3' or N terminus to C terminus
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What is the default destination of a newly made protein?
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cytoplasm
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What type of cells secrete tons of proteins?
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pancreas cells
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What organelles (in order) are involved in the secretory pathway?
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endoplasmic reticulum, golgi apparatus, secretory vesicles, outside cell
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A protein that will be secreted from the cell is bigger, smaller, or same size in vitro?
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bigger
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A protein that would not be secreted from the cell will be bigger, smaller, or same size in vitro?
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same size!
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What is the signal hypothesis?
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Information in a protein controls secretion. This info is cleaved off during the process of secretion
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What is the signal hypothesis?
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Information in a protein controls secretion. This info is cleaved off during the process of secretion
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What is the hard way to traffick proteins called? What are the two main types?
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Post translational import: 1. Make protein, unfold it, insert it. 2. Make protein, prevent it from folding, insert
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What is the easy way to traffick proteins called?
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Co translational import: begin translating protein, SRP recognizes signal sequence, stops translating. Everything to endoplasmic reticulum.
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For a secreted protein, where and what is the signal sequence?
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two positively charged amino acids followed by 20 hydrophobic amino acids (start signal sequence), followed by a couple polar amino acids (++[20 hydrophobic]pos------)
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What does the signal recognition particle (SRP) do?
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stops translation, takes mRNA, ribosome and little protein bit to the rough endoplasmic reticulum
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What happens when SRP and co. dock at the ER?
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SRP, SRP receptor and GTP all bind. Pore (translocon) opens and polypeptide (start of protein) is inserted. GTP is hydrolyzed and SRP is released.
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What are the parts of a translocon? How is it shaped?
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Outside ER: two negatively charged AAs. Inside translocon: hydrophobic patch on one side, hydrophilic patch on other
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What does signal peptidase do?
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Reacts to polar AAs after the start signal sequence and cleaves, allowing threaded protein into ER.
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If a protein (or part of protein) is inside a vesicle (or inside the ER), will it end up inside or outside of the cell?
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Inside the vesicle, means outside the cell.
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How was cotranslational import proved necessary for secretion?
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1. Removed signal sequence from lysozyme (usually secreted). 2. Lysozyme ended up in cytoplasm
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How was cotranslational import proved sufficient for secretion?
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1. Added signal sequence of lysozyme to a cytoplasmic protein (they used green flourescent protein). 2. It all ended up outside the cell (glowing green)
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Type I Transmembrane Protein: How does it work?
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1. Has an N terminus signal sequence (just like secreted proteins). 2. Also has a stop transfer sequence (just a stretch of 20 hydrophobic AAs.) 3. Moves out through opening in translocon into ER membrane
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Type I Transmembrane Protein: Which side inside cell, which outside?
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N terminus inside ER and outside cell. C terminus in cytoplasm, stays in cytoplasm
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Type II Transmembrane Protein: How does it work?
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1. N termninus does not have a signal sequence. 2. Start transfer sequence later on. Just like stop transfer sequence except it lacks the polar AAs at the end (so it doesn't get cleaved)
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Type II Transmembrane Protein: Which side inside cell, which outside?
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C terminus inside ER and outside cell. N terminus in cytoplasm, stays in cytoplasm
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Multi Spanning Protein: How does it work?
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Many start/stop transfer sequences
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Multi Spanning Protein: How to tell what's inside or outside cell?
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1. If first start transfer sequence is AT N terminus (like type I), then next stretch of AAs will be inside ER/ outside cell, then switching after each. 2. If first start transfer sequence is in a little from N terminus (like type II), part before it will be in cytoplasm, and part after it will be in the ER/outside the cell.
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How do mitochondria and chloroplasts get their proteins?
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Post translational import, specifically by preventing protein from folding while it's being transcribed
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Post Translational Import: What is the N terminus information?
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An amphipathic alpha helix (one side hydrophobic, one side positively charged)
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Post Translational Import: How does it work?
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The amphipathic helix recruites chaperones (HSP70)
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Post Translational Import: What does HSP70 do?
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A chaperone, it wraps the protein around itself (like the seams of a baseball), to prevent it from folding
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