Term
| How are proteins brought into the ER? |
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Definition
| co-translationally. Signal secquence is recognized by SRP. SRP receptor, on ER, recognizes SRP. The SRP is displaced as the protein is brought through the translocon. Then the signal sequence is cleaved. |
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Term
| What is special about the signal sequence for proteins destined to the ER? |
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Definition
| it is hydrophobic, about 8AAs, at the N terminus. It is cleaved by signal peptidase in the ER. |
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Term
| How do proteins that need to be transmembrane spanning get into the ER membrane? |
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Definition
| The same process, except there is a stop-transfer-sequence. |
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Term
| What is special about stop-transfer-sequences? |
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Definition
| They are hydrophobic AAs. When it is recognized by the translocon, it gets released from the channel and is dragged into the plane of the membrane. |
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Term
| Are there ways to get a protein into the ER besides the N-terminal start-transfer sequence? |
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Definition
| yes, there can be internal sequences also recognized by the SRP. |
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Term
| How would you get multiple-pass membrane spanning proteins into the ER membrane? |
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Definition
| Have an internal start-transfer sequence, so that a loop sorta goes down into the translocon. Then have a stop transfer (hydrophobic) sequence on both sides of the loop so that the appropriate areas stay in the membrane. |
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Term
| What does protein disulphide isomerase do? |
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Definition
| It is an enzyme that catalyzes protei folding by facilitating di-sulfide bond formation. it breaks unwanted disulfide bonds and rejoins wanted bonds. it does this by making a disulfide bond and exchanging it to the right spot. |
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Term
| What is one way proteins in the ER are tagged as being improperly folded? |
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Definition
| Many proteins are gylcosylated with a oligosaccharide tag (N-linked) which somehow shows whether things are folded properly and stuff. If the oligosaccharide is detected as in the wrong conformation, the protein will get kicked out of the ER. |
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Term
| What happens to improperly folded proteins in the ER? |
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Definition
| They get sent into the cytoplasm, are deglycosylated, get ubiquitinated, sent to the proteasome, and degraded. |
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Term
| What happens in the ER when it gets stressed about fucking up its job and having too many unfolded proteins? |
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Definition
| The Unfolded Protein Response (UPR) is kicked into action. With overwhelming beauty and strength, the Unfolded Protein Response uses its superhero powers to make things all good again, bitch. Basically, there aren't enough chaperones around--thats why the proteins are misfolding. SO, the UPR activates a signal transduction cascade to stimulate transcription of a regulator that translocates to the nucleus where it induces the transcription of chaperones. Extreme response leads to apoptosis. |
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Term
| Why would a protein chaperone for the ER not just be translated in the nucleus and all that? |
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Definition
| Well, idiot. basically translation happens on ribosomes in the cytoplasm or attached to the ER. SO, you get a transcription factor which goes to the nucleus, get an mRNA transcript which goes to a ribosome, and then you get a protein translocated co-translationally to the ER (think SRP). greatttt. |
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Term
| Why is this stuff all really important? |
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Definition
| It isn't really, so get over it. |
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Term
| Whats the point of vesicles? |
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Definition
| They bring soluble proteins between compartments. They also bring membranes between compartments (and thus transmembrane proteins). |
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Term
| How does transport between the ER and Golgi occur? |
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Definition
| budding and fusion of vesicles |
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Term
| What are two important goals of vesicle formation? |
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Definition
| Bring only the protein you want to transport, and bring it only to the place it is supposed to go. |
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Term
| What's the role of vesicles in ejaculation of semen? |
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Definition
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Term
| What kind of proteins do lysosomes degrade? |
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Definition
| They help with turnover of old-proteins in the cell that need to be replaced. |
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Term
| Vesicles going from ER to Golgi have what kind of protein coat? |
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Definition
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Term
| Vesicles going from golgi to ER have what type of protein coat? Why would proteins go from Golgi to ER? |
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Definition
| They have COPI, this is important because proteins sometimes mistakenly get taken to the Golgi from the ER in COPII vesicles. |
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Term
| How do vesicles travel from the ER to the Golgi? |
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Definition
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Term
| In which direction are proteins sorted in the golgi? |
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Definition
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Term
| What are the three functional compartments of golgi apparatus cisternae? |
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Definition
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Term
| Which direction is the cis golgi oriented? the trans golgi? |
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Definition
| The cis Golgi faces the ER. Trans face secretory vesicles or lysosomes. |
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Term
| What type of protein coat do vesicles headed for the lysosome from the trans Golgi have? |
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Definition
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Term
| What type of protein coat do vesicles headed from the plasma membrane to endosomes have? |
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Definition
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Term
| What happens after a clathrin-coated vesicle buds? |
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Definition
| The clathrin dissociates so that it can be recycled. |
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Term
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Definition
| They help to recruit clathrin to newly budding vesicles, and they help to make the vesicles have the proper structure for budding. |
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Term
| How are molecules for transport captured by vesicles? |
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Definition
| There are transmembrane receptors for these molecules. These are called cargo receptors. When they are captured, a vesicle will bud because of a conformational change in the cargo receptor when protein is captured. Adaptin will be recruited and also clathrin,for example. |
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Term
| What is a place in the body where vesicles travel from cell to cell? |
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Definition
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Term
| Can unfolded proteins get into vesicles? |
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Definition
| Usually not. They are usually bound to chaperones, so can't bind cargo receptors. |
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Term
| What causes vesicles to fuse together? |
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Definition
| a tethering protein on the target binds to the Rab protein on the surface of the incoming vesicle. Then, V-SNARE on the vesicle binds T-SNARE on the target. The SNARE proteins function as lock and key, causing vesicle fusion. |
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Term
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Definition
| They bind GTP and ensure specificity of binding between vesicles. Vesicle binding is important, because vesicles sometimes bind to share travel on a microtubule. Vesicles also use Rab and snare to bind membranes of organelles etc. Each type of vesicle has a specific Rab on it that functions as a marker. |
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Term
| How do botulinum toxin and tetanus toxin work? |
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Definition
| They cleave snares so that vesicles can't deliver their payloads in synapses. |
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Term
| How do proteins destined for the ER stay there? |
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Definition
| They have a special c-terminal ER retention signal (KDEL) which is recognized by ER and Golgi membrane proteins. |
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Term
| What happens if a protein from the ER gets into the Golgi that has the KDEL accidently? Also tell us the coats that would be involved on any vesicle transport. |
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Definition
| Well, the Golgi would recognize the KDEL receptors and transport the proteins back to the ER in COPI coated vesicles. They came over in COPII. |
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Term
| How do SNARES facilitate vesicle fusion? |
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Definition
| They bring the vesicles into very close contact with another (or the vesicle in close contact with the plasma membrane). |
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