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17 Cards in this Set
- Front
- Back
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What controls whether ribosomes are located on the ER or the cytosol? |
The protein sequence |
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What part of the protein sequence signals the ribosomes to move to the ER? |
A signal in the N terminus of the protein, usually first part transcribed |
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How does the protein end up inside the ER? |
The ribosome (or poly ribosome), mRNA and all translated proteins move to the ER when correct signal in protein occurs |
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How is the ER signal sequence recognized? (5 points) |
A Signal Recognition Particle (SRP) binds to series of hydrophobic amino acids on protein N terminus, and the ribosome which is attached Translation stops Complex binds to SRP receptor on outside of ER A translocation channel is 'recruited' by the SRP receptor. The ribosome binds to the channel and translates the protein through the channel |
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What happens to the signal N terminus on the protein once it has begun to be translocated through the ER channel? |
It is cleaved by signal peptidase |
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How many amino acids of alpha helix are required for a single transmembrane domain? |
20 |
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How is a transmsmbrane protein 'stuck into' the ER membrane? (3 points) |
The long sequence of hydrophobic amino acids also acts as a signal to stop the translocation The protein is released SIDEWAYS from the channel and into the membrane Rest of the protein is translated outside |
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How does the N terminus signal for translocation in a MULTIPASS protein act differently from one in a SINGLE pass protein? |
It is NOT a signal for peptidase, so not cleaved |
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How is a multi pass protein formed? (4 points) |
First N terminus sequence signals translocation by normal route BUT not a peptidase substrate so remains bound to the channel Transcription/translocation is paused at the NEXT long hydrophobic sequence Protein released out of channel, embedded in membrane, translation continues |
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Why can disulfide bonds NOT form in the cytosol? Why can they form in the ER? |
The cytosol is a reducing environment, the ER is an oxididative environment Disulfide bond is an oxidation reaction |
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What other modifications can occur to proteins in the ER? |
Formation of disulphide bridges and Glycosylation of proteins |
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Which protein keeps new proteins in the ER until correctly folded? What happens to incorrectly folded proteins? |
Charperones Incorrectly folded proteins are degraded |
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What occurs in the ER if there is an excess of misfolded proteins? |
Presence of more chaperones is triggered |
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How are more chaperones signaled for when unfolded proteins are present in the ER? (3 points) |
Unfolded protein inside ER binds to receptor
A transcription factor is activated and moves into the nucleus The factor activates transcription of chaperones |
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How are chaperones and similar proteins returned to the ER if secreted with proteins? |
The carry a C terminal ER retention signal (Usually KDEL) KDEL bind golgi receptors which re secrete it back to the ER |
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Where does Lipid Synthesis occur? |
The cytosolic layer of the smooth ER |
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What does the filppase enzyme do? |
Allows the bottom leaflet of the bilayer to grow by relocating synthesized lipids. (down the conc gradient) |
