Term
| what do cells depend on to ensure they arrive at their subcellular destinations/or are secreter? |
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Definition
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Term
| what happens to proteins with NO targeting signals? |
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Definition
| they are translated entirely on free ribosomes and remain in the cytoplasm. |
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Term
| what 4 things recieve proteins from the cytosol? |
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Definition
| mito, chloro, nucleas, and peroxisomes |
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Term
| mito, chloro, nucleas, and peroxisomes receive proteins from where? |
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Definition
|
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Term
| when do mito, chloro, nucleas, and peroxisomes receive proteins from the cytosol? |
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Definition
| after their translation (on free ribosomes) is complete |
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Term
| what are ER, golgi, lysosomes, plasma membrane and secreted proteins translated by? |
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Definition
| RER ribosomes. and they are TRANSLOCATED at the same times. |
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Term
| how do ER, golgi, lysosomes, plasma membrane and secreted proteins arrive at their destinations? |
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Definition
| they arrive at other locations via vesicles budding and fusing |
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Term
| the ______ of organelles of the secretory pathway are ____________ equivilent to each other and to the _________ of the cell |
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Definition
lumen
topologically
exterior |
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Term
| what does protein targeting selectively recognize? and how do they recognize them? |
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Definition
| recognize nacent proteins with signal sequences. |
|
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Term
| what does the signal sequence bind to? and what does this cause? |
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Definition
| the signal sequence bings to a signal recognition particle (SRP) which causes tsl to temporarily stop |
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Term
| what 3 things arrive at the ER inact with a ribo receptor? and what happens? |
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Definition
1. ribosome
2. nascent polypeptide
3. SRP
a channel, part of the translocon, opens, the nascent proteins begin to be COTRASLATIONALLY TRANSLOCATED |
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Term
| how to proteins enter the secretory pathway? |
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Definition
| by translocation across the ER membrane |
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Term
| what do proteins use signal sequences for? |
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Definition
| to targe the ER for transLOCATION |
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Term
| when was the signal hypothesis proposed? and what does it explain? |
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Definition
| proposed in the 1970's. it explains how proteins got targeted to the RER. |
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Term
| when is the ER-targeting signal sequence normally cut off? |
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Definition
| in the lumen of the RER. after the protein begins its transLOCATION |
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Term
| when is a nascent proteins termed? and prior to what is it termed this? |
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Definition
| it is termed a preprotein b/c it still has a signal. it is termed this prior to its signal sequence removal. |
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Term
| what happens to a normally bound ER protein? |
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Definition
| it is synthesized in an in vitro cell-free system, it is LARGER, and migrates more SLOWLY. |
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Term
| when translated in vitro in the presence of purified ER micosomes, what happened to the protein? |
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Definition
| it was smaller (migrated faster) and was located in the ER lumen (microsome lumen) |
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Term
| what are signal sequences recognized by? |
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Definition
| they are recognized by the signal recognition particle (SRP) |
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Term
|
Definition
| it is a ribonucleoprotein particle |
|
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Term
|
Definition
| it is made of 6 polypeptides and a small (7s) RNA molecule |
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Term
|
Definition
| part of a SRP (its a G-protein) |
|
|
Term
| what does the part of a SRP that binds to the nascent polypeptides signal sequence have? |
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Definition
| it has a large number of MET residues (hydorPHOBIC) |
|
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Term
| what does part of SRP bind to? and what effect does this have on its translation? |
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Definition
| ribosomes, and this slows translation until docking at the ribosome. |
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Term
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Definition
| a SRP receptor. it is a dimer of two subunits. SRo< (on c-face, interacts with SRP) and SR Beta (transmembrane and part of non-c face) |
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Term
| SRo< and SR beta are what? |
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Definition
| GTP-binding proteins (G-proteins, GTPases) |
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|
Term
| what is required by SRP and SR? |
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Definition
| coordinated GTP-binding and hydrolysis are reqiured by them |
|
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Term
| why is GTP-binding and hydrolysis required by SRP and SR? |
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Definition
| they are required for proper targeting of nascent chains to the ER, and for their transfer to the transLOCATION channel and the recycling of SRP to the cytosol. |
|
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Term
| what happens when SRP releases the ribosome? |
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Definition
| the ribosome engages the translocon, and the nascent polypeptide begins the translocation |
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|
Term
| what begins translocation? |
|
Definition
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