Term
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Definition
| groups of ribosomes in a short spiral array that are attached to a thread of mRNA and to the membrane of the rER |
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Term
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Definition
| The signal sequence is a set of neutral amino acids found on the amino-terminus of a newly synthesized protein that signal that the protein needs to be translated into the rER. |
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Term
| How proteins reach and enter RER |
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Definition
| The signal sequence interacts with a signal-recognition particle (SRP), which arrests further growth of the polypeptide chain. The SRP-polyribosome complex is the relocated to the rER membrane. SRP binds to a docking protein on the cytoplasmic surface of the ER, which aligns the ribosome with the translocator, which is an integral protein of the rER. This binding to the translocator cuases dissocation of the SRP-dockingprotein complex, allowing the ribosome ot resume protein synthesis. The translocator then inserts the polypeptide chain into its aqueous pore, allowing the new protein to enter the lumen of the rER |
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Term
| Possible destinations of proteins localized to RER |
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Definition
| Proteins are normally delivered to the Golgi apparatus within minutes. Proteins in the rER can also be exported back to the cytoplasm if they are not modified correctly. A few proteins rER membrane proteins will just stay in the rER instead of being exported to the Golgi |
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Term
| What happens to proteins without signal sequence |
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Definition
| are translated and remain in the cytoplasm. |
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Term
| post-translational modifications that take place in the RER |
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Definition
| protein modification includes core glycosylation, disulfide bond and internal hydrogen bond formation, folding of the newly synthesized protein with the help of molecular chaperones, and partial subunit assembly. |
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Term
| α1-antitrypsin deficiency |
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Definition
| Α1-antitrypsin (A1AT) deficiency is when a single aa substitution prevents the rER from exporting A1AT to the Golgi. This leads to decreases in A1AT activity in the blood and lungs and deposition of defective A1AT within the rER of liver cells. |
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Term
| fate of misfolded proteins |
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Definition
| eventually degraded by proteasomes after being tagged for destruction with ubiquitin |
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Term
| location, structure and function of proteasome |
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Definition
| Proteasomes are large cytoplasmic or nuclear ATP-dependent protein complexes. Each proteasome has a hollow cylinder that contains a 20S core particle (CP) that facilitates the protease activity and a 19S regulatory particle (RP) at the end of each CP (2 total) that regulates entry into the destruction chamber |
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Term
| role and fate of ubiquitin in proteasomes |
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Definition
| Misfolded proteins are repeatedly tagged with ubuquitin by three ubiquitin ligages called ubiquitin-activating enzymes E1, E2 and E3. The tagged protein is then degraded by the 26S proteasome complex. After degradation, the free ubiquitin molecules are released by de-ubiquitinating enzymes (DUB) and are recycled |
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Term
| pathological conditions of malfunction of proteasomes |
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Definition
| Loss of proteasome function due to mutations in the system of ubiquitin-activating enzymes leads to a decrease in protein degradation and their subsequent accumulation in the cell cytoplasm. Pathological conditions can also occur due to accelerated degradation of proteins due to overexpression of proteins involved in this system. |
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Term
| what organelle receives proteins from RER? |
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Definition
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Term
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Definition
| Anterograde transport is movement from the rER to the cis-Golgi face and utilizes vesicles coated in COP-II |
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Term
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Definition
| Retrograde transport is movement from the cis-Golgi face back to the rER and utilizes COP-I |
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Term
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Definition
| sER is involved in detoxification and conjugation of noxious substances. It is also involved in lipid and steroid metabolism, glycogen metabolism, and membrane formation and recycling. |
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Term
| cis, medial and trans faces of Golgi. Flow of proteins in Golgi in processing |
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Definition
| The cis face is the forming face and is located closest to the rER. The trans face is the maturing face and is located farther away from the rER. The medial Golgi lies in between the cis and trans faces. |
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Term
| what types of cells have abundant Golgi |
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Definition
| secretory cells, such as plasma cells, osteoblasts, and cells of the epididymis |
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Term
| major functions of Golgi in protein processing |
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Definition
| glycoproteins and glycolipids have their oligosaccharides trimmed and translocated. Glycosylation of proteins and lipids occurs. M-6-P is added to proteins destined to travel to late endosomes and lysosomes. Glycoproteins are phosphorylated and sulfated. Some proteins are also proteolytically cleaved |
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