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Why does SRP arrest translation after it binds to the signal sequence

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Question 1 of 5;Why does SRP arrest translation after it binds to the signal sequence and only the first 70 amino acids of the protein have been synthesized?;A. Most secretory proteins are only 70 amino acids long (7 kDa) so translation is completed by the time SRP binds.;B. SRP arrests translation to allow the exposed signal sequence to be cleaved from the protein before it enters the translocon.;C. SRP arrests translation so the signal sequence is not misfolded within the interior of the protein.;D. SRP does not arrest translation. The SRP receptor arrests translation after SRP docks the ribosome and newly synthesized protein on the ER.;Question 2 of 5;What is the purpose of GTP hydrolysis when SRP binds to the SRP receptor?;A. It's a source of energy to allow protein synthesis to resume.;B. It causes SRP to dissociate from the signal sequence, ribosome and SRP receptor.;C. It "hands off" the ribosome to the translocon;D. (a) & (b);E. (b) & (c);Question 3 of 5;How does a single P54SRP bind to diverse ER signal sequences that do not have identical amino acid sequences?;A. Multiple D & E on P54SRP form electrostatic bonds with ?core? K & R present on all signal sequences.;B. Multiple K & R on P54SRP form electrostatic bonds with ?core? D & E present on all signal sequences.;C. Multiple polar amino acids on P54SRP form hydrogen bonds with ?core? polar amino acids present on all signal sequences.;D. Cells have multiple isoforms of P54SRP that interact specifically with distinct ER signal sequences.;E. Multiple hydrophobic amino acids on P54SRP form van der Waals interactions with ?core? hydrophobic amino acids present on all signal sequences.;Question 4 of 5;The membrane spanning?-helix of a type I integral membrane protein such as the LDL receptor or Glycophorin A;A. Is referred to as an "internal signal anchor" and ensures that the N-terminal portion of the protein that precedes it will be inserted into the ER lumen and the C-terminal portion of the protein that follows it will remain in the cytosol.;B. Is referred to as an "internal signal anchor" and ensures that the N-terminal portion of the protein that precedes it will remain in the cytosol and the C-terminal portion of the protein that follows it will be inserted into the ER lumen.;C. Is referred to as an "stop-transfer anchor" and ensures that the N-terminal portion of the protein that precedes it will be inserted into the ER lumen and the C-terminal portion of the protein that follows it will remain in the cytosol.;D. Is referred to as an "stop-transfer anchor" and ensures that the N-terminal portion of the protein that precedes it will remain in the cytosol and the C-terminal portion of the protein that follows it will be inserted into the ER lumen.;Question 5 of 5;You're studying the Na+/K+ ATPase in a certain cell line. (Remember, it's present in virtually all cells so the particular cell type doesn't matter here). You have 4 samples of these cells that have identical #s of Na+/K+ ATPases.;Sample 1 are the control cells that are not treated with anything. They retain 100% Na+/K+ ATPase activity throughout the experiment.;Sample 2 is treated continuously with a sufficiently high dose of the cardiac glycoside oubain that you see 100% inhibition of Na+/K+ ATPase activity 6 hours later in the oubain treated cells. 100% Na+/K+ ATPase activity is still inhibited 12 hours later.;Sample 3 is treated continuously with a sufficiently high dose of an siRNA that completely degrades the mRNA encoding the? subunit of the Na+/K+ ATPase in less than 30 minutes. However, you observe that only 50% of Na+/K+ ATPase activity is inhibited 6 hours later in the siRNA-treated cells even though all the? subunit mRNA has been degraded. Only 25% of Na+/K+ ATPase activity remains 12 hrs after siRNA treatment.;Sample 4 is treated continuously with a sufficiently high dose of the general protein synthesis inhibitor, cycloheximide. However, you observe that only 50% of Na+/K+ ATPase activity is inhibited 6 hours later in the cycloheximide-treated cells even though all protein synthesis has been inhibited. Only 25% of Na+/K+ ATPase activity remains 12 hrs after cycloheximide treatment.;What can you conclude from this experiment?;A. siRNA and cycloheximide only partially inhibit Na+/K+ ATPase activity.;B. oubain completely inhibits both Na+/K+ ATPase activity and its synthesis.;C. Oubain completely inhibits Na+/K+ ATPase synthesis but not its activity.;D. The half-life of the? subunit protein is 6 hrs.;E. You cannot conclude anything from this experiment.

 

Paper#15248 | Written in 18-Jul-2015

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