1. Which cytosolic factor is most likely to associate with the signal sequence of a protein that is targeted co-translationally to the ER?
A chaperone of the Hsp70 family
The translocation channel
The ribosome
Signal recognition particle (SRP)
Signal peptidase
2. What is the most likely fate of a protein with an N-terminal hydrophobic sorting signal and an additional internal hydrophobic domain of 22 amino acids?
The protein stays in the cytosol
The protein is transported to mitochondria
Because the protein has an N-terminal sorting signal, the protein is translocated all the way into the ER lumen
The hydrophobic domain is recognized as a transmembrane domain once it is in the translocation channel and released sideways into the membrane
The hydrophobic domain is cleaved off by signal peptidase
3. Which of the following statements best describes N-glycosylation? N-glycosylation refers to........
the addition of a pre-formed sugar tree to a serine or threonine present in the cytosolic domain of a protein
the addition of a pre-formed sugar tree to a phospholipid to make a glycolipid
the addition of individual sugars to selected amino acids on a protein
the addition of a pre-formed sugar tree to an asparagine residue found within the consensus sequence Asn-X-Ser/Thr in an ER lumenal domain of a protein
the addition of a pre-formed sugar tree to an asparagine residue found within the consensus sequence Asn-X-Ser/Thr in a cytosolic domain of a protein
4. What is the most likely fate of a protein in which a mutation has led to misfolding in the ER?
It is sequestered by the proteasome in the cytosol
It is first tagged with ubiquitin in the ER and then degraded by the proteasome in the cytosol
It is first moved out of the ER, tagged with ubiquitin in the cytosol and then degraded by the proteasome in the cytosol
It associates with many chaperones in the ER, which guarantee its correct folding
Its misfolded state is recognized by chaperones in the ER, which will induce the protein's degradation by the proteasome in the ER.
