Intracellular compartments and protein targeting
If a protein has a __________, it is likely unfolded when it reaches its target membrane:
a. Ran binding domain
b. Nuclear localization sequence
c. Peroxisome targeting sequence
d. Presequence
Presequence
Which inner membrane components are involved in the import of mitochondrial targeted proteins?
a. TIM 23 Complex
b. TOM Complex
c. OXA Complex
d. a and b
e. a and c
A and C
Which of the following is true regarding N glycosylation?
a. It is PTM that occurs in all proteins imported into the ER
b. Three terminal sugars are used to monitor protein folding
c. Glucosidases remove glucose from N-glycosylation
d. All of the above
All of the above
Arf GTPases associated with clathrin coated vesicles do not need a GAP in order to efficiently hydrolyze GTP
T/F
false
Clathrin coats contain an ArfGAP, which stimulates Arf GTP hydrolysis and inactivation
If a cell has a non-functional dynamin protein, which of the following events would NOT take place:
a. ER to Golgi transport
b. Golgi to ER transport
c. Golgi to Endosome transport
d. Glycolysation defect
Golgi to Endosome transport
Which ER translocation channel is involved in co-translational protein import.
a. Sec 61 complex
b. Sec 62/63
c. SRP-SR
d. All of the above
Sec 61 complex
Mitochondrial presequences are usually ___ amino acids in length and have an alpha-helix that is ___
18-36, amphiphilic
You found that the same protein purified from a diseased cell type (right lane; Protein B) runs differently on a gel compared to the protein purified from a normal cell (left lane; Protein A). Upon investigation you found that the Protein B is of the same length as Protein A but has a single point mutation at an Asn residue. Which one of the following can be possible explanation:
Protein B failed to undergo N-glycosylation at ER
You found a lot of clathrin coated vesicles accumulating in the cytoplasm. Which of the following may not be a possible explanation for your observation:
a. Loss of function mutation in an Arf GEF
b. Loss of function mutation in a Rab GTP
c. Mutation of a t-SNARE protein
d. Both a and c
e. All of the above
Loss of function mutation in an Arf GEF
You see a lot of protein build-up in the lysosome as lysosomal proteases are no longer functional. Upon investigation you notice that the H+ pump on the lysosomal membrane has a loss of function mutation. Which of the following statements might explain your observation:
a. Lysosomal protease uses H+ pump as a co-enzyme
b. Lysosomal protease has high affinity for proteins destined for degrardation
c. Lysosomal protease cannot function in a basic environment
d. Lysosomal protease can no longer to bind to H+ pump
Lysosomal protease cannot function in a basic environment
You have discovered a new soluble protein, ELAD, and hypothesize this protein is targeted for the ER. You decide to generate a green fluorescent fusion protein to monitor its movement through the cell. Where should you attach the fluorescent tag to test your hypothesis?
Internally or C terminus. If you place the tag at the N terminus, it will mask the signal sequence and the protein will not reach the ER.
A protein encoded by a nuclear gene has two N-terminal mitochondrial targeting sequences that are ultimately removed from the protein. In which mitochondrial compartment will this protein reside? Explain
The first signal sequence will bring the protein through both outer and inner membranes to the lumen. The second signal sequence will bring the protein back through the inner membrane into the intermembrane space
You are working with a cell line. You saw a buildup of ER originated unfolded protein in the cytosol and for some reason they are not being degraded by proteasome machinery? Upon investigation you found all these unfolded cytosolic proteins are glycosylated. Which protein do you think is mutated and why?
N-glycanase. After unfolded proteins are translocated into the cytosol, N-linked glycosylation has to be removed for proteasome degradation.
Which of the following determines the specificity of clathrin coated vesicle trafficking:
a. Adaptor proteins
b. Clathrin heavy chain proteins
c. Sec23/24 complex proteins
d. Membrane topology
e. All of the above
Adaptor proteins
Pinocytosis occurs in what structure?
a. Outer membrane of ER
b. Inner leaflet of Mitochondria
c. Cellular membrane
d. Nuclear membrane
Cellular membrane
A soluble protein is normally targeted to the ER. You fused GFP (green fluorescent protein) to the C terminus. Now the protein is being secreted extracellularly. Why did this protein change location and what sequence may you have masked?
By fusing GFP to the C terminus, you masked the KDEL sequence which localizes the soluble protein in the ER lumen. So now the protein will be secreted instead.
****Daily Double****
For the following questions, answer type I, type II, type III, or soluble protein, or any combination of the four.
Contains charged residues flanking their signal sequence
Involves processing by a signal peptidase
Has their N terminus in the cytosol
Has their N terminus in the ER lumen
Contains an N terminal signal sequence
a. Type II and Type III
b. Type I and soluble
c. Type II
d. Type I, Type III, and soluble
d. all of them
Due to cellular stress, the ER is unable to fold proteins properly. What are the consequences of this?
Misfolded protein will accumulate in the ER, triggering unfolded protein response.
Which of the following statements about vesicular membrane fusion is false:
a. Membrane fusion does not always immediately follow vesicle docking
b. The hydrophilic surfaces of membranes have water molecules associated with them that must be displaced before vesicle fusion can occur
c. The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion.
d. The interactions of the v-SNAREs and the t-SNAREs pull the vesicle membrane and the target organelle membrane together so that their lipids can intermix
The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion.
A patient suffers from atherosclerosis due to high LDL in their bloodstream. Upon investigation, their doctor finds that they have a mutation in the cytoplasmic domain of LDL receptors. Which of the following can explain the disease condition:
a. These LDL receptors can no longer bind to LDL particles
b. These LDL receptors can no longer bind to AP2 complexes
c. These LDL receptors are being targeted to the lysosome for degradation
d. LDL receptors cannot be translocated to the PM
e. b, c, and d
b, c, and d
A protein undergoes multiple rounds of ATP hydrolysis while it translocates a completely synthesized protein across the ER membrane. What is this protein?
a. Sec 61
b. SRP
c. BiP
d. SR
BiP
What is the function of RanGAP in relation to nuclear import and export?
a. Bind importins/exportins and bring them through the nuclear pore complex
b. Attach GTP to Ran
c. Maintain a gradient of GTP/GDP bound Ran
d. Bind cargo proteins
Maintain a gradient of GTP/GDP bound Ran
Which of the statements are CORRECT regarding N-linked glycosylation?
a. The addition of an N-linked oligosaccharide to a protein occurs in the cytoplasm
b. N-linked oligosaccharides are transferred to a protein as a 14 sugar precursor molecule in the endoplasmic reticulum
c. N-linked oligosaccharides are added to a bipartite amino acid sequence rich in lysine residues
d. The initial removal of two terminal glucose residues and a mannose residue serves as a regulatory checkpoint and indicates the protein is ready to be transported to the cls- Golgi complex
N-linked oligosaccharides are transferred to a protein as a 14 sugar precursor molecule in the endoplasmic reticulum
Using a mutant analysis, you create three temperature sensitive mutants, mutant A, mutant B and mutant C. In mutant A, proteins accumulate in the lysosome. In mutant B, proteins remain bound to receptors on the plasma membrane. In mutant C, proteins remain in the early endosome. In an A/B double mutant, proteins remain bound to receptors on the plasma membrane. In an A/C double mutant, proteins accumulate in the early endosome. Based on what we know about endocytosis, what is the epistatic order of genes?
Gene B (plasma membrane) → Gene C (early endosome)→ Gene A (lysosome)
In a epithelial cell, polarized localization of newly synthesized membrane proteins is ensured by the following mechanism(s):
Sorting of proteins into distinct apical and basolateral secretory vesicles