Exam 15: Intracellular Compartments and Protein Transport

Your friend has just joined a lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles.He wants to start designing some experiments but was not listening carefully when he was told about the molecular defect of this cell line.He is too embarrassed to ask and comes to you for help.He does recall that this cell line forms coated pits but vesicle budding and the removal of coat proteins don't happen.Which of the following proteins might be lacking in this cell line?

What is the role of the nuclear localization sequence in a nuclear protein?

Signal sequences that direct proteins to the correct compartment are

Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP.What is the most likely effect of this drug on nuclear transport?

What would happen in each of the following cases? Assume in each case that the protein involved is a soluble protein, not a membrane protein. A.You add a signal sequence (for the ER) to the N-terminal end of a normally cytosolic protein. B.You change the hydrophobic amino acids in an ER signal sequence into charged amino acids. C.You change the hydrophobic amino acids in an ER signal sequence into other hydrophobic amino acids. D.You move the N-terminal ER signal sequence to the C-terminal end of the protein.

Which of the following statements about disulfide bond formation is FALSE?

Which of the following statements about a protein in the lumen of the ER is FALSE?

Molecules to be packaged into vesicles for transport are selected by

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; use each word or phrase only once. amino acid sequence Golgi apparatus sorting signal endoplasmic reticulum plasma membrane transport vesicles folded protein translocators unfolded Plasma membrane proteins are inserted into the membrane in the __________.The address information for protein sorting in a eukaryotic cell is contained in the __________ of the proteins.Proteins enter the nucleus in their __________ form.Proteins that remain in the cytosol do not contain a __________.Proteins are transported into the Golgi apparatus via __________.The proteins transported into the endoplasmic reticulum by __________ are in their __________form.

Figure 15-22 shows the organization of a protein that normally resides in the plasma membrane.The boxes labeled 1 and 2 represent membrane-spanning sequences and the arrow represents a site of action of signal peptidase.Given this diagram, which of the following statements must be TRUE? Figure 15-22

You have created a green fluorescent protein (GFP) fusion to a protein that is normally secreted from yeast cells.Because you have learned about the use of temperature-sensitive mutations in yeast to study protein and vesicle transport, you obtain three mutant yeast strains, each defective in some aspect of the protein secretory process.Being a good scientist, you of course also obtain a wild-type control strain.You decide to examine the fate of your GFP fusion protein in these various yeast strains and engineer the mutant strains to express your GFP fusion protein.However, in your excitement to do the experiment, you realize that you did not label any of the mutant yeast strains and no longer know which strain is defective in what process.You end up numbering your strains with the numbers 1 to 4, and then you carry out the experiment anyway, obtaining the results shown in Figure 15-17 (the black dots represent your GFP fusion protein). Figure 15-17 Name the process that is defective in each of these strains.Remember that one of these strains is your wild-type control.

Proteins that are fully translated in the cytosol and lack a sorting signal will end up in the

An individual transport vesicle

A gene regulatory protein, A, contains a typical nuclear localization signal but surprisingly is usually found in the cytosol.When the cell is exposed to hormones, protein A moves from the cytosol into the nucleus, where it turns on genes involved in cell division.When you purify protein A from cells that have not been treated with hormones, you find that protein B is always complexed with it.To determine the function of protein B, you engineer cells lacking the gene for protein B.You compare normal and defective cells by using differential centrifugation to separate the nuclear fraction from the cytoplasmic fraction, and then separating the proteins in these fractions by gel electrophoresis.You identify the presence of protein A and protein B by looking for their characteristic bands on the gel.The gel you run is shown in Figure 15-4. Figure 15-4 On the basis of these results, what is the function of protein B? Explain your conclusion and propose a mechanism for how protein B works.

Different glycoproteins can have a diverse array of oligosaccharides.Which of the statements below about this diversity is TRUE?