MCB 2210 FALL 2021 PROBLEM SET 3 1. A given protein is regulated by a protein kinase and a protein phosphatase, and is active when phosphorylated. Which would you expect to INCREASE the protein’s activity? a. Expression of a mutant, nonfunctional kinase that blocks the activity of the cell’s normal kinases (a “dominant-negative” kinase) b. Expression of a mutant, nonfunctional phosphatase that blocks the activity of the cell’s normal phosphatases (a dominant-negative phosphatase) c. Expression of a mutant, hyperactive phosphatase. d. a and b are correct. e. b and c are correct. 2. Which statement about phosphorylation is correct? a. The addition of phosphate from ATP ALWAYS turns the target protein “on” while their removal turns the protein “off” b. The negative charge of the phosphate groups can attract positively charged amino acid side chains of the protein and therefore alter the overall shape of the protein and its binding sites. c. The addition and removal of phosphate groups from proteins occurs in response to signals that specify a change in the state of a cell. d. Both b and c are correct. Phosphorylation just changes state of target- for ex., an enzyme could be turned on or off, depending on the specific enzyme in question e. a, b, and c are correct 3. Ras is a small G protein that regulates cell proliferation in response to growth factors. When Ras is in its active form, cells proliferate. The activity of Ras is carefully regulated by two other proteins: Ras GEF (guanine nucleotide exchange factor) which stimulates binding of GTP by Ras, and Ras GAP (GTPase activating protein) which stimulates GTP hydrolysis by Ras. The activities of these regulatory proteins are, in turn, also regulated. Ras activity stimulates cell proliferation. Which of the following changes in GAP and GEF proteins might cause a cell to increase proliferation? a. A nonfunctional GAP. b. A permanently active GAP. c. A nonfunctional GEF. d. A permanently active GEF. e. a and d are true. 4. Ran's role in regulating nucleocytoplasmic transport is based on a mechanism in which the cell maintains a ______ nuclear concentration and a very low cytoplasmic concentration of ______. a. low Ran-GDP, Ran-GTP b. high Ran-GDP, Ran-GTP c. high Ran-GTP, Ran-GTP d. a and c5. Of these five steps listed, what is the FOURTH step in making a nuclear protein? a. The DNA is transcribed. b. The mRNA is transported through the nuclear pore to the cytoplasm. c. The protein moves through the pore into the nucleus. d. The protein folds. e. The mRNA is translated. 6. You!have isolated the gene for a protein called nuculin that normally is transported into the nucleus. You locate in the gene the portion of the coding sequence that codes for the nuclear localization signal (NLS) and engineer it so that a positively charged amino acid in the nuclear localization signal is replaced by a nonpolar amino acid, a change that disrupts the NLS and renders it nonfunctional. You then insert the gene into cells and observe where nuculin goes after its synthesis. What is the effect, if any? a. Nuculin will no longer be translated by the cell.! b. Nuculin will move into the ER.! c. Nuculin will move in to the nucleus as it usually does. d. Nuculin will localize to mitochondria. e. None of the above is a correct statement. 7. Which of the following is FALSE about nuclear localization signal and nuclear export signal? a. Nuclear export receptors recognize the NES to be brought back to the cytoplasm. b. Nuclear import receptors recognize the NLS to be brought into the nucleus. c. The NES and NLS have similar sequences and function and work in opposite directions. d. The NES and NLS have similar sequences and function and work in the same direction. e. Movement is regulated through the nuclear pore complex with the aid of G-proteins. 8. Which of the following is not a function of the nuclear lamina? a. It provides mechanical support for the nuclear envelope. b. It is a point of attachment for the enzymes that synthesize histone. c. It serves as an attachment site for chromatin fibers at the nuclear periphery. d. It binds to ribosomes that are conducting protein synthesis. e. b and d9. You isolated a protein and tagged it with a fluorescent probe. You microinjected the protein into the cytoplasm of a Xenopus oocyte and observed the localization of the protein as shown in the diagram. The stippled (dotted) region is the area that appears fluorescent. What is the correct interpretation of the experiment? a. Tail is necessary but not sufficient for the protein to be transported into the nucleus. b. Head is necessary and sufficient for the protein to be transported into the nucleus. c. The tail is neither necessary nor sufficient for import into the nucleus. d. Neither tail nor head alone is sufficient for import into the nucleus. e. a and d 10. Which of the following things can be moved either in, out, or in both directions through nuclear pores? a. mRNAs b. snRNAs c. ribosomal subunits d. tRNAs e. all of the above 11. What happens to Ran-GTP after it has been transported to the cytoplasm bound to an importin? a. Bound GTP is hydrolyzed to GDP. b. Bound GTP is hydrolyzed to GMP. c. Ran-GDP is released from the importin. d. Ran-GTP binds to the importin subunit. e. a and c are correct. 12. After transport into the nuclear compartment, what interacts with the importin-cargo complex and what effect does it have on the complex? a. Ran-GTP, causes the importin-cargo complex to disassemble b. Ran-GDP, causes the importin-cargo complex to disassemble. c. Ran-GTP, causes the importin-cargo complex to be destroyed. d. Ran-GDP, causes the importin-cargo complex to be destroyed. e. Ran-GTP, causes the importin-cargo complex to be stabilized13. Which protein serves as an accessory protein that typically resides in the cytoplasm where it promotes the conversion via hydrolysis of Ran-GTP to Ran-GDP? a. Ran-GTP b. Ran-GEF c. Ran-GAP d. Ran-GDP e. Ran-GMP 14. Which of the following correctly describes components that interact to successfully complete the import of cargo proteins from the cytoplasm to the nucleus? a. cargo—importin—Ran-GTP complex b. cargo—exportin—Ran-GDP complex c. cargo—exportin—Ran-GTP complex d. cargo—importin—Ran-GDP complex e. None are correct. 15. What would you expect to happen if you massively overexpressed a very active RanGEF in the