Test Questions - Biology PDF

1\. What is the major way by which the monomeric G protein Ras is activated in receptor tyrosine kinase signaling? A. By activation with Ras-GAP\ B. By activation with Ras-GEF\ C. By activation with Ras-Gα\ D. By activation with Ras-Gβγ Answer: B 2\. \_\_\_\_ is a cytoplasmic tyrosine kinase pres...

1\. What is the major way by which the monomeric G protein Ras is activated in receptor tyrosine kinase signaling? A. By activation with Ras-GAP\ B. By activation with Ras-GEF\ C. By activation with Ras-Gα\ D. By activation with Ras-Gβγ Answer: B 2\. \_\_\_\_ is a cytoplasmic tyrosine kinase present at cell-extracellular matrix (ECM) junctions in association with the cytoplasmic tails of integrins. A. Rho\ B. FAK\ C. STAT Answer: B 3\. Propose specific mutations in the gene for the regulatory subunit of cyclic-AMP-dependent protein kinase (PKA) that could lead to either a permanently active or a permanently inactive PKA. Answer: PKA would be permanently active if the regulatory subunits cannot bind the catalytic subunits. PKA would be permanently inactive if the regulatory subunits bind the catalytic subunits and cannot bind or respond to cyclic AMP. 4\. Ryanodine and IP3 receptors are found on \_\_\_\_\_\_\_\_ membranes, whereas receptors EGFR and TGFβR are localized on \_\_\_\_\_\_\_\_ membranes. A. Endoplasmic reticulum; plasma\ B. Plasma; intracellular\ C. Mitochondrial; nuclear\ D. Outer; inner Answer: A 5\. The cytokine interleukin-2 binds to its catalytic receptor on a T lymphocyte. In response, which of the following will take place? A. The activity of adenylyl cyclases will increase\ B. The calcium concentration at the endoplasmic membrane will decrease\ C. The level of phosphotyrosines on specific proteins will increase\ D. Ras will move into the nucleus Answer: C 6\. \_\_\_\_ are examples of phosphoinositide-derived messengers. A. PLCβ and PI3K\ B. cAMP and cGMP\ C. DAG and IP3\ D. Nitric oxide and Ca2+ Answer: C 7\. Each RTK can activate diverse downstream pathways because \_\_\_\_. A. Activated RTKs directly phosphorylate tyrosine residues on many different substrates\ B. The phosphorylated tyrosine(s) in the cytoplasmic domain of RTKs can interact with different adaptor proteins, initiating different signaling pathways\ C. RTKs can phosphorylate Tyr and Ser/Thr in adaptor proteins, generating diverse signaling cascades\ D. RTKs function as dimers or monomers upon ligand binding, with each state leading to different pathways Answer: B 8\. L-Arginine is a nutritional supplement that is used to ease cardiac problems by promoting vasodilation. What is the mechanism that accounts for this beneficial effect? Answer: L-Arginine serves as a substrate for nitric oxide (NO) production. NO promotes vasodilation by relaxing smooth muscle cells in arteries, increasing blood flow and reducing blood pressure. cGMP phosphodiesterase would reduce this effect by breaking down cGMP, which would diminish vasodilation. 9\. In cells that lack Ras-specific GAP activity, what changes would you expect to see in Ras activity in the absence and presence of extracellular signals? Answer: Without Ras-specific GAP activity, there would be an increase in GTP-bound Ras, leading to sustained signaling in both the absence and presence of extracellular signals. 10\. A gene encoding a mutant tyrosine kinase receptor (RTK) is introduced into cells that also express normal copies of the RTK. If the mutant RTK is expressed at higher levels, what would be the consequences if (a) the mutant RTK lacks an extracellular domain, and (b) it lacks an intracellular domain? Answer: (a) Without the extracellular domain, the RTK will be inactive since it cannot bind ligands. (b) Without the intracellular domain, the RTK will also be inactive and may act as a dominant-negative by sequestering ligands from binding to functional receptors. 11\. A cell line with a constitutively active Ras protein requires which condition to turn off signaling? A. Addition of a drug that inhibits the RTK\ B. Addition of a drug that increases the interaction of protein Y and Ras\ C. Addition of a drug that blocks protein Y from interacting with its target\ D. Addition of a drug that increases the activity of protein Y Answer: C 12\. When insulin binds to the insulin receptor (IR), it initiates downstream events that include \_\_\_\_\_. A. The formation of a disulfide bond between the IR chains\ B. The autophosphorylation of Ser or Thr residues on the IR cytoplasmic domains\ C. The binding of the docking protein IRS-1 to the activated IR\ D. The recruitment of cytoplasmic kinase SRC to the activated IR Answer: C 13\. What type of feedback occurs if MEK activates (a) a RAS-specific GEF or (b) a RAS-specific GAP? Answer: (a) Activation of a RAS-specific GEF by MEK provides positive feedback, increasing RAS-GTP levels and MEK activity downstream. (b) Activation of a RAS-specific GAP provides negative feedback, reducing RAS-GTP and thus MEK activity downstream. 14\. The growth factor SuperX binds an RTK, leading to uncontrolled proliferation of cultured chicken cells. Which mutation would promote this proliferation? A. Destroys the kinase activity of the RTK\ B. Promotes the monomer state of the SuperX-bound RTK\ C. Prevents the endocytosis of the RTK\ D. Prevents the binding of SuperX to the receptor Answer: C 15\. In human cancer, mutations in RAS genes at specific codons abolish RAS-GTP hydrolysis. What effect would such mutations have on signaling pathways downstream of RAS? A. Downstream pathways would be downregulated\ B. Downstream pathways would be transiently activated and then inactivated\ C. Downstream pathways would be transiently activated\ D. Downstream pathways would be constitutively activated Answer: D 16\. If cells were exposed to an antibody that specifically binds the extracellular domain of an RTK, what is the expected outcome? A. The RTK would be inactivated\ B. The RTK would be activated\ C. The RTK would be exocytosed\ D. The RTK would be unaffected Answer: B 17\. Lithium is used to treat manic-depressive illness, which may involve overproduction of IP3 and DAG. Lithium most likely functions to inhibit \_\_\_\_\_. A. Adenylyl cyclase activity\ B. Gαs protein function\ C. Phospholipase C activity\ D. PKA activity Answer: C 18\. A cell-surface receptor with either intrinsic enzymatic activity or association with an intracellular enzyme is a \_\_\_\_\_. A. Receptor tyrosine kinase\ B. Tyrosine-kinase-associated receptor\ C. Protein kinase A\ D. Catalytic receptor Answer: D 19\. When insulin binds to an insulin receptor on an adipocyte, which signaling process occurs? A. Activation of protein kinase C to phosphorylate substrates\ B. Tyr phosphorylation of the docking protein IRS\ C. G protein activation of second messenger production\ D. Translocation of the insulin receptor to the cell's nucleus Answer: B 20\. A cell-surface receptor that is activated by ligand binding and adds phosphates from ATP to tyrosine side chains in its own cytoplasmic domain is a \_\_\_\_\_. A. Cytoplasmic tyrosine kinase\ B. Receptor tyrosine kinase (RTK)\ C. GPCR\ D. Tyrosine-kinase-associated receptor Answer: B 21\. Which pathway is unique to GPCR signal termination? A. Receptor phosphorylation\ B. Binding to arrestins\ C. Endocytosis\ D. Receptor degradation at the plasma membrane Answer: B 22\. A kinase that phosphorylates inositol phospholipids and is activated by a cell surface receptor is called \_\_\_\_\_. A. Phospholipase C\ B. Phosphoinositide 3-kinase (PI3-kinase)\ C. Rac\ D. Ras Answer: B 23\. UZO1 is a scaffolding protein that binds to pTyr, PI(3,4,5)P3 (PIP3), and proline-rich domains. Which domains recognize these structures? A. 1=SH2; 2=PH; 3=SH3\ B. 1=SH3; 2=PH; 3=SH2\ C. 1=SH3, 2=PTB; 3=PH\ D. 1=SH2; 2=PTB; 3=PH Answer: A 24\. UZO1 is a scaffolding protein that binds to pTyr, PI(3,4,5)P3 (PIP3), and proline-rich domains. Which domains recognize these structures? A. 1=SH2; 2=PH; 3=SH3\ B. 1=SH3; 2=PH; 3=SH2\ C. 1=SH3, 2=PTB; 3=PH\ D. 1=SH2; 2=PTB; 3=PH Answer: A