NAME ___________________________________BIOLOGY 052, SECTION 006 EXAM 2 SPRING 2008+ PRINT YOUR NAME AT THE TOP OF EVERY PAGE.+ USE A PEN, NOT PENCIL.+ SIGN THE HONOR PLEDGE AT THE END OF THE EXAM.+ USE ONLY THE SPACE PROVIDED FOR YOUR ANSWER.+ QUESTIONS WILL BE GRADED ON BOTH HOW CORRECT AND HOW COMPLETE YOUR ANSWER IS.1. (20 points) Match the definition below with its term from the list above.axoneme flagellum pseudopodiumcilium lamellipodium Rho protein familyfilopodium myofibril Arp proteinkinesin vimentin dyneintubulin heterodimer desmin dynamic instabilityneurofilament Rho Listeriakeratin contraction myosin IIfilamin catastrophin microtubule-associated protein(a) A group of closely related monomeric GTPases that includes Cdc42, Rac, and Rho.Rho protein family(b) Bundle of microtubules that forms the core of a cilium or flagellum in a eukaryotic cell and is responsible for their movements.axoneme(c) Long, highly organized bundle of actin, myosin, and other proteins in the cytoplasm of muscle cells that contracts by a sliding-filament mechanism.myofibril(d) Flattened, two-dimensional protrusion of membrane, supported by a meshwork of actin filaments, that is extended from the leading edge of crawling epithelial cells, fibroblasts, and some neurons.lamellipodium(e) Long, hairlike protrusion from the surface of a eukaryotic cell whose undulations drive the cell through a fluid medium.flagellumf) Class of proteins that mediate the depolymerization of microtubules from their plus end.catastrophin(g) Intermediate filament protein that is predominantly expressed in epithelial tissue and gives mechanical strength to skin.keratin(h) A protein that induces the nucleation of new actin filaments in the lamellipodia of motile cells.Arp protein(i) Microtubule-based motor that transport cargos to the minus ends.Dynein(j) Small G protein that activates cell contraction at the trailing edge of motile cells.Rho2. (10 points) One important role of Fas and Fas ligand is to mediate the elimination of tumor cells by killer lymphocytes. In a study of 35 primary lung and colon tumors, half the tumors were found to have amplified and overexpressed a gene for a secreted protein that binds to Fas ligand. How do you supposethat overexpression of this protein might contribute to the survival of these tumor cells? Explain your reasoning.Overexpression of a Fas ligand would protect these cells from exogenously-induced apoptosis. (5 pts)The secreted protein would prevent the Fas ligand from binding to Fas on the tumor cell surface, thereby insulating them from the death-inducing interactions with killer lymphocytes. (5 pts)3. (10 points) The drugs taxol, extracted from the bard of yew trees, and colchicine, an alkaloid from autumn crocus, have opposite effects. Taxol binds tightly to microtubules and stabilizes them. When added to cells, it causes much of the free tubulin to assemble into microtubules. In contrast, colchicine prevents microtubule formation. Taxol and colchicine are equally toxic to dividing cells, and both are used as anticancer drugs. Based on your knowledge of microtubule dynamics, explain why these drugs are toxic to dividing cells despite their opposite modes of action.As cells enter mitosis, cells reorganize their microtubules to build a spindle from the interphase microtubule array and this requires dynamic instability. (5 points) Inhibition of dynamic instability will also interfere with microtubule capture by kinetochores, thus setting off the mitotic checkpoint and leading to apoptosis. (5 points)4. 10 points) Filamin is an actin-binding protein that cross-links actin filaments at roughly right-angles to produce a viscous gel that is required for cells to extend sheet-like lamellipodia. Why is the loss of filamin in melanoma cells bad news for the melanoma cells, but good news for the patient?Lamellipodia mediate protrusion of the leading edge - without it cellular migration is inhibited (5 points) This inhibition of migration decreases the likelihood of metastasis, and improves the prognosis for cancer patients (5 pts).5. (20 points) Match the definition below with its term from the list above.adaptation intracellular signaling protein positive feedback loopadaptor ion-channel-coupled receptor MAP kinase cascadeprotein kinase A contact-dependent signaling protein kinase Cendocrine cell monomeric GTPase protein phosphatasemitogen enzyme-coupled receptor receptorscaffold protein negative feedback loop paracrine signalingneurotransmitter second messenger GPCRnitric oxide (NO) serine/threonine kinase NO synthase (NOS)signaling cascade nuclear receptor superfamily GTP-binding proteinsteroid hormone phosphorylation tyrosine kinasehormone phospholipase C adenylyl cyclase(a) Enzyme that cleaves inositol phospholipids into diacylglycerol (DAG) and inositol triphosphate (IP3).Phospholipase C(b) Short-range cell-cell communication via secreted local mediators that act on adjacent cells.paracrine signaling(c) A signal relay chain involving multiple protein kinases, each of which is activated by phosphorylation and then phosphorylates the next protein kinase in the sequence.MAP kinase cascade(d) Hydrophobic signaling molecule with a characteristic four-ringed structure derived from cholesterol.steroid hormone(e) Class of small molecule that is formed in the cytosol, or released into it, in response to an extracellular signal that helps to relay the signal to the interior of the cell.Second messenger(f) Specialized animal cell that secretes a hormone into the bloodstream.Endocrine cell(g) Enzyme that transfers the terminal phosphate group of ATP to a specific amino acid of a target protein.kinase(h) Cell-cell communication in which the signal molecule remains bound to the signaling cell and only influences cells that physically touch it.Contact-dependent signaling(i) Small signal molecule secreted by the presynaptic nerve cell at a chemical synapse to relay the signalto the postsynaptic cell.neurotransmitter(j) Enzyme that catalyzes the conversion of ATP into cAMP.Adenylyl cyclase6. (10 points) A single amino acid change in Ras eliminates its ability to hydrolyze GTP. Roughly 30% of human cancers have this mutation in Ras. You have just identified a small molecule inhibitor that prevents dimerization of a receptor tyrosine kinase that signals via Ras. Would you expect this small molecule inhibitor to be useful as a drug to treat cancers that that express this
View Full Document
Unlocking...