BL 424 Test 3 2010 150 pts name Multiple choice have one choice each and are worth 3 points. 1. The plasma membrane functions as a a. selective barrier to the passage of molecules. b. sensor through which the cell receives signals from the environment. c. site for uptake of macromolecules into the cell. 2. Integrins are: a. transmembrane proteins b. peripheral membrane proteins c. components of the extracellular matrix d. components of the desmosome 3. Mammalian erythrocytes (red blood cells) are particularly useful for plasma membrane studies: a. they have few peripheral proteins. b. they have only one membrane, the plasma membrane. c. their plasma membrane is not associated with a cytoskeleton. 4. Membrane proteins are able to move a. from the inner to the outer surface of a membrane. b. laterally within the plane of a membrane. c. from apical to basal surfaces of intestinal epithelial cells. d. only if attached to microtubules or microfilaments. 5. Neurotransmitters act by binding to receptors that are a. ligand-gated ion channels b. G protein-linked receptors c. tyrosine-kinase receptors d. both a and b 6. The function of gap junctions is to a. hold epithelia together. b. provide direct communication between cells. c. seal the space between cells. 7. The first step in polypeptide growth factor pathway activation is a. Ras activation. b. receptor phosphorylation. c. receptor dimerization. d. binding of SH2-containing proteins. 8. Cholera toxin inhibits the ability of the Gs α subunit to split GTP. The resulting effect on adenylyl cyclase activity is to: a. increase activity b. decrease activity c. degrade adenylyl cyclase molecules d. ubiquitinate the adenylyl cyclase
2 9. The major (if not the only) function of camp in animal cells is to activate a. adenylyl cyclase. b. tyrosine kinases c. protein kinase C. d. protein kinase A. 10. Drugs that inhibit farnesylation inhibit Ras function because Ras connot, without its farnesyl group, a. split GTP b. bind to Raf c. bind src d. bind to the plasma membrane 11. MAP kinase signal cascades are often organized into functional groups or cassettes by a. scaffold proteins. b. binding of SH2 domains to each other. c. lipid rafts. d. binding MAP kinase-responsive genes. 12. If the amount of DNA in an egg or sperm is n, then the amount of DNA in an epithelial G 2 cell is usually: a. n. b. 2n. c. 4n. d. 8n. 13. Growth-factor stimulation of the Ras/Rat/ERK pathway initially stimulates the synthesis of cyclin a. A. b. B. c. C. d. D. 14. Entry into mitosis occurs because a. cyclin is destroyed at the beginning of mitosis. b. cyclin is phosphorylated at the beginning of mitosis. c. sufficient cyclin-dependent kinase is synthesized to trigger mitosis. d. cyclin binds to a protein kinase and activates it. 15. The RNA viruses that most commonly pick up cellular oncogenes are the a. adenoviruses. b. retroviruses. c. papillomaviruses. d. HIV viruses 16. In meiosis I, sister chromatids a. go to opposite poles. b. go to the same poles. c. have kinetochores facing in opposite directions. d. synapse with each other during the zygotene stage. 17. Cancer is usually caused by a. a cancer virus. b. an inherited oncogene. c. the stepwise breakdown of normal cell regulatory processes. d. X-rays. 18. The dramatic increase in cancer incidence with age suggests that a. cancer is caused by old age. b. genetic factors are not involved. c. cancer arises primarily in differentiated, nondividing tissues. d. cancer develops as a consequence of multiple abnormalities that accumulate over many years. 19. Malignant colon cancers are usually the result of a. inherited mutant oncogenes. b. inherited mutant tumor suppressor genes. c. somatic mutation of an oncogene or tumor suppressor gene. d. accumulated damage to multiple oncogenes and tumor suppressor genes.
20. (3) The ras gene is mutant in 50% or more of some types of human cancer. When ras is mutant, it typically remains active in mitogenic signal transduction because it is unable to 3 21. (12 pts) Enzyme matching: one choice each; choices are used only once; there are extra choices. ubiquitin ligase a. extends the ends of linear chromosomal DNA protein kinase b. transcription factor cyclin c. adds phosphates to proteins APC/C d. adds ubiquitin to cause protein degradation telomerase e. adds ubiquitin to stabilize proteins fos and jun f. short-lived protein g. results in separation of sister chromatids 22. (12 pts) Matching diseases. One choice each, from protein, and from role of normal protein Retinoblastoma a. c-myc 1. Endocytosis Cystic fibrosis b. Rb protein 2. Transcription factor- differentiation Acute promyelocytic leukemia c. LDL receptor 3. Tumor suppressor Charcot-Marie Tooth syndrome d. CFTR 4. Cl- channel, ABC transporter Familial hypercholesterolemia e. PML/RAR 5. Gap junction protein Burkitt s lymphoma f. connexin 6. Transcription factor - proliferation 23. (4 pts) Extracellular matrix. Aggrecan contains 100 chains of chondroitin sulfate bound to a core protein of 250 kd, for a total molecular weight of 3000 kd. What percentage of the total is protein? ; What is the molecular weight of each chondroitin sulfate chain? 24. (8 pts) Matching cell walls and extracellular matrix. For each structure, indicate which component(s) are present Choices may be used once, more than once or not at all. Gram-negative cell wall a. cellulose Gram-positive cell wall b. collagen Plant cell wall c. peptidoglycan animal cell Extracellular matrix d. proteoglycan e. outer phospholipid membrane f. hyaluronic acid g. pectin, hemicelluloses 25. (5 pts) How might a proto-oncogene be converted into an oncogene without a change or truncation of its coding sequence? Explain two ways this might occur. Specific examples may be helpful. 26. (4 pts) Phosphatidyl inositol is found exclusively on one side of the plasma membrane. Which side? (cytoplasmic or extracellular face), and what is the significance/ functional value of this location? Explain concisely.
4 27. (10 pts) The Na+ gradient across the plasma membrane of eukaryotic cells represents a source of usable potential energy. a. (4) How do cells establish this gradient? On which side of the membrane is Na+ higher? Be specific as to ions and energy involvement. b. (4) What cellular functions do eukaryotic cells perform utilizing this energy of the transmembrane Na+ gradient? Give two examples. c. (2) In prokaryotic cells, what ion gradient accomplishes this same general function? 28. (10 pts) Regulation of the eukaryotic cell cycle involves a factor termed MPF that is composed of two proteins termed and. (4 pts) Briefly explain the following experimental observations: a. (3) when an abnormal, indestructible form of mitotic cyclin is introduced into cells, they enter into mitosis but cannot emerge from it and reenter G1 phase. b. (3) Mutations that inactivate the main protein phosphatase used to catalyze protein dephosphorylations cause a long delay in reconstruction of the nuclear envelope that normally takes place at the end of mitosis. 29. (4 pts) A mutation in an epithelial cell leads to the expression of an integrin with a deleted cytoplasmic domain. How would this mutation affect adhesion of the epithelial cell to the basal lamina? Explain concisely.
30. (4 pts) Briefly explain two advantages of Saccharomyces cerevisiae as an experimental model for studying regulation of the cell cycle. 5 31. (10 pts) One way to assess distribution of cells between portions of the cell cycle is to measure the amount of DNA per cell. Flow cytometry with fluorescence-activated cell sorter (FACS) quantifies the fluorescence of individual cells in a population using dyes that bind double helical DNA. a. (2) Fig. 1 shows a plot of cell number versus fluorescence for an exponentially growing HeLa cell population. Based on this plot, indicate the relative distribution of cells in the various phases of the cell cycle? Draw and label on the figure. b. (8) Sketch expected FACS plots if cells were arrested in each of the cell-cycle phases, namely G 0, G 1, S, and M. Draw new plots and clearly label. 32. (6 pts) In referring to the war on cancer, J. Michael Bishop, Nobel Laureate for his work with oncogenes, quoted a line from the Pogo comic strip: We have met the enemy and he is us. Explain briefly why this quotation is appropriate.