USABO Open Exam 2024 with Verified Answers Graded A.

USABO Open Exam 2024 with Verified Answers Graded A. 1. What best describes a nucleosome? A. Region in bacterial cells where DNA is located. B. DNA wrapped around 8 histone cores. C. RNA with protein bound. D. A region in the nucleus where ribosomes are assembled. E. The space between the layers of the nuclear membrane. 2. You observe fly cells that are undergoing meiosis and treat them with a drug that inhibits the separation of parental homologs. At which stage of meiosis do cells treated with this drug become arrested? A. Prophase I B. Metaphase I C. Anaphase I D. Telophase I E. Prophase II AB. Metaphase II AC. Anaphase II AD. Telophase II 3. Psoriasis is a skin disorder that is caused by the increased proliferation of skin cells and results in red, itchy skin. Skin cells from a mouse model for this disease are isolated and cultured in a plate containing a drug that promotes the supercoiling of DNA. Which enzyme does this drug inhibit? A. DNA polymerase. B. Helicase. C. Topoisomerase. D. Primase. E. DNase. 4. Which phase of the cell cycle do cells treated with the drug specified in Question 3 become arrested? A. G0 phase. B. G1 Phase. C. G2 phase. D. M phase. E. S phase. Page 2 5. A liquid culture of yeast was grown under anaerobic conditions but then had a significant quantity of alcohol dehydrogenase inhibitor added to the medium. Which of the following would best describe the effect on glycolysis due to the presence of the inhibitor? A. Glycolysis would continue with no change in catabolic efficiency. B. Glycolysis would continue with higher catabolic efficiency. C. Glycolysis would continue with lower catabolic efficiency and pyruvate would be further broken down through the Krebs cycle. D. Glycolysis would continue with lower catabolic efficiency and the cells would start to excrete pyruvate instead of alcohol. E. The rate of glycolysis would slow to a complete stop. 6. C-Myc is a transcription factor that recognizes DNA bases using hydrophobic interactions. By binding to specific DNA sequences, c-Myc can encourage cell division. In order to halt cell division, what mutations can one make to c-Myc? A. Change the nucleotides in the recognition site sequence from GCATTG to CGTAAC. B. Change the nucleotides in the recognition site sequence from GCATTG to TATGGT. C. Change the amino acids in the recognition site sequence from GVVLIA to AFFLLP. D. Change the amino acids in the recognition site sequence from GVVLIA to FAFIIL. E. Change the amino acids in the recognition site sequence from GVVLIA to TRKESE. 7. A replication inhibitor is added to stem cells in the middle of DNA replication. At what phase of the cell cycle would these cells remain? A. Mitosis. B. G0 phase. C. G1 phase. D. S phase. E. G2 phase.