USABO Open Exam 2013 with complete answers

Which statement is true about enzymes? Enzymes A. Are made up of a base containing nitrogen, phosphate, and ribose. B. Have activity that is independent of temperature and pH. C. Lose some or all of their normal activity when their 3-D structure is disrupted. D. Provide the activation energy needed to activate a reaction. E. Work once only and then are destroyed. correct answersC. Lose some or all of their normal activity when their 3-D structure is disrupted. You have a multicellular organism that reproduces asexually by fission. When you excise a ~10,000 cell portion of its body, both the original organism and the excised portion grow into fully formed, healthy organisms. You take one of the offspring and repeat the procedure for one hundred and twenty-three generations. Each time, the resulting organisms are healthy. What must be true of the nuclei of this species? A. The cells contain plasmids. B. The cells have multiple forms of DNA polymerase. C. The cells have the majority of their genome stored in circular DNA. D. The cells contain active telomerase. E. The cells contain active fissonase. correct answersD. The cells contain active telomerase. Which of the following correctly describes how the lifespan of a protein is regulated? A. The part of the sequence coded for by the UTR tags it for destruction. B. Giant protein complexes called ubiquitins destroy proteins after they have remained in the cell for a certain time. C. Proteins are methylated over time; heavily methylated proteins are destroyed by proteasomes.