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Biochemistry
1. Molecular biologists studying signal transduction apply an agent to human cells that activates G-proteindependent phospholipase C. Which of the following intracellular substances is most likely to increase immediately after exposure to this agent?
A. Ca2+
B. cAMP
C. cGMP
D. Cl·
E. mRNA
F. NO
2. Researchers studying molecular biology observe a eukaryotic cell via electron microscopy. During interphase of the cell cycle, they notice 10-nm thick chromatin fibers with a “beads on a string” appearance. These chromatin fibers are extracted and treated with an endonuclease, which preferentially cleaves the “string” portions of the chromatin. Further evaluation reveals that the “beads” are composed of DNA wrapped around a core of proteins. Which of the following proteins is most likely found outside this core and promotes chromatin compaction?
A. Histone H1
B. Histone H3
C. Histone H4
D. Small nuclear ribonucleoprotein
E. Type II topoisomerase
F. Ubiquitin
3. A 47-year-old homeless man comes to the emergency department due to a “pins-and-needles” sensation in his legs. He also has painful lesions on his lips and comers of his mouth. He has had no loss of consciousness, nausea, vomiting, or diplopia. The patient drinks alcohol heavily on a daily basis and has a history of intravenous heroin use. On physical examination, he appears unkempt and ill appearing. Temperature is 36.8 C (98.2 F), blood pressure is 146/90 mm Hg, and pulse is 106/min. He has glossitis and angular stomatitis. Abdominal examination reveals hepatomegaly. Laboratory evaluation shows very low urinary riboflavin excretion. Activity of which of the following enzymes is most likely directly impaired in this patient?
A. Fumarase
B. Glucose6-phosphate dehydrogenase
C. HMG-CoA reductase
D. lsocitrate dehydrogenase
E. Malate dehydrogenase
F. Succinate dehydrogenase
G. Succinate thiokinase