Metabolism & Bioenergetics MCAT Practice Question
A 34-year-old woman with type 2 diabetes mellitus presents for routine laboratory evaluation. Her fasting glucose is 156 mg/dL and HbA1c is 8.2%. The biochemistry team explains that despite the body's continuous synthesis of glucose-6-phosphatase and the enzyme's standard free energy change (ΔG°') of +3.8 kJ/mol (unfavorable), gluconeogenesis proceeds efficiently in her liver during fasting states. Under fasting conditions, the actual free energy change (ΔG) becomes substantially more negative than ΔG°'. Which of the following best explains why gluconeogenesis remains thermodynamically favorable despite an unfavorable ΔG°'?
Answer choices
- DIncreased hepatic blood flow during fasting enhances enzyme kinetics and decreases the overall activation energy
- AHepatic enzymes in gluconeogenesis exhibit allosteric activation in response to elevated fasting glucose levels
- BThe intracellular ratio of products to reactants is maintained far below the equilibrium constant (Q << Keq), driving the reaction forwardCorrect answer
- CCoupling with ATP hydrolysis and the compartmentalization of gluconeogenic enzymes in mitochondria directly lowers the ΔG°' value
- EThe high NAD+/NADH ratio in fasting states directly reduces the free energy requirement for the gluconeogenic pathway
- FGlucagon-stimulated lipolysis produces fatty acids that directly couple to and favor gluconeogenic reactions
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