Difficulty: Medium
Correct Answer: None of the above (all are involved in gluconeogenesis)
Explanation:
Introduction / Context:
Gluconeogenesis is the anabolic pathway that synthesizes glucose from non-carbohydrate precursors such as lactate, glycerol, and glucogenic amino acids, primarily in the liver. This question tests recognition of processes that legitimately belong to gluconeogenesis.
Given Data / Assumptions:
Concept / Approach:
Evaluate each option for its role in gluconeogenesis. Oxaloacetate conversion through phosphoenolpyruvate and up the pathway is central; lactate to pyruvate (via LDH) supplies carbon; glucose-6-phosphatase dephosphorylation is required to release free glucose into blood.
Step-by-Step Solution:
1) Option A: Oxaloacetate is converted to phosphoenolpyruvate (via PEPCK) and eventually to glucose—clearly involved.2) Option B: Lactate enters as pyruvate, a major Cori cycle substrate—clearly involved.3) Option C: Glucose-6-phosphatase removes phosphate from G6P in the endoplasmic reticulum, producing exportable glucose—clearly involved.4) Therefore, none of the listed processes is excluded; select “None of the above.”
Verification / Alternative check:
Standard hepatic gluconeogenesis outlines include LDH (lactate to pyruvate), PEPCK/OAA routing, and glucose-6-phosphatase as essential steps for completing glucose output.
Why Other Options Are Wrong:
Each named process is a textbook step in gluconeogenesis; declaring any single one as “not involved” would contradict pathway biochemistry. Option E (“all not involved”) is the opposite of reality.
Common Pitfalls:
Misreading the stem and selecting “all of the above” when the logic demands “none of the above,” or confusing glycolytic enzymes with the bypass steps specific to gluconeogenesis.
Final Answer:
None of the above (all are involved in gluconeogenesis)
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