Metabolic Pathways and Regulation · USMLE Step 1

In the liver during fasting state, which hormonal signal leads to decreased glycolysis and increased gluconeogenesis?

  1. Insulin
  2. Glucagon
  3. High glucose
  4. Thyroid hormone
Show answer and explanation

Correct answer: Glucagon

During fasting, glucagon levels rise, promoting cAMP-dependent phosphorylation events that inhibit glycolytic enzymes (like pyruvate kinase) and activate gluconeogenic enzymes, shifting metabolism toward glucose production.

Difficulty: Medium Question 5 of 19

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