Definition of gluconeogenesis Which statement correctly defines gluconeogenesis in metabolic biochemistry?

Introduction / Context:
Gluconeogenesis maintains blood glucose during fasting and intense exercise. It operates primarily in liver (and to a lesser extent kidney), synthesizing glucose when dietary intake is low and glycogen stores are depleted. Correctly defining this pathway differentiates it from glycogen metabolism and glycolysis.

Given Data / Assumptions:

• Main precursors: lactate (Cori cycle), glucogenic amino acids (e.g., alanine), and glycerol.
• Occurs predominantly in hepatocytes and renal cortex.
• Requires ATP/GTP and reducing equivalents; bypasses glycolytic irreversible steps.

Concept / Approach:

Gluconeogenesis literally means “new glucose formation.” It is distinct from glycogenesis (glycogen synthesis) and glycogenolysis (glycogen breakdown). It is also distinct from glycolysis (glucose breakdown). Selecting the definition that emphasizes synthesis from non-carbohydrate carbon sources yields the correct answer.

Step-by-Step Solution:

Verification / Alternative check:

Clinical physiology (e.g., overnight fasting) demonstrates hepatic glucose output dominated by glycogenolysis early, shifting to gluconeogenesis as fasting prolongs.

Why Other Options Are Wrong:

Options A, B, and C describe other pathways; Option E is a separate branch (pentose phosphate shunt) with different goals.

Common Pitfalls:

Confusing “gluco-” prefixes: glycogen synthesis and breakdown are not the same as new glucose synthesis from non-carbohydrate precursors.

Final Answer:

Synthesis of glucose from non-carbohydrate precursors