Provided the diet contains sufficient glucose precursors, most animals can synthesize enough glucose to meet their needs without a dietary source of carbohydrates.

Question

BlackTom AI · Accepted Answer

Gluconeogenesis in liver and kidney can supply glucose from noncarbohydrate precursors such as amino acids, lactate, glycerol and certain odd‑chain/propionate-derived intermediates.

1) Relevant knowledge points and concepts
- Gluconeogenesis is the metabolic pathway that synthesizes glucose from noncarbohydrate substrates (primarily in liver and renal cortex). Key substrates: alanine and other glucogenic amino acids (via pyruvate), lactate (via pyruvate), glycerol (from triglyceride breakdown → glycerol-3-phosphate → DHAP), and propionate/odd-chain fatty acids (→ succinyl-CoA → gluconeogenic intermediates). Long-chain even‑chain fatty acids yield acetyl‑CoA, which cannot be net converted to glucose in animals. Key irreversible enzymes: pyruvate carboxylase, PEP carboxykinase, fructose-1,6-bisphosphatase, glucose-6-phosphatase. Hormonal control: glucagon/cortisol/epinephrine stimulate; insulin inhibits.

2) Complete reasoning process step by step
- Dietary lack of carbohydrates forces metabolic reliance on gluconeogenesis.
- Proteins (amino acids) undergo transamination/deamination: alanine → pyruvate; other glucogenic amino acids → TCA intermediates → OAA.
- Lactate from anaerobic glycolysis is converted to pyruvate (lactate dehydrogenase).
- Glycerol from triglycerides is phosphorylated to glycerol-3-phosphate → DHAP (glycolytic intermediate).
- Pyruvate → (pyruvate carboxylase) → oxaloacetate → (PEP carboxykinase) → PEP → … → fructose-1,6-bisphosphate → (fructose-1,6-bisphosphatase) → fructose-6-phosphate → glucose-6-phosphate → (glucose-6-phosphatase) → glucose, which is released into blood.

3) Intermediate steps (pathway highlights)
- Pyruvate + CO2 + ATP → oxaloacetate (pyruvate carboxylase)
- Oxaloacetate → PEP + GTP (PEP carboxykinase)
- Fructose-1,6-BP → Fructose-6-P (fructose-1,6-bisphosphatase)
- Glucose-6-P → Glucose (glucose-6-phosphatase)

4) Why the correct answer is correct
- Given adequate noncarbohydrate precursors and intact gluconeogenic machinery, most animals (including humans and ruminants) can maintain blood glucose via gluconeogenesis without dietary carbohydrates. Ruminants, for example, depend heavily on propionate and gluconeogenesis. Thus the statement is true.

5) Why the alternative (False) is incorrect
- Saying it is false ignores the well-established capacity of animals to produce glucose endogenously from precursors. The only caveat—fatty acids (even-chain) cannot be converted to glucose except for glycerol or odd-chain products—is already encompassed by “provided the diet contains sufficient glucose precursors.”

6) Conclusion
- The statement is True, which matches the provided answer.

Provided the diet contains sufficient glucose precursors, most animals can synthesize enough glucose to meet their needs without a dietary source of carbohydrates.True/False

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