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Gluconeogenesis: Pathway, Enzymes and Regulation

Last reviewed 27 Oct 2026 · 4 min read

Contents
  1. What gluconeogenesis does
  2. Starting materials
  3. Relation to glycolysis
  4. Energy cost
  5. Hormonal and allosteric control
  6. Where it matters
  7. Frequently asked questions
  8. Is gluconeogenesis the reverse of glycolysis?
  9. Where does it take place?
  10. Can fatty acids be converted into glucose?
  11. What is the difference between gluconeogenesis and glycogenolysis?
  12. References

In short: Gluconeogenesis is the synthesis of new glucose from non-carbohydrate precursors such as lactate, glycerol and glucogenic amino acids. It happens mainly in the liver, and to a lesser extent in the kidney cortex, and keeps blood glucose steady during fasting. It uses most of the glycolysis enzymes in reverse, but three irreversible glycolytic steps are bypassed by different enzymes.

What gluconeogenesis does

Tissues such as the brain and red blood cells depend heavily on glucose. When dietary glucose is not available, the body first releases glucose from liver glycogen (glycogenolysis, a separate process). As glycogen runs low, gluconeogenesis supplies glucose from other molecules, which helps prevent hypoglycaemia (abnormally low blood glucose).

Starting materials

PrecursorWhere it comes from
LactateProduced by red blood cells and working muscle; returned to the liver (Cori cycle)
GlycerolReleased from triglycerides in adipose tissue
Glucogenic amino acidsMainly alanine and glutamine, from muscle protein breakdown during fasting; most amino acids can be converted to glucose, but leucine and lysine cannot
Propionyl-CoAFrom odd-chain fatty acids; ordinary even-chain fatty acids cannot give a net gain of glucose in animals

Relation to glycolysis

Gluconeogenesis is not simply glycolysis run backwards. Seven of the ten glycolytic reactions are reversible and are used in both directions. The other three, catalysed by pyruvate kinase, phosphofructokinase-1 and hexokinase/glucokinase, are strongly energy-releasing and effectively irreversible. Gluconeogenesis bypasses them with different enzymes. For the glycolysis steps themselves, see glycolysis: pathway and net yield.

Glycolysis step (irreversible)Gluconeogenesis bypassNotes
Phosphoenolpyruvate (PEP) → pyruvate (pyruvate kinase)Pyruvate → oxaloacetate (pyruvate carboxylase), then oxaloacetate → PEP (PEP carboxykinase)Carboxylase needs ATP, bicarbonate and biotin and works in the mitochondria; PEP carboxykinase uses GTP
Fructose-6-phosphate → fructose-1,6-bisphosphate (phosphofructokinase-1)Fructose-1,6-bisphosphate → fructose-6-phosphate (fructose-1,6-bisphosphatase)Key control point of the pathway
Glucose → glucose-6-phosphate (hexokinase/glucokinase)Glucose-6-phosphate → glucose (glucose-6-phosphatase)Occurs in the endoplasmic reticulum of liver and kidney cells, which is why muscle cannot release free glucose

Because oxaloacetate is also an intermediate of the TCA cycle, gluconeogenesis and the cycle share this molecule, and acetyl-CoA from fatty acid oxidation activates pyruvate carboxylase.

Energy cost

Making one glucose from two pyruvate molecules uses 4 ATP, 2 GTP and 2 NADH, which is about six high-energy phosphate bonds. Glycolysis, in the other direction, yields a net 2 ATP, so the process cannot run in both directions at the same time without a net loss of energy. The ATP for gluconeogenesis comes mainly from the oxidation of fatty acids in the liver, through the TCA cycle and the electron transport chain.

Hormonal and allosteric control

Opposite reactions are controlled together so that glycolysis and gluconeogenesis are not both active.

  • Glucagon (released when blood glucose is low) raises cAMP in the liver, which lowers fructose-2,6-bisphosphate. This relieves the inhibition of fructose-1,6-bisphosphatase and favours gluconeogenesis.
  • Insulin (released after meals) has the opposite effect: it promotes glycolysis and glycogen storage and reduces the expression of key gluconeogenic enzymes.
  • Cortisol supports gluconeogenesis during prolonged fasting and stress, partly by increasing enzyme synthesis.
  • Fructose-2,6-bisphosphate activates phosphofructokinase-1 and inhibits fructose-1,6-bisphosphatase.
  • Acetyl-CoA activates pyruvate carboxylase, while AMP inhibits fructose-1,6-bisphosphatase.

Where it matters

Gluconeogenesis is important in prolonged fasting and starvation, in intense exercise through the Cori cycle, and in diabetes, where excessive hepatic glucose production contributes to high blood glucose. It is also relevant to some drug effects: for example, alcohol metabolism raises the NADH-to-NAD⁺ ratio in the liver and can impair gluconeogenesis, which is one reason heavy drinking without food can cause hypoglycaemia.

Frequently asked questions

Is gluconeogenesis the reverse of glycolysis?

Not exactly. Seven reactions are shared, but three irreversible steps are bypassed by different enzymes.

Where does it take place?

Mainly in the liver, with a smaller contribution from the kidney cortex, which increases in prolonged fasting. The pathway spans the mitochondria, the cytosol and the endoplasmic reticulum.

Can fatty acids be converted into glucose?

Not to a net extent in humans. The glycerol part of triglycerides can, but the acetyl-CoA from even-chain fatty acids cannot be turned into new glucose carbon.

What is the difference between gluconeogenesis and glycogenolysis?

Glycogenolysis breaks down stored glycogen to release glucose; gluconeogenesis makes new glucose from other molecules.

References

  1. Berg JM, Tymoczko JL, Gatto GJ, Stryer L. Biochemistry, chapter on gluconeogenesis and glycolysis, W. H. Freeman (current edition).
  2. Nelson DL, Cox MM. Lehninger Principles of Biochemistry, chapter on carbohydrate biosynthesis (gluconeogenesis), W. H. Freeman (current edition).

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