Gluconeogenesis
Gluconeogenesis is the metabolic pathway that makes glucose from non-carbohydrate precursors such as lactate, glycerol, pyruvate, and some amino acids.
What gluconeogenesis is
Gluconeogenesis is the production of glucose from molecules that are not already carbohydrates. The pathway helps maintain glucose availability during fasting, prolonged exercise, low-carbohydrate intake, and other situations where cells still need a glucose supply.
Not just glycolysis in reverse
Much of the pathway follows glycolysis in the opposite direction, but three glycolysis steps are strongly irreversible under cell conditions. Gluconeogenesis uses bypass enzymes to move around those steps, including pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase.
Where the carbon comes from
Lactate from anaerobic metabolism can be converted back toward pyruvate. Glycerol from fat breakdown can enter as a three-carbon intermediate. Several amino acids can supply carbon skeletons after their amino groups are removed. These inputs let the body make glucose without starting from stored glycogen.
Organs and compartments
In mammals, the liver is the main organ for releasing newly made glucose into the blood. The kidney cortex can contribute more during longer fasting or acid-base stress. The reactions are split across mitochondria, cytosol, and the endoplasmic reticulum, so transport between compartments is part of the pathway.
Energy cost
Building glucose costs energy. For each glucose molecule made from pyruvate, the pathway consumes ATP, GTP, and reducing power. That cost is one reason gluconeogenesis is regulated carefully rather than running at full speed all the time.
Hormonal control
Insulin generally reduces gluconeogenesis after meals, while glucagon and stress hormones tend to increase it when blood glucose is low or energy demand is high. Cells also regulate key enzymes through substrate availability, energy state, and gene expression.
Links to other pathways
Gluconeogenesis connects with glycolysis, amino acid metabolism, fat metabolism, the citric acid cycle, and the Cori cycle. In plants and many microbes, carbon-conserving routes such as the glyoxylate cycle can help supply intermediates that support sugar synthesis.
Why it matters
The pathway helps keep blood glucose available for tissues that depend heavily on it, such as red blood cells and parts of the brain. It is also important in diabetes, fasting physiology, exercise recovery, inherited enzyme deficiencies, and metabolic engineering.