Agua (elemento clásico)

The néoglucogenèse (or néoglycogénèse) is the synthesis of the Glucose starting from not-glucidic precursors. It is strictly speaking the reverse of the Glycolyse; however, the borrowed biochemical ways, although comprising common points, are not identical.

Utility

It is a mechanism which occurs at the time of a prolonged fast. One observes a synthesis of Glucose in the liver starting from the Glycérol resulting from the hydrolysis of the lipidic reserves of the fat fabrics, or starting from the Amino-acid resulting from the hydrolysis of the Protéine S (muscular, primarily).

At the man, as soon as the glycogen reserves are exhausted (what occurs after one day of fast), the sources of glucose by néoglucogenèse are mainly the amino-acids (45%) and, with a less degree, the lactate (30%) and the glycerol (25%).

This operation can be realized by the Foie (of the Glucose starting from the hepatic Glycogène) or by the muscles. It makes it possible to provide to the bodies which cannot use lipids or proteins, like the brain, of glucose in any time, even when the reserves in Glycogène became exhausted.

Ways of biosynthesis

There are several precursors for the synthesis of glucose (some amino-acid, Lactate, Glycérol, Pyruvate). Intermediaries of the Cycle of Krebs can also be transformed into intermédiares of the way of néoglucogenèse.

Starting from lactate

The Lactate can be detoxified by giving pyruvate and will be retransformé in glucose.

Lactate + NAD+ - > Pyruvate + NADH + H+

Starting from the pyruvate

The conversion of the Pyruvate into Glucose is the center lane and uses the same metabolic ways partly as the Glycolyse (but in the other direction).

It is controlled by hyperglysemic Hormone S (Glucagon) which act, inter alia, on the Hépatocyte S.

Three of the stages of glycolysis are not reversible, one borrows diversions then. It is a question of shunting these three stages (requiring either a ATP or a NADP).

Pyruvate - > Phosphoénol pyruvate (PEP) - >…

  • the pyruvate is initially made transform in the Mitochondrie hepatic cells into Oxaloacétate (which is also the last intermediary of the Cycle of Krebs) by the enzyme pyruvate carboxylase , enzyme which needs Biotine (and thus of Acetyl-coA). This first chemical conversion consumes a molecule of CO2 and consumes a Adénosine triphosphate.

  • Then the oxaloacétate will be transported by the shuttles malate/aspartate: the oxaloacétate is transformed into Malate (by consuming a NAD) or Aspartate, transported by the shuttles, then retransformé in oxaloacétate in the Cytosol, regenerating a NAD.
  • Lastly, the oxaloacétate is transformed into Phosphoénol pyruvate (PEP) by PEP carboxykinase or PEPCK by consuming a GTP and by releasing a molecule of CO2.

For the other stages, one goes up the diagram of the Glycolyse.

… - > Fructose-1,6-bisphosphate - > Fructose-6-phosphate - >…

This passage will be done under the action of the enzyme fructose bisphosphatase which will remove a grouping phosphates by Hydrolyze. This enzyme is controlled in a allosteric way: - by the ATP which activates it - by the F 2,6 di-P and the AMP which inhibit it.

… - > Glucose-6-phosphate - > Glucose

Lastly, the glucose-6-phosphatase will remove the last grouping phosphates with glucose-6-phosphate (G6P) what gives Glucose. This enzyme is strictly localized in the Endoplasmic Reticulum of the cell, and the G6P must thus be caused to beforehand this cellular compartment by the G6P translocase.

Assessment G°' = -6 Kcal/mol

Starting from glycerol

It occurs primarily in the liver starting from the Glycérol coming for example from the complete hydrolysis of the Triglycérides. It uses the following way:

  • Glycerol + ATP ---> Glycerol-phosphate + ADP (glycerol-phosphate kinase)

  • Glycerol-phosphate + NAD+ ---> Dihydroxyacetone-phosphate + NADH, H+ (glycerol-phosphate déshydrogénase)
  • Dihydroxyacetone-phosphate ---> Glycéraldéhyde-3-phosphate

From there, the way joined that of the néoglucogénèse starting from the pyruvate, i.e.:

  • Glycéraldéhyde-3-phosphate + Dihydroxyacetone-phosphate ---> Fructose-1,6-bisphosphate

  • Fructose-1,6-bisphosphate + H2O ---> Fructose-6-phosphate + Pi

  • Fructose-6-phosphate ---> Glucose-6-phosphate

  • Glucose-6-phosphate + H2O ---> Glucose + Pi

Assessment Are needed two glycerol (compound with 3 Carbons) to synthesize a glucose.

Starting from the amino-acids

The consumption of the Amino-acid takes place in the event of ultimate need. The amino-acids come from proteins of the muscles. They can beings transformed into intermediaries of glycolysis, and can thus lead to the formation of glucose.

Medicine

Only certain bodies can make the néoglucogenèse: the Liver, the Kidney S as well as the Internal .

See too

Internal bond

External bond

The chemical logic behind gluconeogenesis

References

Random links:District of Lyon | Mondorff | Philippe Suchard | Oxfam in Belgium | ISO 639: NOR