Biochimie, biotechnologies

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Néoglucogenèse Gluconeogenesis استحداث الجليكوز
Glycolyse Glycolysis هدم الجليكوز


Gluconeogenesis is the synthesis of glucose from noncarbohydrate precursors. The noncarbohydrate precursors of glucose are pyruvate, lactate, oxaloacetate, amino acids and glycerol. The noncarbohydrate precursors enter the gluconeogenic pathway in the forms of pyruvate, oxaloacetate and dihydroxyacetone phosphate. This metabolic pathway is important because glucose is the primary energy source for the brain. In addition, erythrocytes do not have mitochondria and derive all of their energy by glycolysis converting glucose into two molecules of lactate (fermentation)
Two major sites, the liver and the kidney, are involved in gluconeogenesis. The liver (90% of gluconeogenesis in the body), the kidney produces 10%. Little gluconeogenesis occurs in the other tissues. At a conclusion, the liver and kidneys maintain the glucose level in the blood so that the brain, muscle and red blood cells have sufficient glucose

Glycolysis, gluconeogenesis


What is the destination of pyruvate when resulted from glycolysis?
- Pyruvate can be transformed in lactate by LDH (fermentation)
- Pyruvate can be transported into the mitochondria where it is either converted into acetyl-CoA by pyruvate dehydrogenase and enters the citric acid cycle (Kerbs cycle) during a deficit in ATP. Excess in acetyl-CoA is a signal of the need for additional oxaloacetate.
- Pyruvate can be converted into oxaloacetate by pyruvate carboxylase and used for gluconeogenesis (when an excess in ATP.

يقع استحداث الجليكوز عند نفاد الجليكوجين المخزن في الكبد و الذي لا يكفي لأكثر من 10 ساعات. في هذه الحالة، تصنع خلايا الكبد الجليكوز من مصادر أخرى غير كربوهيدراتية. وقوع استحداث الجليكوز ينعكس على على أيض الدهنيات لأن الحمض الأكسالوأسيتي يذهب لصالح استحداث الجليكوز مما يوقف دورة كريبس و يحدث تكدس الأستيل كو أنزيم أ الذي يؤدي ألى ظهور الأجسام الكيتونية التي تعطي رائحة كريهة

See the figure bellow and find why the pyruvate must enter in the mitochondria to be carboxylated into oxaloacetate?

Oxaloacetate-malate in mitochondria

pyruvate must enter in the mitochondria to be carboxylated into oxaloacetate because the enzyme pyruvate carboxylase is found only in the matrix of the mitochondra.

How could oxaloacetate (previously formed from pyruvate) be transformed to PEP in case of gluconeogenesis?

This depends on organism types:
- In organisms where the enzyme involved in this transformation (PEP carboxykinase) is found only in the cytosol, oxaloacetate must be reduced to malate so that it can be transported across the mitochondrial membrane to the cytosol where the malate is reoxidized into oxaloacetate and goes on through gluconeogenesis. In human livers, PEP carboxykinase is found in both the mitrochondria and the cytosol.
-In organisms where the enzyme involved in this transformation (PEP carboxykinase) is found only in the mitochondria, oxaloacetate is converted into PEP (malate step not needed) in the mitochondria. PEP can be transported to the cytosol.

How could be regulated glycolysis and gluconeogenesis?

See figure bellow:

glycolysis and gluconeogenesis regulations

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Metabolism. Glycolysis, neoglucogenesis