Gluconeogenesis and Cori cycle

Gluconeogenesis is a process of formation of glucose from intermediates. This process occurs mainly in liver and kidneys and it is considered as opposite directed reactions of anaerobic glycolysis, because reactions of anaerobic glycolysis are reversible. Only 3 reactions of anaerobic glycolysis are irreversible. These are reactions catalyzed by hexokinase, phosphofructokinase and pyruvatekinase. Another enzymes of gluconeogenesis catalyze these reactions. Hence, there are 3 round-way reactions of gluconeogenesis. These include formation of phosphoenolpyruvate; fructoso-6-phosphate from fructoso-1,6-diphosphate and glucose from glucose-6-phosphate.

1-st specific reaction of gluconeogenesis (1-st round way): formation of phosphoenolpyruvate.

2-nd reaction: fructoso-1,6-diphosphate is dephosphorylated and forms fructoso-6-phosphate.

Fructoso-6-phosphate is converted to glucoso-6-phosphate

3-rd reaction: glucoso-6-phosphate is dephosphorylated and glucose is formed

The importance of gluconeogenesis:

1. formation of glucose when deficiency of its is observed, e.g. in starvation

2. maintenance of homeostasis: pyruvate, lactate, glycogenic amino acids are converted to glucose. In some diseases of liver and kidneys gluconeogenesis is destroyed and lactate is increased in blood. It results in acidosis

Cori cycle and its role

Glycogenolysis, glycolysis and gluconeogenesis comprise intercommunicated system for maintenance of homeostasis and form Cori cycle:

Table 8. Cori cycle

The importance of Cori cycle consists in conservation of energy-riched lactate. Lactate isn’t lost, but it is converted to glucose.

Aerobic oxidation of glucose and its energetic value

The oxidation of glucose in aerobic conditions may order in 5 stages:

1. oxidation of glucose to pyruvate

2. oxidative decarboxylation of pyruvate to acetylCoA

3. usage of acetylCoA in citric acid cycle to NADH2, FPH2 and ATP

4. biologic oxidation, where energy and endogenic water are formed

5. oxidative phosphorylation in which ATP is formed

Thus, glucose is oxidized to pyruvate in anaerobic conditions. Pyruvate may be used in carboxylation and transamination.

Energetic value of aerobic glycolysis

4-2 = 2 ATP

Cytosolic NADH2 are oxidized through glycerophosphate’s and malate’s shunts.