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Renin Angiotensin Mechanism.

Gluconeogenesis

 

Definition:

Gluconeogenesis is the production of glucose from non-sugar precursors.

  • Gluconeogenesis, mainly occurs in the liver, and involves the synthesis of glucose from compounds that are not carbohydrates.

  • When a cell is growing on a hexose such as glucose, and obtaining glucose for polysaccharide synthesis, there is no problem.

  • But when the cell is growing on other carbon compounds, glucose must be synthesized. This process is called gluconeogenesis.

  • Gluconeogenesis uses phosphoenolpyruvate, which is one of the intermediates of glycolysis, as starting material.

  • Gluconeogenesis is not a simple reversal of glycolysis alone.

  • The major precursors for gluconeogenesis are lactate, amino acids (which form pyruvate or TCA cycle intermediates), and glycerol (which forms DHAP).

  • The synthesis of 1 mole of glucose from 2 moles of lactate requires energy equivalent to about 6 moles of ATP.

Location:

  • Main is Liver, kidney, and intestine; not in skeletal muscle. 

Steps in Gluconeogenesis:

  • Pyruvate carboxylase converts pyruvate to oxaloacetate in the mitochondrion.

  • Oxaloacetate is converted to malate or aspartate, which travels to the cytosol and is reconverted to oxaloacetate.

  • Phosphoenolpyruvate carboxykinase converts oxaloacetate to phosphoenolpyruvate.

  • Phosphoenolpyruvate forms fructose 1,6-bisphosphate by reversal of the steps of glycolysis.

  • Fructose 1,6-bisphosphatase converts fructose 1,6-bisphosphate to fructose-6-phosphate, which is converted to glucose-6-phosphate.

  • Glucose-6-phosphatase converts glucose-6-phosphate to free glucose, which is released into the blood.

Significance:

  1. Gluconeogenesis meets the needs of the body for glucose when sufficient carbohydrate is not available from the diet or glycogen reserves.

  2. Glycogen stored in adipose tissue and in skeletal muscle is converted to glucose by glycogenolysis. However the stored glycogen may not be sufficient during heavy exercise, diabetic conditions,or during fasting etc. so during shortage, glucose is synthesized by gluconeogenesis process.

  3. A continual supply of glucose is necessary as a source of energy especially for the nervous system and erythrocytes.

  4. Gluconeogenesis mechanism is used to clear the products of the metabolism of other tissues from the blood, eg: Lactate, produced by muscle and erythrocytes and glycerol, which is continuously produced by adipose tissue.

Commonly Asked Questions.

  1. Write in short about Gluconeogenesis stating its significance in the body.
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