Introduction to Gluconeogenesis

The biochemical process of preparing glucose from the non-glucose sources within the cells is called gluconeogenesis. This process does not include stored glycogen to transform it into glucose rather uses different molecules to produce this substrate. It generally takes place in the liver and partly in the small intestine and kidneys following a specific gluconeogenesis pathway. Here, we will elaborately study the definition, process, and pathway of gluconeogenesis.

Definition of Gluconeogenesis

The biochemical reaction where the non-glucose molecules or non-sugar precursors are transformed into active glucose within the tissues of different organs in a human body is called gluconeogenesis. This process involves various chemical steps occurring in the liver, kidneys, and partly in the small intestine where the non-sugar precursors or molecules are transformed into glucose.

According to the gluconeogenesis definition, this process does not produce glucose from stored glycogen. In fact, we can also conclude that it is the exact opposite of glycolysis, the biochemical process where glucose is broken down into different non-sugar products.

Features of Gluconeogenesis

  • This is a way to produce glucose from non-glucose precursors.

  • This is a biochemical reaction where molecules that are not carbohydrates produce glucose in the process.

  • This process includes phospho-enol-pyruvate, an intermediate product of the glycolysis pathway. It is the starting material for the gluconeogenesis cycle.

  • There are various enzymes involved in the formation of glucose from this compound at different steps.

  • The outcome of the gluconeogenesis in liver is simply the opposite of glycolysis but the path is entirely different due to the involvement of various enzymes and the formation of byproducts.

Gluconeogenesis Pathway

To understand how glucose is formed from the pyruvate molecules, let us find out the different gluconeogenesis steps in this process.

  • This biochemical process begins in the cells of the kidneys and liver. To be precise, the site of gluconeogenesis is either cell cytoplasm or mitochondria of the cells in these two organs.

  • The two pyruvate molecules are first carboxylated to create oxaloacetate. This process needs one ATP molecule for energy.

  • Oxaloacetate is then reduced to form malate in the presence of NADH. This is done to transport oxaloacetate outside the mitochondrial plasma.

  • It is then transformed into phospho-enol-pyruvate due to the influence of the PEPCK enzyme.

  • Phospho-enol-pyruvate is then converted into fructose-1,6-biphosphate and eventually to fructose-6-phosphate. This process also uses ATP molecules for energy. This step in the gluconeogenesis cycle can be considered as the reverse of glycolysis.

  • The next step transforms fructose-6-phosphate to glucose-6-phosphate in the presence of an enzyme named phospho-gluco-isomerase.

  • Glucose-6-phosphate then gets transformed into glucose in the endoplasmic reticulum of the cell. It occurs due to the presence of the glucose-6-phosphatase enzyme. In this process, glucose-6-phosphatase loses a phosphate molecule and gives it to an ADP to form an ATP molecule.

The gluconeogenesis pathway diagram, will help you understand how the process takes place in the presence of the various enzymes and ATP (energy). To understand the entire process, keep the reaction substrate in mind and follow the stepwise transformation of the molecule to form glucose in the end.

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Follow the steps to find out the specific gluconeogenesis enzymes required for the transformation of the molecules into glucose. Every enzyme has a specific function in this biochemical reaction cycle. To understand the functions of the enzymes, follow each step given in the diagram of this reaction one by one. The formation of glucose also takes place from the transformation of gluconeogenic amino acids through amino acid catabolism.

Significance of Gluconeogenesis

  • The prime importance of gluconeogenesis is to provide glucose, the respiratory substrate, for the production of energy when sufficient carbohydrates are not available for energy production. It happens when our body is witnessing a lack of stored glucose in the form of glycogen in the liver and muscles.

  • When someone is exercising heavily or in dire need of energy, the formation of glucose occurs with this process. According to gluconeogenesis meaning, glucose is formed from non-sugar substrates in the liver and kidney and partly in the small intestine. This process is ideal to get glucose in the system when a person is suffering from diabetic conditions, doing heavy exercise, or fasting.

  • This process ensures a continuous supply of the prime respiratory substrate (glucose) for erythrocytes and the nervous system.

  • Another significance of the gluconeogenesis reactions is to clear out the tissues from the metabolic byproducts present in the blood. These byproducts flow from the tissues to the blood and need to be eradicated. For instance, it removes lactate from erythrocytes and muscles. It also removes glycerol produced in the adipose tissue cells.

There is no difference between glucogenesis and gluconeogenesis as they refer to the same reaction in which glucose is produced from the non-carbohydrate molecules present in the kidneys and liver. Hence, glucogenesis Vs gluconeogenesis yields the same reaction. The gluconeogenesis definition is similar to that of glucogenesis.

FAQs (Frequently Asked Questions)

1. What is the function of ATP in gluconeogenesis?

Ans: ATP molecules work as the energy source for the different steps of this biochemical reaction. It supports the formation of glucose from the non-sugar substrates in certain steps.

2. When do the tissue cells perform gluconeogenesis?

Ans: When there is a dire need for glucose for various cellular functions in certain conditions and there is a lack of glucose originating from glycogen, this biochemical reaction occurs to bridge the gap. It generally happens in the tissues of the kidneys and liver. It also happens in the small intestine to some extent.