Gluconeogenesis is a metabolic process that makes glucose, a simple sugar that provides the body with energy from non-carbohydrate sources. These sources are typically amino acids, which are compounds that occur naturally in the tissues of plants and animals. Amino acids are known as the building blocks of proteins, and they play a vital role in metabolic functions. The energy produced from the breakdown of these substances is the only energy used in the brain, testes, erythrocytes and kidney medulla. Gluconeogenesis usually takes place in the liver, though at times, a very small amount may occur in the kidneys.
The process begins with pyruvic acid and ends with glucose. The reversal of this process is glycolysis, which starts with glucose and ends with pyruvic acid, but a few of the steps in the middle are different. Gluconeogenesis bypasses three of the steps in glycolysis because the energy required is too much to be reversed. Though many of the same amino acids are used, it is not an identical reversal.
The first step converts pyruvic acid to oxaloacetic acid. Then, if enough ATP is present in relation to the amount of Acetyl-CoA, the process continues with catalyzing enzymes at each stage propelling the process forward. The major steps of the pathway from start to finish are as follows:
Pyruvic Acid -> Oxaloacetic Acid -> Phosphoenolpyruvate Phosphoglycerate Bisphosphoglycerate Glyceraldehyde 3-Phosphate and Dihydroxyacetonephosphate Fructose-1, 6-Bisphosphate -> Fructose-6-Phosphate Glucose-6-Phosphate -> Glucose
This process is significant not just because it is the energy source for specific vital organs, but also because it helps stabilize blood glucose levels when things go wrong. During prolonged fasting, gluconeogenesis kicks in to produce the glucose needed to keep blood supplied with critical levels. Glucose is important for many body functions. Typically, when carbohydrates are consumed, blood glucose levels rise and the body stores this dietetic source of energy as glycogen in the liver.
When someone fasts, glycogen stores are processed and released into the blood as glucose. Over time, these glycogen stores in the liver are depleted, which triggers the body to process adipose triacylglycerols into fatty acids to be used as fuel, and glycerol to be used in gluconeogenesis. It also triggers amino acids to be released from the muscles. The presence of these and other precursors are the catalyst for this metabolic process to begin.