Glycolysis and Gluconeogenesis

Pathways like Glycolysis and Gluconeogenesis interact in the cell in such a way, if one is comparatively active the other pathway would be inactive at the same time. If both pathways would be active at the same time, it results in the hydrolysis of four energy intermediates like ATP and GTP per each pathway. Both pathways are thermodynamically exergonic under same cellular conditions. This provides none of the thermodynamic barrier to these cellular processes. Therefore, the amount and the relative activities of specific enzymes for each pathway can be controlled by the cell. In this way, both cellular processes can never be active at the same time. We can determine the rate of “Glycolysis” by determining the concentration of glucose. And the rate for “Gluconeogenesis” can be determined by measuring the concentration of lactate.

Both pathways can be explained one by one:

1. Glycolysis

2. Gluconeogenesis

1-Glycolysis:

Glycolysis is the first metabolic pathway that we confronted. It is also called an ancient cellular pathway host by a number of organisms. We define glycolysis as;

“Glycolysis is the sequence of reactions that metabolizes one molecule of glucose to two molecules of pyruvate with the concomitant net production of two molecules of ATP”

It is an anaerobic process, which does not require much oxygen, as it was evolved before the aggregation of considerable amount of oxygen in the living environment. The end product pyruvate can further be oxidized aerobically or anaerobically. Under aerobic conditions, CO2 is produced from complete oxidation of pyruvate, which generates much ATP.

Major steps of pathway:

It is a multi-step cellular process and occurs in the cytoplasm of living cells. There are total six enzymes that operate this cellular metabolic process. Energy generates in the first and the third step of the metabolic pathway. Thus, there are two ATP molecules that can be extended in the pathway. Furthermore, along this process, Glucose (Six carbon molecule) can be split into two molecules of three-carbon compound, called pyruvate.

• Glycolysis simply called a breakdown of glucose molecule takes place in the human body cells. This reaction occurs in the cytosol of the cell. Glycolysis takes place in the presence or in the absence. Lactate is the end product in the absence of oxygen while glucose is completely oxidized to CO2 and H2O in the presence of oxygen.

• It is the major pathway to provide ATP to those tissues that lack mitochondria. For example; erythrocytes, cornea, etc.

• Glycolysis is very important for proper brain functioning. Brain does not use fat directly to drive energy so it completely dependent on glucose oxidation.

• Glycolysis can be considered a central pathway that connects many other pathways. So its intermediates are indirectly used in the formation of many other products.

• Reverse of glycolysis with minor changes leads to the formation of Glucose again.

• net reaction of anaerobic glycolysis:

Glucose + 2ADP + 2Pi → 2Lactate + 2ATP

2-Gluconeogenesis:

Gluconeogenesis is the formation of glucose from non-carbohydrate compounds. Pyruvate, Glucogenic amino acids, propionate, and glycerol are the major precursors. This catabolic reaction occurs in the cytosol of liver cells and to some extent in kidney cells. This reaction has crucial importance in the human body such as;

Major steps in Gluconeogenesis:

• Some metabolites start accumulating in the body. Gluconeogenesis clears them all from the blood by the formation of glucose.

• Some body cells like the brain and erythrocytes completely rely on glucose for energy consumption. So, gluconeogenesis helps the body in the formation of glucose.

• During anaerobic respiration glucose is the main source to provide energy in the form of ATP.

During fasting for a long time, gluconeogenesis helps to meet the requirements of the body for glucose and also helps to produce intermediates of the TCA cycle that produce CO2 and H2O. In this way, it plays a vital role in the human body and other living species.

• Net reaction of Gluconeogenesis:

2 Pyruvate + 4ATP + 2GTP + 2NADH + 2H+ + 6H2O → Glucose + 2NAD+ + 4ADP + 2GDP + 6Pi + 6H+