Carbohydrate Metabolism-Glycolysis

Glucose is the chief form of sugar moiety present in blood and other body fluids. The digestion of food carbohydrates, such as starch, sucrose, and lactose produces the monosacchandes like glucose, fructose and galactose, which pass into the blood stream. The study of synthesis or Anabolism and degradation or Catabolism of biomolecules is biochemically known  as metabolism.

Anabolism (Synthesis) + Catabolism (Degradation) = Metabolism

Since glucose is the most chief carbohydrate existing in physiological amounts in the body and is easily absorbed from the diet, the metabolism of carbohydrate resolves itself to the study of the metabolism of glucose and its main derivatives. The monosaccharides like galactose and fructose are converted to glucose in the liver. All the monosaccharides are totally absorbed in the small intestine.The glucose in the circulating blood and tissue fluids is drawn upon by all the cells of the body and used for the manufacture of energy. Usually carbohydrate metabolism supplies more than half of the energy requirements of the body. In fact the brain largely depends upon

carbohydrate metabolism as a source of energy and quickly ceases to function properly when the blood glucose level falls much below normal.

Carbohydrate is the source of energy:The major function of carbohydrate in metabolism is to serve as fuel and get oxidised to offer energy for other metabolic processes.The metabolic intermediates are used for different biosynthetic reactions.

For this reason, carbohydrate is utilized by the cells mainly in the form ofglucose. A major part of dietary glucose is converted to glycogen for storage in liver. Glucose is degraded in the cell by way of a sequence of phosphorylated intermediates mainly via two metabolic pathways.

Glycolysis

 

Glycolysis

Oxidation of glucose to pyruvate is called glycolysis. It was first described by Embden-Meyerhof and Parnas. Therefore it is also called as Embden-Meyerhof pathway. Glycolysis occurs virtually in all cells of tissues. Erythrocytes and nervoustissues derive the energy chiefly from glycolysis. This pathway is unique in the sense that it can proceed in both aerobic  or in presence of O2 and anaerobic in the absence of O2 conditions. All the enzymes of glycolysis are found in the extra mitochondrial soluble fraction of the cell, the cytosol or cytoplasm .

Reactions of glycolytic pathway

Sequence of reactions of glycolytic pathway which degrades glucose to pyruvate are represented below. The sequence of reactions taking place in glycolysis is explained below