Textbook - BIOLOGICAL CHEMISTRY - Gubsky Yu.I. - 2000

Chapter III. METABOLISM OF MAJOR CLASSES OF BIOMOLECULES

CHAPTER 11. CARBOHYDRATE METABOLISM. I. AEROBIC AND ANAEROBIC GLUCOSE OXIDATION

Simple CARBOHYDRATES (Monosaccharides — glucose, fructose, galactose, mannose), upon Absorption in the intestinal tract and entry into Cells, undergo metabolic transformations that form The basis of their bioenergetic function. The most direct and substantial contribution to ATP generation is made by The oxidation of glucose to the End products of Catabolism — carbon dioxide and Water. In addition, a certain portion of carbohydrates continuously supplied to the body with food builds up energy stores of metabolic fuel in the form of Glycogen and neutral fats.

11.1. PATHWAYS OF INTRACELLULAR CATABOLISM OF MONOSACCHARIDES

The primary monosaccharide that yields the largest amount of ATP through catabolic oxidation reactions to simple end products is D-glucose, the main source of which in humans and animals is dietary plant starch. Other simple carbohydrates entering the body with food (fructose as a component of the disaccharide sucrose, galactose as a component of lactose, etc.) undergo metabolic transformations primarily after being converted into glucose phosphate esters.

Main Pathways of intracellular Glucose Catabolism:

- aerobic oxidation, resulting in The breakdown of glucose into carbon dioxide and water;

- glycolytic pathway (Glycolysis), resulting in The formation of intermediate catabolic products (pyruvic or lactic acid).

Glucose absorbed into the Blood in amounts exceeding the immediate energy demands of the body is stored as glycogen ("animal starch") or utilized for the synthesis of adipose tissue triacylglycerols.

Alternative pathways of glucose transformation leading to the PRODUCTION OF BIOLOGICALLY important metabolites:

- the Pentose Phosphate Pathway (shunt) of glucose oxidation, which yields sugar phosphates (pentoses, trioses, etc.) essential for other metabolic reactions and the reduced form of NADP⁺ (NADPH);

- conversion of glucose into glucuronic acid;

- conversion of glucose into ascorbic acid (a metabolic pathway operating only in certain animal species).