Carbohydrate Metabolism

C arbohydrates are the most abundant macro- molecules on our planet, in part because of the plant carbohydrates cellulose and starch, both composed of multiple conjugated glucose molecules.Cellulose is an important structural element of plant cell walls.Animals lack enzymes that can break down the cellulose into smaller glucose molecules, but they can break down starch into smaller glucose molecules.Animals also have glycogen, another carbohydrate composed of multiple conjugated glucose molecules.Many of us who exercise or play sports know that carbohydrates serve as a really good source of fuel during these strenuous endeavors.Unfortunately, most of us realize that overconsumption of carbohydrates can easily help us put on weight under nonexercise conditions.So, we know that carbohydrates can either be catabolized for energy (ATP) or used for anabolic functions, such as production of fatty acids.Carbohydrates are divided into three major groups based on their structures: (1) simple sugars (monosaccharides and disaccharides), such as glucose or sucrose (glucose and fructose); (2) complex carbohydrates, such as glycogen, starch, and cellulose, which are multiple conjugated glucose molecules; and (3) glycoconjugates, which are modified forms of glucose covalently attached to either proteins (glycoproteins) or lipids (glycolipids), which participate in important functions, such as immunity, and as components of cell membranes.This review covers all three groups and highlights their importance in maintaining physiological functions.