Chapter 15: Physiologic Carbohydrates & Functions

At the center of mammalian metabolism is glucose, the universal energy source for the fetus and the primary precursor for all other bodily sugars, including those found in nucleic acids and milk. The emerging field of glycomics focuses on the glycome—the complete set of sugars within an organism—deciphering the complex biological information stored in oligosaccharide sequences and linkages. Sugars are categorized by their molecular complexity into monosaccharides, disaccharides, oligosaccharides, and polysaccharides, each serving distinct physiological roles. A key focus is the structural diversity of monosaccharides, driven by various forms of isomerism such as d- and l-designations, pyranose and furanose ring formations, and the existence of epimers like galactose and mannose. Clinical conditions such as diabetes mellitus, galactosemia, and lactose intolerance highlight the medical importance of proper carbohydrate processing and the biochemical impact of enzyme deficiencies. The chapter also explores large-scale polymers, distinguishing between storage molecules like starch in plants and glycogen in animals, and structural molecules like cellulose, which humans cannot digest but which remains a vital component of dietary fiber. Finally, the discussion extends to complex carbohydrates, including glycosaminoglycans that provide tissue lubrication and glycoproteins found on cell surfaces that facilitate essential biological signaling and recognition within the glycocalyx.