Chapter 5: Structures of the Major Compounds of the Body

Carbohydrates are systematically classified by carbon number, stereochemical configuration, and structural form, progressing from simple monosaccharides through ring structures and exploring the phenomenon of mutarotation and anomeric isomerism. The formation of glycosidic linkages in disaccharides and polysaccharides illustrates how structural diversity generates functional diversity, while derivatives including phosphorylated and amino sugars extend carbohydrate utility in cellular processes and signaling. Complex carbohydrate polymers such as glycosaminoglycans and proteoglycans are positioned as critical structural and functional components of connective tissue. Lipids are presented as a diverse class of hydrophobic molecules encompassing fatty acids with distinct saturation profiles, triacylglycerols serving energy storage, phosphoacylglycerols and sphingolipids forming membrane architecture, and cholesterol functioning in membrane fluidity and steroid hormone synthesis. The distinction between cis and trans fatty acid geometry is connected to dietary effects and metabolic consequence. Nitrogen-containing compounds—amino acids, purines, pyrimidines, and nucleotides—are introduced as structural units of proteins and nucleic acids, with emphasis on how ionizable groups confer charge-dependent properties. The chapter bridges molecular structure to clinical pathology through illustrative cases: diabetic ketoacidosis with nitroprusside detection methodology, acute gout reflecting urate crystal precipitation driven by tautomeric equilibria in uric acid, and bioaccumulation of environmental xenobiotics in adipose depots. Free radicals including superoxide and hydroxyl species are characterized as molecules with unpaired electrons capable of initiating oxidative damage implicated in aging and chronic disease states. Throughout, the chapter reinforces that molecular architecture directly determines physiologic function and disease mechanism.