Chapter 2: The Molecular Building Blocks

Chapter 2 introduces the families of compounds that are generally known as the primary metabolites: the carbohydrates, fats and oils, amino acids, and nucleotides. Learning about their molecules develops increasing understanding of the structures of organic compounds. Carbohydrate molecules serve as an introduction to functional groups and to asymmetric structures. The concept of polymers is introduced with the examples of cellulose, starch, and lignin. The composition of the molecules of fats and oils explains their water-repelling qualities, while the molecules’ degree of unsaturation determines whether a substance tends to be a solid or liquid at ambient temperature. Proteins, the most abundant macromolecules in living things, are composed of amino acid building blocks. Plants can synthesize all the essential amino acids that, in turn, need to be ingested by humans and animals through nutrition. Section 2.6 on nucleic acids provides an introduction to their monomers, the nucleotides. The chapter concludes with a simple scheme of general reaction pathways that plants use to assemble and reassemble plant molecules. Photos of representative plants accompany the chemical structures.