Summary

This chapter surveyed the chemical constituents of living cells, beginning with the distinction between the small, acid-soluble micromolecules -- amino acids, monosaccharides, nucleotides and lipids -- and the large, acid-insoluble macromolecules -- proteins, polysaccharides and nucleic acids -- that they polymerise to form. Amino acids, joined by peptide bonds, build up proteins whose biological activity depends on four hierarchical levels of structure: primary (amino-acid sequence), secondary (alpha-helices and beta-pleated sheets stabilised by hydrogen bonding), tertiary (the overall folded shape of one chain) and quaternary (the association of multiple polypeptide subunits, as in haemoglobin); proteins are further classified by shape (fibrous versus globular) and by the wide range of biological functions they perform. Carbohydrates were classified into monosaccharides, oligosaccharides and polysaccharides, with starch and glycogen serving storage roles and cellulose and chitin serving structural roles. Lipids, including fatty acids, triglycerides, phospholipids and steroids, were examined for their roles in energy storage and membrane structure. Nucleic acids -- DNA, a double helix built of deoxyribose-based nucleotides held together by complementary base pairing, and RNA, generally single-stranded and built of ribose-based nucleotides -- were shown to store and express genetic information. The chapter closed with enzymes: their six-class IUBMB classification by reaction type, t …