The distinguishing characteristics of eukary­otes are the nucleus and a variety of membrane-enclosed organelles with specific functions. - Albert L. Lehninger

Biochemistry asks how the remarkable properties of living organisms arise from the thousands of different biomolecules.

The remarkable similarity of metabolic pathways and gene sequences across the phyla argues strongly that all modern organisms are derived from a common evolutionary progenitor by a series of small changes (mutations), each of which conferred a selective advantage to some organism in some ecological niche.

Water is a polar solvent. It readily dissolves most bio­ molecules, which are generally charged or polar com­ pounds (Table 2-2); compounds that dissolve easily in water are hydrophilic (Greek, "water-loving"). In contrast, nonpolar solvents such as chloroform and benzene are poor solvents for polar biomolecules but easily dis­ solve those that are hydrophobic-nonpolar molecules such as lipids and waxes.