In subsequent chapters of this book, we discuss cellular processes in much greater detail. We begin (in Chapter 2) with a discussion of the chemical nature of the building blocks of cells and the basic chemical processes required to understand the macromolecular processes discussed in subsequent chapters. We go on to discuss the structure and function of proteins (in Chapter 3). Chapter 4 discusses many of the techniques biologists use to culture and fractionate cells and to visualize specific proteins and structures within cells. Chapter 5 describes how DNA is replicated, how segments of DNA are copied into RNA, and how proteins are synthesized on ribosomes. Chapter 6 describes many of the techniques used to study genes, gene expression, and protein function, including the generation of animals with specific genetic mutations. Biomembrane structure is the topic of Chapter 7. Gene and chromosome structure and the regulation of gene expression are covered in Chapters 8, 9, and 10. The transport of ions and small molecules across membranes is covered in Chapter 11, and Chapter 12 discusses cellular energetics and the functions of mitochondria and chloroplasts. Membrane biogenesis, protein secretion, and protein trafficking—the directing of proteins to their correct subcellular destinations—are the topics of Chapters 13 and 14. Chapters 15 and 16 discuss the many types of signals and signal receptors used by cells to communicate and regulate their activities. The cytoskeleton and cell movements are discussed in Chapters 17 and 18. Chapter 19 discusses the cell cycle and how cell division is regulated. The interactions among cells, and between cells and the extracellular matrix, that enable formation of tissues and organs are detailed in Chapter 20. Later chapters of the book discuss important types of specialized cells—stem cells (Chapter 21), neurons (Chapter 22), and cells of the immune system (Chapter 23). Chapter 24 discusses cancer and the multiple ways in which cell growth and differentiation can be altered by mutations.