Chapter 2: Molecules and Cells in Animal Physiology

Molecules and Cells in Animal Physiology explains how the elemental composition of animal bodies—particularly carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur—supports life through key biomolecules like proteins, nucleic acids, lipids, and carbohydrates. These molecules contribute to structural frameworks, energy storage, enzymatic reactions, and information transmission. The chapter explores how molecular properties affect physiological function, emphasizing noncovalent bonds, hydrophobic interactions, and the role of water as a solvent. Detailed sections examine the fluid mosaic model of cell membranes, with attention to lipid bilayers, membrane fluidity, cholesterol, and the role of membrane proteins in transport, signaling, and structural organization. The chapter highlights the importance of membrane-bound enzymes, gated ion channels, and receptor proteins as mediators of intracellular communication. Signal transduction pathways such as G-protein-coupled receptors and second messengers like cAMP are explored in depth. It also delves into the functional compartmentalization of cells, including the roles of organelles such as mitochondria, endoplasmic reticulum, and lysosomes. Lastly, the authors introduce genomics, proteomics, and metabolomics as powerful tools for understanding physiological processes on a systems biology level, helping bridge molecular knowledge to whole-animal function. This foundational knowledge sets the stage for all later discussions of cellular signaling, metabolic regulation, and physiological integration.