1 - Biophysical Chemistry of Physiological Solutions

Abstract

This chapter introduces some of the fundamental concepts of cell physiology. The chapter describes certain physicochemical properties of water, electrolytes, and proteins that are relevant for understanding the structure and function of living cells. The chapter discusses the structure and properties of water, the interactions between water and ions, protons in solution, interactions between ions, cell cations, cell anions, trace elements, basic definitions of solute transport, measurement of electrolytes and membrane potential, and ionophores. Electrostatic interactions between ions and water based on Coulomb's law account for the enthalpy of hydration, as well as for the sequence of ionic mobilities of the hydrated alkali cations. Intracellular water exhibits thermodynamic properties similar to extracellular water. Salts and nonelectrolytes dissolve in cell water with nearly the same solubility and activity as in extracellular water; even the viscosities are similar. Protons in solution are hydrogen-bonded to water to form H3O+, which is further hydrated because of electrostatic forces. Protons migrate through water by a Grotthus chain mechanism; in contrast, other hydrated ions migrate through water as hard spheres that interact with water dipoles according to the ionic radius and charge. The predominant biological cations are potassium and sodium, calcium, and magnesium. Metalloproteins are tightly associated with certain proteins and enzymes. Active transport and passive transport are discussed under solute transport. Membrane-bounded compartments inside cells may contain different concentrations of solutes than does the bulk cytoplasm. Ionophores with a high degree of ion selectivity are useful tools in cell physiology experiments. The study of ion transport mediated by ionophores has provided instructive models for understanding the mechanisms of membrane transport..