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Biochemistry and Molecular Biology Education 29 (2001) 54}59

Water: its importance to life
Martin F. Chaplin*
School of Applied Science, South Bank University, 103 Borough Road, London SE1 0AA, UK

Abstract Textbooksincreasingly include material concerning the importance of water but this topic is often treated over-simplistically with insu$cient attention being given to the central position of water in life processes. In this article, modern views of the fundamental role that water plays in biochemical function and process are summarized. The importance of water in the structures of nucleic acids and proteins isexplained. 2001 IUBMB. Published by Elsevier Science Ltd. All rights reserved.
Keywords: Water; Structure; Hydrogen bonding; Proteins; Nucleic acids

1. Introduction Although often perceived to be pretty ordinary, water is the most remarkable substance. We wash in it, "sh in it, swim in it, drink it and cook with it, although probably not all at the same time. We are about two-thirds water andrequire water to live. Life as we know it could not have evolved without water and dies without it. Droughts cause famines and #oods cause death and disease. Because of its clear importance, water is the most studied material on Earth. It comes as a surprise, therefore, to "nd that it is so poorly understood, not only by people in general, but also by scientists working with it everyday. Textbooksare including increasing amounts of material concerning water. However, this material is usually concentrated in one chapter and its importance is rarely emphasized elsewhere. Chapters on proteins and nucleic acids, for example, often discuss structural and functional details of these macromolecules with little prominence given to the pervasive e!ects of the surrounding water. Other areas, such asmetabolism, often ignore the many functions of water altogether. This lack of emphasis, evidenced in part from the textbooks' indexes, results from the multidisciplinary nature of the water literature and the di$culty in bringing together the wide but often thinly-spread information available. Water seems, at "rst sight, to be a very simple molecule, consisting of two hydrogen atoms attached to an* Tel.: #44-207-815-7970; fax: #44-207-815-7999. E-mail address: chaplimf@sbu.ac.uk (M.F. Chaplin).

oxygen atom and indeed, few molecules are smaller. Its size, however, belies the complexity of its properties, and these properties seem to "t ideally into the requirements for carbon-based life as can no other molecule. Organisms consist mostly of liquid water, which performs many functionsand should never be considered simply as an inert diluent. Nevertheless, in spite of much work many of the properties of water are puzzling. It has often been stated that life depends on the anomalous properties of water. In particular, the large heat capacity and high water content in organisms contribute to thermal regulation and prevent local temperature #uctuations. The high latent heat ofevaporation gives resistance to dehydration and considerable evaporative cooling. Water is an excellent solvent due to its polarity, high dielectric constant and small size, particularly for polar and ionic compounds and salts. Indeed its solvation properties are so impressive that it is di$cult to obtain really pure water. Water ionises and allows easy proton exchange between molecules, socontributing to the richness of the ionic interactions in biology. The structuring of water around molecules allows them to sense and be sensed at a distance. The unique hydration properties of water towards biological macromolecules (particularly proteins and nucleic acids) to a large extent determine their three-dimensional structures, and hence their functions, in solution. 2. Structure Water has the...