TAILIEUCHUNG - Biochemistry, 4th Edition P8

Biochemistry, 4th Edition P8. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | What Are the Properties of Water 33 among the H2O molecules. To be specific hydrophobic interactions between nonpolar molecules are maintained not so much by direct interactions between the inert solutes themselves as by the increase in entropy when the water cages coalesce and reorganize. Because interactions between nonpolar solute molecules and the water surrounding them are of uncertain stoichiometry and do not share the equality of atom-to-atom participation implicit in chemical bonding the term hydrophobic interaction is more correct than the misleading expression hydrophobic bond. Amphiphilic Molecules Compounds containing both strongly polar and strongly nonpolar groups are called amphiphilic molecules from the Greek amphi meaning both and philos meaning loving . Such compounds are also referred to as amphipathic molecules from the Greek pathos meaning passion . Salts of fatty acids are a typical example that has biological relevance. They have a long nonpolar hydrocarbon tail and a strongly polar carboxyl head group as in the sodium salt of palmitic acid Figure . Their behavior in aqueous solution reflects the combination of the contrasting polar and nonpolar nature of these substances. The ionic carboxylate function hydrates readily whereas the long hydrophobic tail is intrinsically insoluble. Nevertheless sodium palmitate and other amphiphilic molecules readily disperse in water because the hydrocarbon tails of these substances are joined together in hydrophobic interactions as their polar carboxylate functions are hydrated in typical hydrophilic fashion. Such clusters of amphipathic molecules are termed micelles Figure depicts their structure. Influence of Solutes on Water Properties The presence of dissolved substances disturbs the structure of liquid water thereby changing its properties. The dynamic H-bonding interactions of water must now accommodate the intruding substance. The net effect is that solutes regardless of whether they are

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