The Biological Structure of Water
Water is a substance with the chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Its structure enables it to carry out many important functions in the body.
Water molecules are charged, with the oxygen atom being slightly negative and the hydrogen atoms being slightly positive. These opposite charges attract each other, forming hydrogen bonds. These are weak, long distance bonds that are very common and very important in biology.
Water has a number of important properties essential for life. Water has many important properties due to the fact that there are hydrogen bonds in its structure. For example, because water is charged, it is a very good solvent. Charged or polar molecules such as salts, sugars, amino acids dissolve readily in water and so are called hydrophilic ("water loving"). Uncharged or non-polar molecules such as lipids do not dissolve so well in water and are called hydrophobic ("water hating"). This means water can transport substances very easily and efficiently throughout the body. Water is miscible with many liquids, such as ethanol, in all proportions, forming a single homogeneous liquid. For example, when a large amount of alcohol is drunk, to reduce the harmful effects of it, water mixes with the ethanol to reduce its concentration and harmful effects on the body.
Water also has high adhesion properties because of its polar nature. In biological cells and organelles, water is in contact with membrane and protein surfaces that are hydrophilic; that is, surfaces that have a strong attraction to water. The scientist Irving Langmuir observed a strong repulsive force between hydrophilic surfaces. To dehydrate hydrophilic surfaces—to remove the strongly held layers of water of hydration—requires doing substantial work against these forces, called hydration forces. These forces are very large but decrease rapidly over a nanometre or less. They...
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