CooperCh2Cell - 1 G. M. Cooper, The Cell: A Molecular...

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Unformatted text preview: 1 G. M. Cooper, The Cell: A Molecular Approach NIH Bookshelf url http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=books Ch. 2. The Molecular Composition of Cells Table of Contents Carbohydrates 4 Lipids (more detail at end) 7 Nucleic acids (more detail to come) 14 Proteins (more detail to come) 18 Cell Membranes 27 2 ] Cells are composed of water, inorganic ions, and carbon-containing (organic) molecules. Water is the most abundant molecule in cells, accounting for 70% or more of total cell mass. Consequently, the interactions between water and the other constituents of cells are of central importance in biological chemistry. The critical property of water in this respect is that it is a polar molecule , in which the hydrogen atoms have a slight positive charge and the oxygen has a slight negative charge (Figure 2.1 ). Figure 2.1. Characteristics of water (A) Water is a polar molecule, with a slight negative charge ( - ) on the oxygen atom and a slight positive charge ( + ) on the hydrogen atoms. Because of this polarity, water molecules can form hydrogen bonds (dashed lines) either with each other or with other polar molecules (B), in addition to interacting with charged ions (C). Because of their polar nature, water molecules can form hydrogen bonds with each other or with other polar molecules, as well as interacting with positively or negatively charged ions. As a result of these interactions, ions and polar molecules are readily soluble in water ( hydrophilic ). In contrast, nonpolar molecules , which cannot interact with water, are poorly soluble in an aqueous environment ( hydrophobic ). Consequently, nonpolar molecules tend to minimize their contact with water by associating closely with each other instead. As discussed later in this chapter, such interactions of polar and nonpolar molecules with water and with each other play crucial roles in the formation of biological structures, such as cell membranes. The inorganic ions of the cell, including sodium (Na + ), potassium (K + ), magnesium (Mg 2+ ), calcium (Ca 2+ ), phosphate (HPO 4 2- ), chloride (Cl- ), and bicarbonate (HCO 3- ), constitute 1% or less of the cell mass. These ions are involved in a number of aspects of cell metabolism, and thus play critical roles in cell function. It is, however, the organic molecules that are the unique constituents of cells. Most of these organic compounds belong to one of four classes of molecules: carbohydrates, lipids, proteins, and nucleic acids . Proteins, nucleic acids, and most carbohydrates (the polysaccharides) are macromolecules formed by 2 ] Cells are composed of water, inorganic ions, and carbon-containing (organic) molecules. Water is the most abundant molecule in cells, accounting for 70% or more of total cell mass. Consequently, the interactions between water and the other constituents of cells are of central importance in biological chemistry. The critical property of water in this respect is that it is a polar molecule , in which the hydrogen atoms have a slight positive charge and the...
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This note was uploaded on 03/04/2011 for the course CHM 327 taught by Professor Jay during the Spring '08 term at Cal Poly Pomona.

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CooperCh2Cell - 1 G. M. Cooper, The Cell: A Molecular...

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