Human Physiology   7/e   Vander/Sherman/Luciano
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Chapter 2: Chemical Composition of the Body


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Chapter 2: Chemical Composition of Body

  1. ATOMS

    1. Atoms are composed of three subatomic particles: positive protons and neutral neutrons, both located in the nucleus, and negative electrons revolving around the nucleus.
    2. The atomic number is the number of protons in an atom and because atoms are electrically neutral, it is also equal to the number of electrons.
    3. The atomic weight of an atom is the ratio of the atom's mass relative to that of a carbon-12 atom.
    4. One gram atomic mass is the number of grams of an element equal to its atomic weight. One gram atomic mass of any element contains the same number of atoms - 6 x l023.
    5. There are 24 elements essential for normal body function.

  2. MOLECULES

    1. Molecules are formed by linking atoms together.
    2. A covalent bond is formed when two atoms share a pair of electrons. Each type of atom can form a characteristic number of covalent bonds: hydrogen forms one, oxygen two, nitrogen three, and carbon four.
    3. Molecules have characteristic shapes, which can be altered within limits by the rotation of their atoms around covalent bonds.

  3. IONS

    1. When an atom gains or loses one or more electrons, it acquires a net electric charge and becomes an ion.

  4. FREE RADICALS

    1. Free radicals are atoms or molecules that contain atoms that have an unpaired electron in their outer electron orbital.

  5. POLAR MOLECULES

    1. In polar covalent bonds, one atom attracts the bonding electrons more than the other atom does.
    2. The electrical attraction between hydrogen and the oxygen or nitrogen atom in a separate molecule or different region of the same molecule forms a hydrogen bond.
    3. Water, a polar molecule, is attracted to other water molecules by hydrogen bonds.

  6. SOLUTIONS

    1. Substances dissolved in a liquid are solutes, and the liquid in which they are dissolved is the solvent. Water is the most abundant solvent in the body.
    2. Substances that have polar or ionized groups dissolve in water by being electrically attracted to the polar water molecules.
    3. In water, amphipathic molecules form clusters with the polar regions at the surface and the nonpolar regions in the interior of the cluster.
    4. The molecular weight of a molecule is the sum of the atomic weights of all its atoms. One mole of any substance is its weight in grams equal to its molecular weight and contains 6 x10 molecules.
    5. Substances that release a hydrogen ion in solution are called acids. Those that accept a hydrogen ion are bases.

      1. The acidity of a solution is determined by its free hydrogen ion concentration; the greater the hydrogen ion concentration, the greater the acidity.
      2. The pH of a solution is the negative logarithm of the hydrogen ion concentration. As the acidity of a solution increases, the pH decreases. Acid solutions have a pH less than 7.0 whereas alkaline solutions have a pH greater than 7.0.

  7. CLASSES OF ORGANIC MOLECULES

    1. Carbohydrates are composed of carbon, hydrogen, and oxygen in the proportions Cn(H2O)n.

      1. The presence of the polar hydroxyl groups makes carbohydrates soluble in water.
      2. The most abundant monosaccharide in the body is glucose (C6H1206), which is stored in cells in the form of the polysaccharide glycogen.

    2. Lipids lack polar and ionized groups, a characteristic that makes them insoluble in water.

      1. Triacylglycerols (fats) are formed when fatty acids are linked to each of the three hydroxyl groups in glycerol.
      2. Phospholipids contain two fatty acids linked to two of the hydroxyl groups in glycerol, with the third hydroxyl linked to phosphate, which in turn is linked to a small charged or polar compound. The polar and ionized groups at one end of phospholipids make these molecules amphipathic.
      3. Steroids are composed of four interconnected rings, often containing a few polar hydroxyl groups.

    3. Proteins, macromolecules composed primarily of carbon, hydrogen, oxygen, and nitrogen, are polymers of 20 different amino acids.

      1. Amino acids have an amino (CNH2) and a carboxyl (CCOOH) group linked to their terminal carbon atom.
      2. Amino acids are linked together by peptide bonds between the carboxyl group of one amino acid and the amino group of the next.
      3. The primary structure of a polypeptide chain is determined by (1) the number of amino acids in sequence, and (2) the type of amino acid at each position.
      4. The factors that determine the conformation of a polypeptide chain are hydrogen bonds, ionic bonds, weak van der Waals forces, and covalent bonds.
      5. Hydrogen bonds between peptide bonds along a polypeptide chain force much of the chain into an alpha helix.
      6. Covalent disulfide bonds can form between the sulfhydryl groups of cysteine side chains to hold regions of a polypeptide chain close to each other.
      7. Some proteins have multiple polypeptide chains.

    4. Nucleic acids are responsible for the storage, expression, and transmission of genetic information.

      1. Deoxyribonucleic acid (DNA) stores genetic information.
      2. Ribonucleic acid (RNA) is involved in the decoding of the information coded in DNA into instructions for linking amino acids together to form proteins.
      3. Both types of nucleic acid are polymers of nucleotides, each containing a phosphate group, a sugar, and a base of carbon, hydrogen and nitrogen atoms.
      4. DNA contains the sugar deoxyribose and consists of two chains of nucleotides coiled around each other in a double helix. The chains are held together by hydrogen bonds between purine and pyrimidine bases in the two chains.
      5. Base pairings in DNA always occur between guanine and cytosine and between adenine and thymine.
      6. RNA consists of a single chain of nucleotides, containing the sugar ribose and three of the four bases found in DNA. The fourth base is the pyrimidine uracil rather than thymine. Uracil base-pairs with adenine.

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