Bio1151 Chapter 4 Carbon and the Molecular Diversity of Life
  1. Living organisms are made up of          compounds based mostly on the element carbon, which has       valence electrons, and can form four covalent bonds with other atoms.

      Valence is the number of covalent bonds an atom can form. It is usually equal to the number of electrons required to complete the atom's outermost (valence) electron shell. Carbon has a valence of 4 and can form many types of large molecules.

      These hydrocarbons (molecules consisting only of carbon and hydrogen) illustrate the diversity of the carbon skeletons of organic molecules. Exercise:
  2. Fats contain              tails composed of only         and           atoms.

      Fats contain hydrocarbons (molecules consisting of only carbon and hydrogen). Mammalian adipose cells are almost filled by high-energy fat molecules which serve as fuel reserves. A fat molecule consists of a glycerol molecule joined to 3 hydrocarbon tails, which are nonpolar and hydrophobic. (black = C; gray = H; red = O)
  3. Some organic compounds occur as          with the same molecular formula but different             .

      Isomers are compounds with the same molecular formula but different structures and properties.

    • Structural isomers differ in the arrangement of their covalent bonds.
    • Geometric isomers differ in their spatial arrangements around a double bond.
    • Enantiomers (stereo isomers) are mirror images of each other and contain an asymmetric carbon.


      Structural isomers such as pentane and 2-methyl butane (isopentane) differ in covalent partners.

      Geometric isomers differ in arrangement about a double bond. Cis isomers have large components on the same side relative to the double bond. Trans isomers have large components on opposite sides.

      Enantiomers (stereo isomers), such as the isomers of dopa, differ in spatial arrangement around an asymmetric carbon which is attached to four different groups.
      These isomers are mirror images, like left and right hands.
  4.             groups are the chemically reactive groups of atoms that give          molecules distinctive chemical properties.

      Functional groups.

      1. hydroxyl

      2. carbonyl

      3. carboxyl

      4. amino

      5. sulfhydryl

      6. phosphate
        • ATP
      7. methyl

      In a hydroxyl group (-OH), a hydrogen atom is bonded to an oxygen atom, which in turn is bonded to the carbon skeleton of the organic molecule.

      The electronegative oxygen atom confers polar (and hydrophilic) properties to this group.

      Do not confuse this functional group with the hydroxide ion, OH^- .

      The carbonyl group (-C=O) consists of a carbon atom joined to an oxygen atom by a double bond.

      Ketones have the carbonyl group within a carbon skeleton. Aldehydes have the carbonyl group at the end of the carbon skeleton.

      The carboxyl group (-COOH) contains a carbon atom double-bonded to an oxygen atom and is also bonded to a hydroxyl group. The electronegative oxygen atom can dissociate the hydrogen ion (H^+), making the group acidic and polar.

      The amino group (-NH[2]) consists of a nitrogen atom bonded to 2 hydrogen atoms.

      The nitrogen atom tends to be basic and confers polar properties to this group.

      Amino acids, which make up proteins, contain both an amino and a carboxyl group.

      The sulfhydryl group (-SH) consists of a sulfur atom bonded to a hydrogen atom.

      A major role played by this group is stabilizing protein structure.

      A phosphate group contains a phosphorus atom bonded to 4 oxygen atoms; two of the oxygens usually lose their hydrogen atoms and become negatively charged. Phosphate groups are components of nucleotides and also are sources of energy in the form of ATP.

      ATP (Adenosine TriPhosphate) is an important energy molecule with 3 phosphate groups. The terminal phosphate group can split off to form ADP (Adenosine DiPhosphate) and inorganic phosphate. This reaction releases energy that can be used by the cell.

      The methyl group (-CH[3]) consists of a carbon atom bonded to 3 hydrogen atoms.

      The weak electronegativity of the carbon atom makes this group nonpolar and hydrophobic.

      Female (estradiol) and male (testosterone) sex hormones.

      The two steroid molecules differ only in the functional groups attached to 4 fused rings.

      These subtle variations influence the developmental differences between female and male vertebrates.