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In water, the water molecules act to exclude them. The nonpolar molecules are forced into association with one another, thus minimizing their disruption of the hydrogen bonding of water. In effect, they shrink from contact with water and for this reason they are referred to as hydrophobic (Greek hydros, “water” and phobos, “fearing”). In contrast, polar molecules, which readily form hydrogen bonds with water, are said to be hydrophilic (“water-loving”). The tendency of nonpolar molecules to aggregate in water is known as hydrophobic exclusion.

Many scientists believe amino acids were among the first molecules formed in the early earth. It seems highly likely that the oceans that existed early in the history of the earth contained a wide variety of amino acids. Amino acid — Amino Acids Are the Building Blocks of Proteins H O H O H2O Amino Acid Structure An amino acid is a molecule containing an amino group (—NH2), a carboxyl group (—COOH), and a hydrogen atom, all bonded to a central carbon atom: Each amino acid has unique chemical properties determined by the nature of the side group (indicated by R) covalently bonded to the central carbon atom.

This micrograph, with sketch below, shows a section of DNA magnified a million times! The molecule is so slender that it would take 50,000 of them to equal the diameter of a human hair. “Seeing” DNA DNA molecules cannot be seen with an optical microscope, which is incapable of resolving anything smaller than 1000 atoms across. An electron microscope can image structures as small as a few dozen atoms across, but still cannot resolve the individual atoms of a DNA strand. 12). How do these microscopes work?