Proteins, the bulk of the solid matter of cells, get their name from the Greek "proteios" for primary. They are the principal material of skin, muscle, tendons, nerves, blood, enzymes, antibodies, and many hormones. Some proteins, such as the hemoglobin that carries oxygen in red blood cells, are involved in transport and storage. Others, like insulin, are hormones, the chemical messengers that coordinate body activities. Immunoglobulins, also proteins, are the master molecules of immunity. The enzymes that are the catalysts for body processes — they can increase the speed of a chemical reaction more than a millionfold — are also proteins.

DNA contains the genes that control the structure and functioning of the body. It is made of alternating deoxyribose and phosphoric acid molecules, which combine to form a chain. Four "bases" — adenine, thymine, guanine, and cytosine or A, T, G and C — are attached to this chain, each linking to a deoxyribose unit. The sequence of bases along the DNA molecule forms a coded message that tells the cell how to manufacture protein. Your DNA, unless you are an identical twin, is distinct from everyone else's. The difference is in the order of the bases.