Illustration of part of a strand of DNA (deoxyribonucleic acid), featuring labeled base pairs. The DNA molecule has a double helix arrangement, being composed of two righthanded spiral strands of sugar phosphates. These strands are held together by complementary pairs of four crosslinking nucleotide bases (colored rods): adenine, cytosine, guanine and thymine. The sequence of bases makes up the unique genetic code of every individual organism.
