Genetic research. Conceptual computer artwork showing part of a DNA molecule (down left) and a molecule of thrombin (lower left). Thrombin is an enzyme that acts on fibrinogen in blood causing it to clot. DNA (deoxyribonucleic acid) is a double helix molecule that carries the genetic code, which controls and transmits an organism's hereditary traits. DNA is made up of two strands of sugar-phosphate groups. The strands twist to form the double helix shape, and are cross-linked by complementary pairs of nucleotide bases (horizontal links). The sequence of base pairs, arranged in discrete segments known as genes, determines the genetic code.