DNA. Computer artwork of part of a molecule of DNA (deoxyribonucleic acid). This is the molecule that is responsible for heredity, growth and development. It comprises two sugar-phosphate strands (purple) linked by pairs of bases (yellow balls and sticks). There are four bases: adenine, thymine, guanine and cytosine. Adenine only joins to thymine, and guanine only links with cytosine. This means that each strand is complementary to the opposite one. DNA carries information as the sequence of bases along a strand. The strands contain specific regions called genes, which hold the recipes for proteins, the building blocks of the body.