TNA molecule. Computer artwork of threose nucleic acid (TNA). TNA is a synthetic molecule structurally similar to deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). It has a sugar- phosphate backbone composed of a four-carbon sugar called threose. DNA and RNA contain five-carbon ribose molecules. The yellow lines indicate molecular shape. It is believed that TNA was a precursor to RNA and DNA on early Earth. Synthetic biology researchers are using TNA to create novel, genetically altered cells. TNA was first synthesised by Albert Eschenmoser at the Scripps Research Institute, California, USA.