-H-N or N-H-O.In April 1953 Watson and Crick published their structure - the now famous double helix. This brilliant accomplishment ranks as one of the most significant discoveries in science because it led the way to an understanding of genetics in terms of the molecules involved. In 1962 they received the Nobel prize for Medicine in recognition of this achievement, along with Maurice Wilkins of Kings College London who had performed the initial X-ray crystallography studies. A very small section of DNA showing the double helix structure linked by bases, like the rungs on a twisted ladder.(Click here or on the image to get 3D structure in Molfile format).(Click here to get an interactive 3D structure in pdb format - requires Chime). Bases, Nucleotides and NucleosidesIn every living cell there are found nucleoproteins - substances made up of proteins combined with natural polymers, the nucleic acids. Where the backbone of a protein molecule is a polyamide (or polypeptide) chain, the backbone of a nucleic acid molecule is a polyester chain (called a polynucleotide chain). The ester is derived from phosphoric acid (the acid portion) and a sugar (the alcohol portion). Polynucleotide chainThe sugar is D-ribose, which is in the group of nucleic acids called ribonucleic acids (RNA), and D-2-deoxyribose forms the basis of DNA. The 2-deoxy simply indicates the lack of an -OH group at the 2 position. Thus DNA stands for deoxyribonucleic acid.Attached to the carbon at one side of the sugar is one of the 4 bases, A, C, G, or T. The base-sugar unit is called a nucleoside. Attached to the other side of the sugar is a phosphoric acid unit, linking the nucleoside to the neighbouring sugar. The base-sugar-phosphoric acid unit is called a nucleotide.Adenosine, a nucleotide containing adenine (red), deoxyribose (black) and phosphoric acid (blue).The 3D molfiles of all of the 4 nucleotides can be obtained here: A, C, G, T.Two of these polyn...
