Proteopedia Entry: Deoxyribonucleic Acid (DNA)*

This Proteopedia page presents a model of deoxyribonucleic acid in its most common form—B-DNA. The structure (Fig. 1, left) shows the DNA double helix with the two complementary strands, each containing 10 nucleotides, running in an antiparallel fashion. The page provides interactive green links that allows the viewers to visualize and explore several key features of a DNA duplex. The coiling of two single strands of DNA around each other to form a double helix is illustrated by highlighting one strand of duplex DNA and fading away its corresponding complementary strand. One of the interactive green links deconstructs a nucleotide into its corresponding components—a 5′ phosphorylated sugar and a nitrogenous base. The page allows the users to interact with the imino/enol and the amino/keto tautomers of a nitrogenous base and demonstrates the importance of the amino/keto form. The page explains the complementary base pairing that exists in a double stranded DNA molecule, and as shown in Fig. 1 (middle) displays the Watson–Crick base pairing between adenine–thymine and cytosine–guanine. The viewer can clearly see the three hydrogen bonds between cytosine–guanine and the two hydrogen bonds between adenine–thymine from different perspectives. A key highlight of the page is the representation of DNA in its surface form (Fig. 1, right) wherein one can clearly visualize the two different grooves in a DNA molecule. The users can also look at the asymmetric positioning of beta-glycosyl bonds of the nitrogenous bases, which give rise to the major and minor grooves in a DNA molecule. Three-dimensional structure of DNA. (Left) The double helical form of B-DNA, (middle) “Watson–Crick” base pairing, and (right) surface representation of DNA showing the major and minor grooves. The DNA double helix is also found in the A- and Z-forms. These three DNA double helices are shown interactively and compared on the Proteopedia page “Forms of DNA” at http: //www. proteopedia. org/w/FormsₒfDNA.