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ARKive : endangered species Wildscreen's Arkive project was launched in 2003 and grew to become the world's biggest encyclopaedia of life on Earth. With the help of over 7,000 of the world’s best wildlife filmmakers and photographers, conservationists and scientists, Arkive.org featured multi-media fact-files for more than 16,000 endangered species. Freely accessible to everyone, over half a million people every month, from over 200 countries, used Arkive to learn and discover the wonders of the natural world. Since 2013 Wildscreen was unable to raise sufficient funds from trusts, foundations, corporates and individual donors to support the year-round costs of keeping Arkive online. Therefore, the charity had been using its reserves to keep the project online and was unable to fund any dedicated staff to maintain Arkive, let alone future-proof it, for over half a decade. Therefore, a very hard decision was made to take the www.arkive.org website offline in February 2019.

ATDbio.com Contents 2′-Deoxyribonucleic acid (DNA) DNA (2′-deoxyribonucleic acid) is the molecular store of genetic information in nearly all living systems. It is a large polymeric molecule composed of monomers known as nucleotides. Each nucleotide consists of a heterocyclic base, a pentose sugar (2′-deoxy-d-ribofuranose), and a phosphate group. Figure 1 | Chemical structures of the heterocyclic bases of DNA Adenine and guanine are purines and cytosine and thymine are pyrimidines (Figure 2). Figure 2 | Structures of the purine and pyrimidine heterocyclic ring systems The deoxyribose sugar is shown in Figure 3. Figure 3 | Mutarotation of 2′-deoxy-D-ribose allows interconversion between furanose, acyclic and pyranose forms The phosphate group can be found at the 5′- or 3′-position of the sugar depending on the method used to break down DNA to produce the nucleotides. Figure 4 | Structures of a deoxynucleoside and a deoxynucleotide Figure 5 | Structures of syn and anti nucleoside conformations See also