Syn and anti nucleosides

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The objective of this article is to highlight aspects of the 3D structure of nucleosides, but there are links to more general descriptions of nucleosides and nucleotides available in the External Links section.

Contents 1 Purine Nucleosides 2 Pyrimidine Nucleosides 3 Examples of Nucleotides 4 Additional Resources 5 External Links

Purine Nucleosides

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Adenosine () is composed of an adenine bonded to a furanose by a (colored green). Observe that the adenine ring is nearly perpendicular to the furanose ring, but projecting away from the furanose (anti conformation). Without hinderance from groups on either ring the adenine ring can rotate about the glycosidic bond, and form the . The two common purines, adenine and guanine, can rotate between the anti and syn conformations, but the anti configuration is favored. Compare the contact present between the two rings in these two spacfilling representations, and . Even though the anti conformation is favored with the purines the syn configuration can be formed and actually has a role in the formation of the Z-DNA, a conformation of DNA double helix.

Groups on the ribofuranose, such as the on the 2' carbon, sterically hinder the rotation of the adenine about the glycosidic bond. This lack of ability to rotate results in two possible configurations. The anti configuration, which you are now viewing, but shows the hinderance more realistically. and the , , same view but in .

Pyrimidine Nucleosides

of uridine in the anti conformation. of cytidine in the syn conformation. oxygen at the C-2 position of cytidine invading the space of both hydrogen at C-2' and the oxygen of the furanose ring. Since both pyrimidines found in DNA have an oxygen at the C-2 position, nucleosides and nucleotides of these pyrimidines only adopt the anti conformation and therefore can not be part of Z-DNA.

Examples of Nucleotides

AMP ;

UMP ;

cAMP ;

Additional Resources

For additional information, see: Nucleic Acids

External Links

• nucleosides
• nucleotides.