View source for Syn and anti nucleosides

<StructureSection load='Adenosine.pdb' size='450' side='right' scene='Syn_and_anti_nucleosides/First_view/1' caption=''>
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.

== Purine Nucleosides ==
 
Adenosine (<scene name='Syn_and_anti_nucleosides/First_view/1'>Reset Initial scene</scene>) is composed of an adenine bonded to a furanose by a <scene name='Syn_and_anti_nucleosides/Glycosidic_bond/1'>β glycosidic bond</scene> (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 <scene name='Syn_and_anti_nucleosides/Syn-conformation/1'>syn conformation</scene>.  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, <scene name='Syn_and_anti_nucleosides/Anti-conformation2/1'>anti conformation</scene> and <scene name='Syn_and_anti_nucleosides/Syn-conformation2/1'>syn conformation</scene>. 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.
  
== Pyrimidine Nucleosides ==
<scene name='Syn_and_anti_nucleosides/Anti-uridine/1'>View</scene> of uridine in the anti configuration, the oxygen on <font color=orange>C-2</font> of uridine is projecting away from the furanose ring.  <scene name='Syn_and_anti_nucleosides/Syn-cytidine/1'>View</scene> of cytidine in the syn configuration, the oxygen on <font color=orange>C-2</font> is projecting toward the furanose ring.  This oxygen at the <font color=orange>C-2</font> position produces significant hinderance to the rotation of the pyrimidine about the glycosidic bond as shown in this <scene name='Syn_and_anti_nucleosides/Syn-cytidine2/1'>scene</scene>. The oxygen doubled bonded to the <font color=orange>C-2</font> invades the space of the hydrogen at C-2' and to a lesser extent 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.

== 3D Images of Nucleotides ==
AMP <scene name='Syn_and_anti_nucleosides/Amp/1'>as ball and stick</scene>; <scene name='Syn_and_anti_nucleosides/Amp2/1'>as spacefill</scene>

UMP <scene name='Syn_and_anti_nucleosides/Ump/1'>as ball and stick</scene>; <scene name='Syn_and_anti_nucleosides/Ump2/1'>as spacefill</scene>

cAMP <scene name='Syn_and_anti_nucleosides/Camp/1'>as ball and stick</scene>; <scene name='Syn_and_anti_nucleosides/Camp2/1'>as spacefill</scene>

For additional functions of nucleotides, see: [[Nucleic Acids]]
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== External Links ==
*[http://en.wikipedia.org/wiki/Nucleoside nucleosides]
*[http://en.wikipedia.org/wiki/Nucleotide nucleotides].