View source for A-RNA tour

==A-form RNA==
<StructureSection load='1rna' size='350' side='right' caption='A-RNA [[1rna]]' scene='72/725869/A-rna_overview/1'>
Source <ref>PMID:7071593</ref>
== Structural highlights ==
<UL>
<LI> Most RNA and RNA-DNA duplex in this form
<LI> Shorter, wider helix than B.
<LI> Deep, narrow major groove not easily accessible to proteins
<LI> Wide, shallow minor groove accessible to proteins, but lower information content than major groove.
<LI> Favored conformation at low water concentrations
<LI> Base pairs tilted to helix axis and displaced from axis
<LI> Sugar pucker C3'-''endo'' (in RNA 2'-OH inhibits C2'-''endo'' conformation)
</UL>

== Take the Tour ==

The tour starts with the <scene name='72/725869/A-rna_overview/1'>Default</scene> view. Now look at this <scene name='72/725869/Rna_space_filling_view/2'>space filling view</scene>.The backbone is yellow and the bases are magenta. Note that the major groove (at the top, when you have just clicked the button) is very deep.

Now change the display to make the show the <scene name='72/725869/Rna_space_filling_bbone/1'>sugar-phosphate backbone as pseudo-bonds</scene> connecting the phosphate atoms.  Now the bases are easier to see. Notice how they are stacked upon each other but not perpendicular to the axis of the double helix. They are also displaced to the side of the axis. The result is a wide, short helix. Note also that the backbone forms a smooth, continuous curve.

You can <scene name='72/725869/Zoom_pairs/1'>look at just four of the base pairs.</scene>.You are looking into the major groove and the colors of the base pairs alternate. You can also <scene name='72/725869/Zoom_pairs_only/1'>look at just the bases</scene>.
Each base pair stacks on the next similarly, as shown from <scene name='72/725869/Zoom_pairs_top/1'>this top view</scene>. This is the <scene name='72/725869/Zoom_pairs_only_top/1'>same top view of just the bases</scene>.  
B-DNA stacks similarly, but compare this with Z-DNA, which behaves much differently.  Essentially all helical RNA is in A form, but DNA can also be found in A form under certain conditions (particularly in RNA-DNA hybrids). The 2'-OH of ribose  favors the C3'-''endo'' sugar pucker necessary for A-form geometry. The O2' is easily seen as white spheres in <scene name='72/725869/Rna_space_filling_o2prime/1'>this space fill view</scene>.

You can compare it with the DNA forms by looking at this [[Media:JnABZ3d.gif|3D red-blue stereo picture of A, B, and Z DNA]]
</StructureSection>
==See Also==
* My [[Z-DNA model tour]]
* My [[B-DNA tour]]
* My [[Transfer RNA tour]]
* [[Z-DNA]]
* A more general overview will be found at [[DNA]].
* [[Forms of DNA]] shows a side-by-side comparison of A, B, and Z forms of DNA.
* An interactive tutorial on [http://dna.molviz.org DNA Structure], ''disponible también en español'' and eight other languages.
== References ==

JSmol in Proteopedia <ref>DOI 10.1002/ijch.201300024</ref> or to the article describing Jmol <ref>PMID:21638687</ref> to the rescue.


<references />