Forms of DNA

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	=== Helical Parameters of the three forms of DNA ===		=== Helical Parameters of the three forms of DNA ===

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Revision as of 20:29, 7 February 2018

See DNA - History of the discovery and current applications (Hebrew)

See Also: DNA and Z-DNA

Contents 1 A comparative representation of the three forms of DNA 2 Helical Parameters of the three forms of DNA 3 Structural Transformation between A and B DNA 4 References

A comparative representation of the three forms of DNA

Sources^[1]

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A-DNA	B-DNA	Z-DNA
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Helical Parameters of the three forms of DNA

DNA is a very flexible molecule and has the ability to exist in various forms based on the environmental conditions. Naturally occurring DNA double helices are classified into A, B and Z-types. A and B-forms of DNA are the right handed forms whereas Z-DNA is the left handed form. When hydrated the DNA generally assumes B-form. The A conformation is found when there is little water to interact with the helix and is also the conformation adopted by the RNA. The formation of Z-DNA occurs with the methylation of deoxycytosine residues and also during transcription where negative supercoiling stabilizes it.

Parameter	A-DNA	B-DNA	Z-DNA
Helix sense	right-handed	right-handed	left-handed
Residues per turn	11	10.5	12
Axial rise [Å]	2.55	3.4	3.7
Helix pitch(°)	28	34	45
Base pair tilt(°)	20	−6	7
Rotation per residue (°)	33	36	-30
Diameter of helix [Å]	23	20	18
Glycosidic bond configuration dA,dT,dC dG	anti anti	anti anti	anti syn
Sugar pucker dA,dT,dC dG	C3'-endo C3'-endo	C2'-endo C2'-endo	C2'-endo C3'-endo
Intrastrand phosphate-phosphate distance [Å] dA,dT,dC dG	5.9 5.9	7.0 7.0	7.0 5.9
Sources:[2][3][4]

Structural Transformation between A and B DNA

Morph Sources ^[5] / Morphs

References

1. ↑ http://203.129.231.23/indira/nacc/
2. ↑ Rich A, Nordheim A, Wang AH. The chemistry and biology of left-handed Z-DNA. Annu Rev Biochem. 1984;53:791-846. PMID:6383204 doi:http://dx.doi.org/10.1146/annurev.bi.53.070184.004043
3. ↑ Wang AH, Quigley GJ, Kolpak FJ, Crawford JL, van Boom JH, van der Marel G, Rich A. Molecular structure of a left-handed double helical DNA fragment at atomic resolution. Nature. 1979 Dec 13;282(5740):680-6. PMID:514347
4. ↑ Sinden, Richard R (1994-01-15). DNA structure and function (1st ed.). Academic Press. pp. 398. ISBN 0-12-645750-6.
5. ↑ Krebs WG, Gerstein M. The morph server: a standardized system for analyzing and visualizing macromolecular motions in a database framework. Nucleic Acids Res. 2000 Apr 15;28(8):1665-75. PMID:10734184