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Forms of DNA

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See Also: DNA and Z-DNA

Contents

A comparative representation of the three forms of DNA

Sources[1]

A-DNA

B-DNA

Z-DNA

Synchronize the three applets showing A-, B- and Z-DNA by clicking the checkbox

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

Proteopedia Page Contributors and Editors (what is this?)

Adithya Sagar, Eran Hodis, Eric Martz

DOI: http://dx.doi.org/10.14576/438459.1419971 (?)
Citation: Hodis E, Sagar A, Martz E, 2012, "Forms of DNA", Proteopedia, DOI: http://dx.doi.org/10.14576/438459.1419971
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