International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by M. G. Rossmann and E. Arnold

© International Union of Crystallography 2006
International Tables for Crystallography (2006). Vol. F. ch. 23.3, p. 595   | 1 | 2 |

Figure 23.3.2.13 

R. E. Dickersona*

a Molecular Biology Institute, University of California, Los Angeles, Los Angeles, CA 90095–1570, USA
Correspondence e-mail: red@mbi.ucla.edu

[Figure 23.3.2.13]
Figure 23.3.2.13

Syn versus anti orientation about the glycosyl bond connecting sugar and base. Right: anti conformation, with χ ca 210°. Left: syn conformation, with χ around 60°. Both A- and B-DNA only employ the anti geometry; Z-DNA uses anti for pyrimidines and syn for purines, as shown here. Note that the 5′-to-3′ direction in both rings is down into the paper. Hence, antiparallel backbone chains can be achieved only by a zigzag chain geometry with local chain reversals, as shown later in Fig. 23.3.3.4[link]. Black dots labelled A, B and Z indicate the position of the helix axis relative to the base pairs in A-, B- and Z-DNA.