Conformation of DNA

The importance of the role of DNA in the genetic code has focused research on the structure of the active compound and the overall conformation of DNA as a receptor. In addition the identification of benzola]pyrene as an important carcinogen (27) has stimulated extensive research to determine the origin and its activity. 

The structures shown in Fig. 4-1 are for B-form DNA, the usual form of the molecule in solution. Different double-helical DNA structures can be formed by rotating various bonds that connect the structure. These are termed different conformations. The A and B conformations are both right-handed helices that differ in pitch (how much the helix rises per turn) and other molecular properties. Z-DNA is a left-handed helical form of DNA in which the phosphate backbones of the two antiparallel DNA strands are still arranged in a helix but with a more irregular appearance. The conformation of DNA (A, B, or Z) depends on the temperature and salt concentration as well as the base composition of the DNA. Z-DNA appears to be favored in certain regions of DNA in which the sequence is rich in G and C base pairs. 

The conformation of DNA that predominates within the cell (known as B-DNA) is shown schematically in Fig. A2 and as a van der Waals model in Fig. B1. In the schematic diagram (A2), the deoxyribose-phosphate backbone is shown as a ribbon. The bases (indicated by lines) are located on the inside of the double helix. This area of DNA is therefore apolar. By contrast, the molecule s surface is polar and negatively charged, due to the... 

The illustration opposite shows selected nucleic acid molecules. Fig. A shows various conformations of DNA, and Fig. B shows the spatial structures of two small RNA molecules. In both, the van der Waals models (see p. 6) are accompanied by ribbon diagrams that make the course of the chains clear. In all of the models, the polynucleotide backbone of the molecule is shown in a darker color, while the bases are lighter. 

CD spectra provide the most conventional diagnosis for the conformations of DNA and RNA in solution. Figures 26, 27, and 28 indicate typical CD properties of A, B,... 

The detection of different conformations of DNA underscores the inherent flexibility built into the DNA duplex. All the conformations discussed thus far involve regular linear duplexes. Energetically favorable interactions with other molecules, particularly proteins, can induce additional conformations that do not result in major changes in either pair-... 

Novakova O, Kasparkova J, Bursova V, Hoff C, Vojtiskova M, Chen H, Sadler PJ, Brabec V (2005) Conformation of DNA modified by monofunctional Ru(II) arene complexes recognition by DNA binding proteins and repair. Relationship to cytotoxicity. ChemBiol 12 121-129... 

DNA s secondary structure is a helix (Figure 16.1) twisted to the right and known as the DNA B form. The distance between two consecutive bases is 3.4 A. Since the helix repeats itself approximately every 10 bases, the pitch per turn of the helix is 33.4 A. B DNA is the major conformation of DNA in solution. 

An alternative conformation of the B DNA appears in solution when the amount of water necessary to hydrate the double helix is not sufficient. In the A conformation, the pitch is 24.6 A, and a complete turn of the helix needs the presence of 11 base pairs. Finally, we should add that in vivo, we do not know whether the A form of DNA does really exist. The third conformation of DNA is the Z form where the helix is twisted toward the left. 

Sanger develops his sequence analysis for amino acids in proteins Nobel Prize Chemistry to Hermann Staudinger for contributions to the understanding of macromolecular chemistry Watson and Crick discover the double helix conformation of DNA, the break-through in bio-polymer science... 

In 1953, James D. Watson and Francis C. Crick used X-ray diffraction patterns of DNA fibers to determine the molecular structure and conformation of DNA. They found that DNA contains two complementary polynucleotide chains held together by hydrogen... 

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