Poly deoxy nucleotide

Fig. 6. P-NMR spectra at 109.3 MHz of sonicated alternating purine-pyrimidine deoxy-nucleotide duplexes A, poly(dAdT)-poly(dAdT) at 24 °C B, poly(dA-br dU)-prfy(dA-br dU) at 30X C, poly(dAdU) poly(dAdU) at 3I C D, poly(dIdC)-poly(dIdC) at 39 C E, poly(dGdC) poly(dGdC)at23 C allin0.1 MNaQand0.05 mAfEDTA,pH6-7,except(B) in S toM Tris and 0.1 laM EDTA. Chemical shifts arc upiield positive from internal TMP. Reproduced with permission, fiom Cohen et al., 1981. Copyright 1981 American Chemical Society.

DNA (Table 1.2) (Figure 1.74). The helbc sense of Z-form DNA is now left handed and the backbones of the two poly deoxynucleotide chains map out a zigzag spiral path. This results from the tendency of deoxyguanosine nucleotide residues to distort so that their 2 -deoxy-/3-D-ribofuranose rings adopt a C -endo instead of C -endo twist conformation (Figure 1.71). However, in addition, the guanine bases move to a syn conformation (positioned over the top of their attached furanose rings), instead of the more usual anti conformation... 

The two types of natural polynucleotides (nucleic acids) are classified according to the sugars they contain. Ribonucleic acid (RNA) contains exclusively P-o-ribose, while the sugar in deoxyribonucleic acid (DNA) is P-2-deoxy-D-ribose. Different nucleic acids can have from around 80 nucleotides (nt), as in transfer RNA (tRNA), to over 10 nucleotide-pairs in a single eukaryotic chromosome. The unit for size of nucleic acid is the base (for single-stranded species) or the base-pair (bp, for double-stranded species), with the unit Kb (thousand base-pairs) and Mb (million base-pairs). Examples of synthetic homopolynucleotides are poly(uridylate) or poly(deoxyadenylate), in poly(U) or poly(dA)... 

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