Nucleic acid base composition

It is more difficult to conceive how the nucleic acid bases such as adenosine may be achieved in prebiotic syntheses. However, adenine, C5H5N5, corresponds in composition to a pentamer of hydrogen cyanide and could result by way of a trimer of HCN, 20, and the adduct of ammonia with HCN, 21 ... 

The popular interpretation of these results in terms of the origin of life shows how much this question is still on the researcher s mind. There are now questions about the composition of Stanley Miller s primordial soup, but lipidlike organic molecules, amino acids, and nucleic acid bases have been found in meteors, which means they exist extraterrestrially, which means that the stuff of life is out there, somewhere else. ... 

Figure 10.7 Electrophoretogram of dendritic nucleic acid 4 (lane 2) and a linear analog of identical base composition (lane 3). Lanes 1 and 4 marker dyes xylene cyanol (XC) and bromophenol blue (BPB). (Reprinted with permission from reference 23, copyright (1993) American Chemical Society.)...

In ion-exchange chromatography nucleic acids are separated on the basis of the difference in charge. Each nucleic acid has a different net charge based on the number of phosphate groups in the molecule (base length) and the respective charges on the bases (base composition). The latter effect is relatively minor and so separation depends almost exclusively on size. Separation... 

A plot of the optical absorbance at 260 nm (the wavelength of maximum light absorption by nucleic acids) versus temperature is known as a melting curve (Fig. 5-45). The absorbance is lower, by up to 40%, for native than for denatured nucleic acids. This hypochromic effect (Chapter 23) is a result of the interaction between the closely stacked bases in the helices of the native molecules. The melting temperature Tm is taken as the midpoint of the increase in absorbance (Fig. 5-45). As the percentage of G + C increases, the nucleic acid becomes more stable toward denaturation because of the three hydrogen bonds in each GC pair. Tm increases almost linearly with increases in the G + C content. In the "standard" citrate buffer (0.15 M NaCl + 0.015 M sodium citrate, pH 7.0) Eq. 5-22 holds. The exact numerical relationship depends strongly upon the ionic composition and pH of the medium.37 72 552 553... 

The following molecules are bases that are part of the nucleic acids involved in the genetic code. Identify the hybridizations of all the atoms except the hydrogens, the composition of the bonds, and the orbitals occupied by lone pairs. Each unlabeled angle represents a C atom. 

Purine bases IC. Computer programs for calculating the relative compositions of nucleotides, nucleic acids, purines. 

Usually the asymmetric unit of a helical polynucleotide chain is effectively one nucleotide residue. To date, over two dozen nucleic acid structures of this kind—both native and synthetic and of varying base composition and sequence have been defined accurately and in most cases refined extensively. 

---