G-C pairs

Each pair contains one purine and one pyrimidine base This makes the A T and G C pairs approximately the same size and ensures a consistent distance between the two DNA strands... 

As indicated in Chapter 11, the base pairing in DNA is very specific the purine adenine pairs with the pyrimidine thymine the purine guanine pairs with the pyrimidine cytosine. Further, the A T pair and G C pair have virtually identical dimensions (Figure 12.10). Watson and Crick realized that units of such similarity could serve as spatially invariant substructures to build a polymer whose exterior dimensions would be uniform along its length, regardless of the sequence of bases. 

The feasibility of identifying these edges of water base pairs has been supported by our studies of mitomycin C interacting with the model system for AT base pairs 29). Interactions of either component with mitomycin C are not observed but a complex is formed when all three components are present. Chemical shift changes observed in the NMR spectra support the structure 47 for the termolecular complex. The broader implication is that mitomycin C will likewise recognize the minor groove side of a G-C pair (it is known to alkylate the guanidine on this side)31 ... 

Cytosine can become deaminated spontaneously or by reaction with nitrous acid to form uracil. This leaves an improper base pair (G-U), which is eliminated by a base excision repair mechanism (Figure 1-2-5). Failure to repair the improper base pair can convert a normal G-C pair to an A-T pair. 

Native DNA undergoes reversible unwinding and separation of strands (melting) on heating or at extremes of pH DNAs rich in G C pairs have higher melting points than DNAs rich in A=T pairs. 

Since the Z form of DNA is favored in regions rich in G-C pairs,118119 it is reasonable to expect that it may... 

Is the selectivity of the individual A-T / G-C pair matching reflected in the overall selectivity of such sensors Why yes or no ... 

Figure 2.31 Watson-Crick base pairing, (a) bonds in the G-C pair makes it more stable than...

In the lower panel of Fig. 17.3 are melt curves for HPc at 1574 cm-1 (squares) and 1661 cm-1 (circles). The upper panel shows melt curves for tRNAphe at 1620 cm-1 (squares) and 1661 cm-1 (circles). For HPC (lower), these wavenumbers correspond to base stacking (1574 cm-1 ring vibrations) and base pairing (1661 cm-1 G-C pairing). The melt curves (and subsequent thermodynamics) are virtually identical. It will be shown later, however, that the kinetics at the two different wavenumbers are very different. The wavenumbers for the tRNA (upper) correspond to A-U base... 

At this point, it may be interesting to indicate that the fact that the G-C pairs constitute the unstable part of the genome and that they mutate spontaneously more frequently than the A-T pairs has been reported in a number of publications.180-182 One cannot and should not, however, conclude from this situation that miscouplings through tautomerization of bases are the principal cause of spontaneous mutations, because those are definitely known to be due to a large series of causes, the relative importance of which is difficult to ascertain. The concordance between the theoretical predictions and the experimental facts is, however, worthwhile stressing, as an eventual discordance would certainly have been by some. 

Table XX confirms, as indicated in Section I of this review, that among the natural complementary pairs, the G-C pair has a much greater interaction energy than the A-T pair. It shows also that...

Sources of deoxyuridine in DNA include the presence of dUTP because dUMP (the substrate for thymidylate synthase) or dUDP (from ribonucleotide reductase action on UDP) are phosphorylated to the triphosphate. DNA polymerase recognizes these compounds as substrates. Another source is the deamination of deoxycytidine in DNA, promoted by a variety of compounds. If deoxyuridine is on a template strand of the DNA, it will direct the incorporation of an A in the newly made strand of DNA. This will convert a G-C pair to an A-T pair. 

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