Thymine-cytosine base pair

Examine AT pair and GC pair, adenine-thymine and guanine-cytosine base pairs, respectively. Identify the hydrogen bonds in each. Are they the same as those you sketched Are the base pairs flat as normally drawn in textbooks, or are they significantly puckered or twisted ... 

Density of states weighted Franck-Condon factor Deoxyribonucleic acid Barrier height for the adiabatic hole motion Difference in ionization potentials of adenine-thymine and guanine-cytosine base pairs... 

Since coiled chains of proteins are known to uncurl because of ionic repulsions when ionization occurs, Reid (1957) suggested that excited state dissociation acts as a trigger in rapid biological processes. The 7-azaindole dimer, which undergoes photo-induced double proton transfer (see Section 4), has similarities to the adenine-thymine and guanine-cytosine base pairs of DNA. Its excited state proton transfers have been proposed as possible mechanisms of mutagenesis (Ingram and El-Bayoumi, 1974). 

Yet another effect of the action of Ag" has been described, namely, its interaction with nucleic acids [112]. The Ag" ion interacts preferentially with the bases found in DNA rather than with the phosphate group [113-118]. The reaction between Ag and a GC (guanine-cytosine) base pair proceeds via two steps, whereas that between Ag" and an AT (adenine-thymine) base pair requires only one step [116], Ag appears to be attached to the N atom... 

Substitution pattern of H-bonding donor and acceptor groups for adenine-thymine and guanine-cytosine base pairs in the major and minor groove... 

DNA wound around one another. The sugar-phosphate backbone is on the outside of the helix, and complementary pairs of bases extend into the center of the helix. The base pairs are held together by hydrogen bonds. Adenine base pairs with thymine, and cytosine base pairs with guanine. The two strands of DNA in the helix are antiparallel to one another. RNA is single stranded. 

Problem 21.57. At high temperatures, deoxynucleic acids become denatured, i.e., they unwind from double helices into disordered single strands. Account for the fact that the higher the content of guanine-cytosine base pairs relative to adenine-thymine base pairs, the higher the temperature required to denature a DNA double helix. 

Figure 13 (A) Gonzalez-Rodriguez s cyclic H-bonded tetramer based on guanine-cytosine base pairing and (B) the reference system (R and R are solubilizing groups). (C) An alternative base pairing system based on aminoadenine—thymine.

To account for the observed base ratios and uniform thickness of DNA, Watson and Crick postulated that purine and pyrimidine bases project inward toward the axis of the helix and always pair in a specific manner. According to scale models, the dimensions of an adenine-thymine base pair are almost identical to the dimensions of a guanine-cytosine base pair, and the length of each pair is consistent with the core thickness of a DNA strand (Figure 20.7). Thus, if the purine base in one strand is adenine, then its complement in... 

The hydrogen bonds formed between nucleic acid base pairs are crucial to the structure and function of DNA and have therefore been the subject of considerable theoretical work. - Two systems of particular interest are the Watson-Crick guanine-cytosine (GC) and adenine-thymine (AT) base pairs depicted in Figures 5 and 6. Hydrogen bond distances and strengths from high-level ab initio calculations on the GC and AT base pairs could be used to parameterize molecular mechanical force fields that then could be used to study the structure and dynamics of extended double-stranded DNA helices. 

Gorb L, Podolyan Y, Dziekonski P et al (2004) Double-proton transfer in adenine-thymine and guanine-cytosine base pairs. A post-Hartree-Fock ab initio study. J Am Chem Soc... 

Fig. 1. Hydrogen bonding betweeb adenosine/thymine Oeft) and guanosine/cytosine base pairs of DNA.

Besides the canonical triplexes formed, for example, between thymine and the adenine-thymine base pair and cytosine and the guanine-cytosine base pair other combinations have been suggested to form stable triplexes, e.g. G-TA, G-GC and T-GC [43], The stability of triplexes depends on pH, ionic strength, temperature, and, in cases where the Watson-Crick duplex is part of a plasmid DNA, it depends on supercoil density [44]. 

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