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Watson-Crick purine:pyrimidine

Figure 69. Deidation of p-RNA backbones (in their idealized conformation) fiom colinearity left purine-pyrimidine, Watson-Crick right adenine-adenine, reverse-Hoogsteen. Figure 69. Deidation of p-RNA backbones (in their idealized conformation) fiom colinearity left purine-pyrimidine, Watson-Crick right adenine-adenine, reverse-Hoogsteen.
This is consistent with there not being enough space (20 °) for two purines to fit within the helix and too much space for two pyrimidines to get close enough to each other to form hydrogen bonds between them. These relationships are often called the rules of Watson-Crick base pairing. [Pg.1315]

The DNA double heUx illustrates the contribution of multiple forces to the structure of biomolecules. While each individual DNA strand is held together by covalent bonds, the two strands of the helix are held together exclusively by noncovalent interactions. These noncovalent interactions include hydrogen bonds between nucleotide bases (Watson-Crick base pairing) and van der Waals interactions between the stacked purine and pyrimidine bases. The hehx presents the charged phosphate groups and polar ribose sugars of... [Pg.7]

The formation of three-stranded nucleic acid complexes was first demonstrated over five decades ago [56] but the possible biological role of an extended triplex was expanded by the discovery of the H-DNA structure in natural DNA samples [57-59]. H-DNA is an intermolecular triplex that is generally of the pyrimidine-purine x pyrimidine type ( dot -Watson-Crick pairing and cross Hoogsteen base paring) and can be formed at mirror repeat sequences in supercoiled plasmids [59]. [Pg.162]

The liberation of the third, newly formed strand is of great importance in this process it is made possible by adding free dodecameric purine oligonucleotides, which can bond to the newly-formed pyrimidine matrix by Watson-Crick pairing. [Pg.157]

Figure 5-6 Outlines of the purine and pyrimidine bases of nucleic acids showing van der Waals contact surfaces and some of the possible directions in which hydrogen bonds may be formed. Large arrows indicate the hydrogen bonds present in the Watson-Crick base pairs. Smaller arrows indicate other hydrogen bonding possibilities. The directions of the green arrows are from a suitable hydrogen atom in the base toward an electron pair that serves as a hydrogen acceptor. This direction is opposite to that in the first edition of this book to reflect current usage. Figure 5-6 Outlines of the purine and pyrimidine bases of nucleic acids showing van der Waals contact surfaces and some of the possible directions in which hydrogen bonds may be formed. Large arrows indicate the hydrogen bonds present in the Watson-Crick base pairs. Smaller arrows indicate other hydrogen bonding possibilities. The directions of the green arrows are from a suitable hydrogen atom in the base toward an electron pair that serves as a hydrogen acceptor. This direction is opposite to that in the first edition of this book to reflect current usage.
C+ G C, where C+is cytosine in its N-l protonated (low pH) form. The Watson-Crick strands are antiparallel, as indicated by the and 0 signs. The third strand may have either orientation, but when it contains largely pyrimidines it is parallel to a purine-rich strand. An example is shown in Fig. 5-24. [Pg.208]

DNA polymerases have just one binding site for all four combinations of base pairing—AT, TA, GC, and CG. The specificity of these sites is dictated by the Watson-Crick pairing rules, in that the sites themselves appear to recognize just the overall shape of a correct purine-pyrimidine pair, with the precise specificity resulting from the complementary nature of the base pairing. The polymerase catalyzes the transfer of a complementary deoxynucleoside monophosphate from its triphosphate to the 3 -hydroxyl of the primer terminus (equation 14.1). [Pg.213]

Fig. 1. Elements of DNA. stricture (a) a deoxypolynucleotide chain, which reads d(ACTG) from 3 — 5 or d(GTCA) from 3 — 5 and (b) and (c) the Watson-Crick purine-pyrimidine base pairs, A-T and G-C. respectively, where—s represents aliachinenl lo the deoxyribose... Fig. 1. Elements of DNA. stricture (a) a deoxypolynucleotide chain, which reads d(ACTG) from 3 — 5 or d(GTCA) from 3 — 5 and (b) and (c) the Watson-Crick purine-pyrimidine base pairs, A-T and G-C. respectively, where—s represents aliachinenl lo the deoxyribose...
Figure 5.1 Deoxyribozyme-catalyzed RNA cleavage. (A) The cleavage reaction, which forms 2,3,-cyclic phosphate and 5-OH RNA termini. (B) Individual deoxy-ribozymes and their target sequences for efficient cleavage of all-RNA substrates. N, any nucleotide R, purine Y, pyrimidine. Outside of the expheidy indicated nucleotides, any RNA sequence is tolerated as long as Watson-Crick RNA DNA covariation is maintained. Figure 5.1 Deoxyribozyme-catalyzed RNA cleavage. (A) The cleavage reaction, which forms 2,3,-cyclic phosphate and 5-OH RNA termini. (B) Individual deoxy-ribozymes and their target sequences for efficient cleavage of all-RNA substrates. N, any nucleotide R, purine Y, pyrimidine. Outside of the expheidy indicated nucleotides, any RNA sequence is tolerated as long as Watson-Crick RNA DNA covariation is maintained.
In agreement with the chemomimetic concept as defined by Eschen-moser, the panel of enzymatic transformations for the biosynthesis of purines that we currently observe in the cell can be hypothesized to have evolved from primitive chemical processes [48-50]. 2-Carbonitrile and 2-carboxamide AICA and AICN derivatives, respectively, were also used as intermediates for the synthesis of adenine 1 and 8-substituted adenines 7 and 8 [51]. In principle, purine derivatives 7 and 8 may pair with pyrimidine bases by formation of Watson-Crick or Hoogsteen hydrogen bond interactions. [Pg.33]


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See also in sourсe #XX -- [ Pg.491 ]




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Crick

Purines, pyrimidines

Watson

Watson-Crick purine-pyrimidine base

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