Watson and Crick proposed that DNA is made up of two strands that are twisted around each other to form a right-handed helix. Thus, adenine and thymine are complementary base pairs, and cytosine and guanine are also complementary base pairs.
The base pairs are stabilized by hydrogen bonds: adenine and thymine form two hydrogen bonds and cytosine and guanine form three hydrogen bonds. The sugar and phosphate of the nucleotides form the backbone of the structure, whereas the nitrogenous bases are stacked inside, like the rungs of a ladder. Each base pair is separated from the next base pair by a distance of 0.
Therefore, 10 base pairs are present per turn of the helix. The diameter of the DNA double-helix is 2 nm, and it is uniform throughout. Only the pairing between a purine and pyrimidine and the antiparallel orientation of the two DNA strands can explain the uniform diameter. The twisting of the two strands around each other results in the formation of uniformly spaced major and minor grooves Figure 3.
Figure 3. DNA has a a double helix structure and b phosphodiester bonds. Figure 5. Conclusion Ring-expanded heterocycles, nucleosides, and nucleotides possess excellent promise as broad-spectrum therapeutics against both cancers and viruses. Acknowledgments This article is dedicated to Dr. Nucleosides, Nucleotides Nucleic Acids. Trends Cardiovasc. Antiviral Res. Hilversum, Neth. Sharjah, United Arab Emirates. Drugs Aging. J Hepatol.
Linchuang Neike Zazhi. Methods Mol. Totowa, NJ, U. Org Biomol Chem. Semin Hematol. Youji Huaxue. Cambridge, MA, U. Cancer Hoboken, NJ, U. Cancer Ther. Drug Metab. Insect Physiol. Oxford, U. Acta Physiol. Tokyo , Ser. Cancer Inst. Nauk SSSR. Immunol Commun. Nucleic Acids Res.
Cancer Chemother. Nucleosides Nucleotides. Tetrahedron Lett. Biochemical and Biophysical Research Communications. Perkin Trans. Anticancer Res. Tetrahedron Letters. Breast Cancer. Agents Chemother. Cancer Invest. Qingdao Huagong Xueyuan Xuebao. Structure London. In: Modified Nucleosides: Synthesis and Applications. Loakes D. Research Signpost; Trivandrum, India: In: 5th Edition. Seidel A. Kirk-Othmer Encyclopedia of Chemical Technology.
New Approaches in Nutrition and Cancer. Nucleotides and amino acids. Synthesis and catabolism of purine. Purine Analogs and Related Heterocycles. In: Ts'o P. Academic Press; New York: Basic Principles in Nucleic Acid Chemistry. In: Chemistry and Biology of Nucleosides and Nucleotides. Harmon R. Purines include adenine and guanine whereas pyrimidines include cytosine , thymine , and uracil.
These five nitrogenous bases are regarded as primary or canonical since they are the fundamental units of the genetic code. The thymine differs from uracil in having a methyl group, which the uracil lacks.
Purine is a heterocyclic aromatic organic compound with a chemical formula of C 5 H 4 N 4. Its chemical structure is comprised of a pyrimidine ring with an imidazole ring fused to it, thus, has two carbon rings and a total of four nitrogen atoms. The pyrimidine ring of purines contains two nitrogen atoms that are located at positions 1 and 3 of the ring similar to those of pyrimidine s.
The imidazole ring attached to the pyrimidine ring has two nitrogen atoms that are located at positions 7 and 9. The molar mass of purine is Adenine can be distinguished from guanine by its amine group at position 6 and the presence of an additional double bond between N-1 and C-6 in its heterocyclic aromatic pyrimidine ring. Purines are present in all cells. In general, purines and pyrimidines occur in the same amounts inside the cell.
Purines that are manufactured biologically are referred to as endogenous purines. Apart from biosynthesis, purines may also be obtained from dietary sources, and in such case are referred to as exogenous purines. Meat and meat products, especially internal organs, are high in purines.
Anchovies, mackerel, scallops, and sardines have high-purine content. Red meat, pork, beef, poultry, and other seafood have relatively moderate amounts of purines.
Some of the plant-based purine source includes mushrooms, spinach, asparagus, cauliflower, beans, lentils, and wheat bran. Purines are ubiquitous in nature. They are produced inside the cell. In humans, purines are biosynthesized mainly in the liver.
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