Basic Cell Biology
Kedar N. Prasad in Handbook of RADIOBIOLOGY, 2020
DNA is a long chain of nucleotides and therefore is referred to as a polynucleotide. Each nucleotide is composed of three compounds linked together: (1) phosphoric acid; (2) a sugar, in the form of deoxyribose; and (3) a base (Figure 2.7). Bases are divided into two classes, purine and pyrimidine. In DNA, purines are adenine (A) and guanine (G), and pyrimidines are cytosine (C) and thymine (T). Thymine is very specific for DNA structure; therefore, 3H-thymidine has been used extensively in the study of DNA synthesis. In 1953, Watson and Crick proposed a double-helix structure for DNA in which two bases are joined together by hydrogen bonds.43 A diagrammatic structure of DNA is shown in Figure 2.8. It should be noted that adenine pairs with thymine, whereas cytosine pairs with guanine. Figure 2.9 shows a schematic representation of DNA replication. During replication of each strand, the newly formed strand attaches with the proper base of the old one to form a double-stranded DNA. A new DNA strand was synthesized in vitro by using a specific enzyme polynucleotide pyrophosphorylase, precursor of DNA, and DNA from other sources. The newly formed DNA was identical to DNA that was added to the reaction mixture. This showed conclusively that DNA acts as a template for the synthesis of another strand of DNA.
The Thymus and Immunotherapy, Reconstructive Vs. Stimulatory or Suppressive Conceptions
Marek P. Dabrowski, Barbara K. Dabrowska-Bernstein in Immunoregulatory Role of Thymus, 2019
By the action of an enzyme, polynucleotide phosphorylase, on the synthetic mononucleotide diphosphates, nucleotide polymers can be obtained. These polymers, when composed of opposite base pairs and mixed, form spontaneously double stranded complexes which demonstrate immunomodulatory properties.190,195 Two of them, namely polyinosinic/polycytidilic acid (Poly I-Poly C), and polyadenylic/polyuridilic acid (Poly A-Poly U) have been most thoroughly studied in animals and in man. Briefly, their effects depend upon the time of administration in relation to antigen injection. If injected together with antigen these helical compounds elevate antibody response, but when administered 1 to 2 d prior to antigen injection, the suppression of immune response is observed. The final effects of synthetic polynucleotides are due to their ability to stimulate sequentially T helper and T suppressor cell function, and to induce IFN production.190
The Molecular Model and DNA Double Strand Breaks
K. H. Chadwick in Understanding Radiation Biology, 2019
The DNA molecule has a well-defined three-dimensional structure originally determined by Watson and Crick in 1953 (Watson and Crick 1953). Two long polymer chains of alternating sugar and phosphate units are wound around each other in the form of a double helix. The two sugar-phosphate polymer chains are linked at each sugar unit by one of two purine–pyrimidine pairs of nucleotide bases, adenine–thymine pairs (A–T) and guanine–cytosine pairs (G–C), and, because the dimension of the A–T pair is the same as the dimension of the G–C pair, the two sugar-phosphate chains are held parallel to each other, separated by 1.2 nm, so that the structure resembles a long, twisted, lightly coiled, rope ladder on a molecular scale. The two sugar-phosphate strands are wound round each other to make one full turn every 3.4 nm in a right-handed spiral, which in turn is wound around a central axis so that a major groove and a minor groove are formed. Each complete unit of base plus sugar plus phosphate is called a nucleotide so that each strand of the DNA is a polynucleotide chain. The nucleotide purine–pyrimidine pairing occurs every 0.34 nm along the sugar-phosphate chain so that there are ten links holding the chain together for every full turn of the spiral. The sequence of the purine (A, G) and pyrimidine (C, T) bases along the chain forms the basis of the genetic code. The result, illustrated in Figure 1.1, is a very long, thin molecule reaching up to 50 mm in length with a diameter of 2 nm.
Synthesis, anti-bacterial and anti-protozoal activities of amidinobenzimidazole derivatives and their interactions with DNA and RNA
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2018
Andrea Bistrović, Luka Krstulović, Ivana Stolić, Domagoj Drenjančević, Jasminka Talapko, Martin C. Taylor, John M. Kelly, Miroslav Bajić, Silvana Raić-Malić
ICD spectra of 8b and 9b, in the presence of polyA-polyU, showed an intense increase of signal above r = 0.3, while ICD spectra of 7b with polyC-polyG showed a weaker intercalation signal above r = 0.5. This is in agreement with the results obtained by UV–Vis and thermal melting methods. Minimal changes of the intensity of the CD bands of polyC-polyG upon titration with compounds 7a, 8a–8e, and 9d, suggest a non-specific binding mode. Most probably compounds bind on the outside of the polyC-polyG polynucleotide. The intensity of negative ICD bands in polyA-polyU ICD spectra was also observed to be more intense than those in polyC-polyG spectra obtained with the same compound.
Related Knowledge Centers
- Biopolymer
- DNA
- Genome
- Molecular Biology
- Monomer
- Nucleotide
- Polymerase Chain Reaction
- Rna
- Experiment
- Nucleic Acid Double Helix