Pyrimidine bases thymine

Nucleotide A subunit of DNA or RNA consisting of a purine (adenine and guanine) or a pyrimidine base [thymine (DNA only), uracil (RNA only) and cytosine], a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). 

The tautomerisation of the purine bases adenine and guanine and of the pyrimidine bases thymine, cytosine, and uracil has important implications in molecular biology, and the occurrence of rare tautomeric forms of these bases has been suggested as a possible cause of spontaneous mutagenesis (Lowdin, 1965 Pullman and Pullman, 1971 Kwiatowski and Pullman, 1975). Three of the most likely tautomers for cytosine are shown in [87]—[89], together with the less likely imino forms [90] and [91] (Scanlan and Hillier,... 

In the early attempts to identify the nitrogenous bases of desoxy-ribosenucleic acid, some confusion arose for two reasons. At first, the products obtained by hydrolysis of nucleoprotein were studied, and there was no assurance that any particular base came from the nucleic acid rather than from the protein. Then, when the nucleic acid itself became available, the hydrolytic agents at first employed were sufficiently drastic to cause some deamination of the amino-purines (with the production of some xanthine and hypoxanthine) and some demethylation of thymine to uracil. In 1874, Piccard isolated guanine (and h3T>oxanthine) from sperm nuclein. Kossel and Neumann discovered in the hydrolysate of thymus nucleic acid two new pyrimidine bases which they named thy-mine and cytosine but they assigned incorrect empirical formulas to them. In 1894, they correctly described thymine as CsHgOjNs, but cytosine was not purified and characterized till much later. " " Levene now analyzed a series of nucleic acids from a variety of sources and found " that they all contained guanine and adenine. By mild hydrolysis of thymus nucleic acid, Steudel obtained guanine and adenine as the sole purine bases and demonstrated that they occur in equi-molecular proportions. Levene and Mandel confirmed this result and showed that the two purine bases and the two pyrimidine bases (thymine and cytosine) all occur in thymus nucleic acid in equimolecular proportions. 

This figure, by Oliveira Brett and Matysik [80], showed for the first time that the pyrimidine bases thymine and csdosine can imdergo oxidation on glassy carbon electrodes albeit for very positive potentials and that the... 

The photophysical behaviour of a series of methylated angelicins has been recorded using flash photochemical techniques. Irradiation of the complex formed between 4,6-dimethyltetrahydrobenzoangelicin and DNA results in the formation of cycloadducts. These arise by addition between the pyrimidine bases, thymine and cytosine and the furan ring of the angelicin. 

The genetic code incorporated in the DNA molecule consists of pairs of bases arranged in triplets. The bases utilized are the purine bases adenine (A) and guanine (G), and the pyrimidine bases, thymine (T) and cytosine (C). The basic mechanism of the... 

The pyrimidine base thymine (C5H6N2O2, also known as 5-methyluracil) has a solubility in water of 4.0 g/kg (pH = 7) at 25°C and its p/fsoH is 9.9 (there is a further dissociation afhigher pH that we will neglect here). Estimate the solubility of thymine in aqueous solutions over the pH range of 1 to 13. 

RNA polymerase moves along the DNA molecule from the 3 end of the operon to the 5 end, copying only one strand. (Copying the complementary strand wonld resnlt in nseless or harmful nonsense mRNA.) DNA and RNA are similar in composition, but DNA contains deoxyribose instead of ribose and the pyrimidine base thymine instead of uracil. The newly formed RNA is complementary to the DNA code adenine bases on one strand pair with thymine or nracil on the other strand, and guanine bases... 

Many natural products are derived from pyrimidine. The pyrimidine bases thymine, cytosine and uracil (22-24) are important as building-blocks for the nucleic acids. 5-Methylcytosine (obtained from hydrolytic extracts of tubercle bacilli) and 5-(hydroxymethyl)cytosine (obtained from the bacteriophage of Escherichia coli) are rarer. 

The pyrimidine bases thymine (T) and cytosine (C) form dimers at sites with adjacent pyrimidine moieties, so-called dipyrimidine sites, in the DNA chain, which have been well characterized with respect to chemical structure and mutagenic potential. The dimerization presented in Scheme 8.1 is a [In+ln] cycloaddition (see Section 7.3) involving the two C(5)=C(6) double bonds, leading to cyclobutane structures denoted by the symbol T< >T, or generally Pyr< >Pyr. 

Direct absorption of UV-B radiation by cellular DNA results in two major classes of lesion, both affecting the pyrimidine bases thymine (T, 46) and cytosine (C, 51) (Scheme 1.12) [22]. 

Pyrimidine base, thymine 5 present in DNA, on exposure to UV light undergoes dimerization to give 6 and 7 by [2+2]-cycloaddition reaction [8]. 

Let us stress again those building blocks with respect to which DNA and RNA differ DNA contains the pyrimidine base thymine in place of which RNA contains the pyrimidine base uracil. The pentose sugar of DNA is 2-deoxyribose, that of RNA is ribose. 

Deoxyribonucleic acid DNA the most important of the nucleic acids, occurs in mitochondria and chloroplasts, but most of it is in the nucleus. It is the carrier of all the cell s genetic information, the appropriate portion of which is placed in service instantly to meet changing circumstances in the cell. The information stored in DNA is encoded by the nature and order of the pyrimidine bases, thymine 4.1b) and cytosine (4.2), and the purine bases adenine 4.3) and guanine (4.4). Each strand of DNA has a deoxyribose-phosphoric acid backbone to which these bases are attached. Usually DNA has two such strands woimd around one another in a double helix and held together by H-bonds between each opposing pair of bases (Watson and Crick, 1953 for bond lengths and angles, see Donohue, 1968). 

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