Thymonucleic acid

Thymus-driise, /. thymus gland, -nuclein-saure, /. thymonucleic acid, thymus nucleic acid. 

This formulation is confirmed by the fact that, on deamination, " it retains its tetranucleotide structure and pentabasicity, and hence contains no phosphoamide links. Bredereck and collaborators completely methylated thymonucleic acid, obtaining a product possessing seven A -methyl and three methoxyl groups to each four phosphorus atoms. On stepwise hydrolysis, this material gave 1,6-dimethyladenine, 1,6-di-methylcytosine, and 1-methylthymine. This confirms the previously-mentioned conclusion, that the sugar is attached to position 9 of the adenine and to position 3 of the pyrimidines. 

In the case of DNA, a D-2-deoxyribose molecule is combined to each of the bases to form a nucleoside, and the nucleosides are then combined with each other with a phosphoric acid to form a polymer (DNA). On the other hand, in the case of RNA, D-ribose, instead of D-2-deoxyribose, is combined to each of the bases to form a nucleoside, and as in the case of DNA, these nucleosides are combined with each other to form a polymer (RNA). Among the bases within DNA and RNA, adenine and guanine have been described in the preceding section. In this section, cytosine, thymine, and uracil, which are pyrimidine bases, will be described. Purine derivatives exist as a constituent unit of nucleic acids and as many kinds of monomers, and these are also present in natural products, such as caffeine, inosinic acid, and cytokinin. On the other hand, as natural products, pyrimidine derivatives are rather rare. Nucleosides composed of pyrimidine bases cytosine, thymine, and uracil coupled with D-ribose are known as cytidine, thymidine, and uridine, respectively. Among these alkaloids, cytidine was first isolated from the nucleic acid of yeast [1,2], and thymidine was isolated from thymonucleic acid [3,4]. In the meantime, uridine was obtained by the weak alkali hydrolysis [5] of the nucleic acids originating from yeast. 

Thymine, T or Thy, 2,6-dlhydroxy-S-methylpyri-midtne, S-methyiuradi a pyrimidine base present in DNA. M, 126.1, m.p. 321-326°C (d,). T. was first isolated in 1893 from thymonucleic acid. For the biosynthesis of T, see Pyrimidine biosynthesis. 

Thymonucleic acid, thymus nucieic add nucleic acid from the thymus gland, effectively an obsolete term for DNA... 

The nucleic acids were discovered by Miescher in 1868-1869, when he isolated from pus cell nuclei a material which contained phosphorus, was soluble in alkali, but precipitated under acidic conditions. This material was subsequently prepared from other sources and when freed from protein it was called nucleic acid, a term introduced by Altman in 1889. The classical preparations of nucleic acid from yeast yielded a product which we now recognize as ribonucleic acid (RNA). The nucleic acid prepared from thymus glands, thymonucleic acid, was also extensively studied this material [which, in present terms, was deoxyribonucleic acid (DNA)) was different from yeast nucleic acid. From hydrolysates of these preparations the heterocyclic bases were isolated and characterized. At one time, yeast and thymus nucleic acids were thought to be representative of plant and animal nucleic acids, respectively (3). By 1909, it was apparent that yeast nucleic acid contained adenine, guanine, cytosine, uracil, phosphoric acid, and a sugar which Levene showed at that time to be D-ribose. Thymonucleic acid yielded adenine, guanine, cytosine, thymine, phosphoric acid, and a sugar which was not identified correctly until 1929, when it was characterized as 2-deoxy-D-ribose. 

The lability of the sugar component of thymonucleic acid had frustrated attempts to isolate structural subunits by chemical hydrolysis however, in 1929 a gentle hydrolytic procedure using dog intestinal enzymes yielded the expected four nucleosides, and the sugar was then characterized as 2-deoxy-D-ribose. Thus, it was evident that both types of nucleic acid were polymers of nucleotides. After recognition of DNA in plant tissues and the demonstration of RNA in animal tissues, it was apparent that cells in general contained both types of nucleic acid. 

In earlier investigations of turnover of nucleic acid, acid-soluble and phosphatide components of tissue were extracted with trichloroacetic acid and with ethei -alcohol, and the activity of the residual part was determined. Such residues contain, beside thymonucleic apid, ribonucleic acid and possibly also phosphoproteins. Since the rate of renewal of ribonucleic acid is much larger than that of thymonucleic acid, no conclusion about the value for thymonucleic acid can be drawn from these experiments. 

Franklin, R.E., Gosling, R.G. Molecular stmcture of nucleic acids. Molecular configuration in sodium thymonucleate. Nature 171 740-741, 1953. 

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