1- thymine, biological activity

PES has been applied to study biologically active molecules with amino groups and their constituents like nucleic bases and related compounds (e.g. adenine, guanine, thymine, cytosine, hypoxanthine and their methyl derivatives)113-120 and amino acids92,121,122 or their methyl esters123. 

In addition to the protein and low-molecular-weight thiols that react with PAN, there are several other reactive biochemicals. Reduced nicotinamide derivatives are susceptible to oxidation by PAN (at 72 ppm for 1-5 min), whereas the oxidized forms are resistant. The capability of PAN to oxidize these compounds rapidly dissipates in aqueous solution, with a half-life of 4-10 min, depending on pH. The oxidation products appear to be the biologically active forms of the nicotinamide derivatives. Purines and pyrimidines react with PAN (at 1,000 ppm for 30-120 min). The order of sensitivity is thymine, guanine, uracil, cytosine, and adenine. Their reactions were studied at relatively low pH and at high PAN concentration and are probably not of biologic significance. 

A particular dimer of thymine was the first heat-stable photoproduct isolated from photolysis of nucleic acid derivatives, and still appears to be the principal isolable product from photolysis of most examples of biologically active DNA.8,10 Investigation of this product has drawn much attention in recent years. Most of this work has been carried out on polynucleotides and nucleic acids and will be dealt with in those sections. The remaining work has been largely carried out with... 

In human tumors, the pattern of p53 mutations is dominated by base transitions (C to T or G to A) at CpG dinucleotides (23% of all mutations). Although this type of mutation has been observed at 35 different codons, 90% of human CpG transitions are at one of six hotspot codons 175,213,245, 248, 273 and 282 (Fig. 3A) known to be important in maintaining p53 biological activity. CpG dinucleotides are sites of cytosine methylation, and deamination of 5-methylcytosine producing thymine is the most characteristic event generating spontaneous mutations in mammalian cells (Barker et... 

Both analogues can sm e to iUustrate an important problem frequently associated with design of new biologically active nucleoside analogues, namely, base selectivity. Thus, the antiviral effect of acyclovir (la), a guanine derivative, is unique. The corresponding adenine analogue (Ic), which is historically the first compound of this series, is much less effective. The thymine and cytosine derivatives lb. Id have virtually no antiviral activity. ... 

The chemistry, metabolism, and clinical importance of folic acid have been the subject of many excellent reviews (A7, Gil, H14, H20, Rl). Folic acid deficiency leads to a macrocytic anemia and leucopenia. These symptoms are due to inadequate synthesis of nucleic acid. The synthesis of purine bases and of thymine, required for nucleic acid synthesis, is impaired in folic acid deficiency. Detection of folic acid activity in biologic fluids and tissues is of the utmost importance it distinguishes between the various anemias, e.g., those due to vitamin Bi2 or folic acid deficiency. Because morphology of the abnormal red cell does not help in diagnosing vitamin deficiency, one must rely on assay methods for differential diagnosis. Treatment of pernicious anemia with folic acid has led to subacute combined degeneration of the spinal cord despite... 

Make a model of a DNA molecule. (Usually biology classrooms have model kits available for this purpose.) A DNA molecule has three components a nitrogen-containing base combinations of cytosine, adenine, thymine and guanine, and ribose (a five-carbon sugar) and a phosphate group. What is the shape of this molecule How is the activity of the DNA molecule explained by its shape ... 

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