Adenine-thymine

Figure 3.10 Stniciural details of the bridging units between pairs of bases in separate strands of the double helix of DNA (a) the thymine-adenine pair (b) the cytosine-guanine pair.

The sugar component in RNA is ribose, and the sugar in DNA is 2 -deoxy-ribose. (The prefix 2 -deoxv indicates that oxygen is missing from the 2 position of ribose.) DNA contains four different amine bases, two substituted purines (adenine and guanine) and two substituted pyrimidines (cytosine and thymine). Adenine, guanine, and cytosine also occur in RNA, but thymine is replaced in RNA by a closely related pyrimidine base called uracil. 

Sulphonamides are structural analogues of PABA. They competitively inhibit the incorporation of PABA into dihydropteroic acid and there is some evidence for their incorporation into false folate analogues which inhibit subsequent metabolism. The presence of excess PABA will reverse the inhibitory action of sulphonamides, as will thymine, adenine, guanine and methionine. However, these nutrients are not normally available at the site of infections for which the sulphonamides are used. 

Florian, J. Goodman, M.F. Warshel, A., Free energy perturbation calculations of DNA destabilization by base substitutions the effect of neutral guanine-thymine, adenine-cytosine and adenine-difluorotoluene mismatches, J. Phys. Chem. B 2000,104, 10092-10099. 

Fig. 5 Structure of initial thymine-adenine ISC and its rearrangement to the isolated ISC product.

Four different cyclic amine bases occur in DNA adenine, guanine, cytosine, and thymine. Adenine, guanine, and cytosine also occur in RNA, but thymine is replaced in RNA by a related base called uracil. 

CNS- > CIO4 > Ac- > Br > Cl > HCOO-. A similar series is found on the solubility of the bases thymine, adenine etc.212. Cl3COO >CNS >C10j >J > Br have salt-in effects, SO4 Cl- show salt-out effects181 212. Salt-in effects were observed on acetyltetraglycine ethyl ester too in the series213 SCN- >... 

The DNA sugar is 2-deoxy-D-ribose. The four heterocyclic bases in DNA are cytosine, thymine, adenine, and guanine. The first two bases are pyrimidines, and the latter two are purines. In nucleosides, the bases are attached to the anomeric carbon (C-1) of the sugar as p-N-glycosides. In nucleotides, the hydroxyl group (-OH) at C-3 or C-5 of the sugar is present as a phosphate ester. 

Know the structures of cytosine, thymine, adenine, guanine, uracil, 2-deoxy-D-ribose, D-ribose. 

A number of studies on photochemistry of the nucleic acid bases in aqueous solutions demonstrated that while uracil undergoes reversible hydration under exposure to UV irradiation, the other bases (thymine, adenine, and guanine) were stable [41,42], However, the sensitivity of dissolved thymine to UV irradiation can be significantly increased if the solution is rapidly frozen [43]. In 1960 the thymine photoproduct was isolated from irradiated frozen aqueous solution of thymine. Elemental analysis, molecular weight measurements, powder X-ray diffraction, NMR and IR spectroscopy confirmed that the most likely photoproduct is a thymine dimer [20]. Similar photoproduct was obtained by hydrolysis of irradiated DNA. Its formation was attributed to reaction between two adjacent thymine groups on the same DNA chain [44], Independently an identical compound was isolated from DNA of UV-irradiated bacteria [45]. 

TRANSVERSION MUTATION A base-pair substitution mutation in which the purine pyrimidine base-pair orientation Is reversed, as in adenine thymine - thymine adenine. 

Another key difference between RNA and DNA is the presence of thymine in DNA instead of the uracil in RNA. Thymine is simply uracil with an additional methyl group. The four common bases of DNA are cytosine, thymine, adenine, and guanine. 

The complementary DNA base pair of cytosine-guanine (C-G) and thymine-adenine (T-A) forms the basis of the highly selective DNA recognition ability. 

Q2 Amino acids are needed to produce the plasma membrane Bi2 (cyanocobal-amine), which is stored in the liver, is required for synthesis of DNA. Folic acid is also needed for synthesis of DNA (it is a component of thymine, adenine and guanine) and for RNA synthesis. Other B vitamins are required for haem synthesis and oxidative metabolism. Iron is required in ferrous form for haemoglobin synthesis vitamin C helps maintain iron in its ferrous form. 

Cyclic peptide nucleotide hybrids with various ring sizes are obtained by intramolecular condensation of 3 -N-aminoacyl/peptidyl-5 nucleotides using EDCCl. A series of nor-bornene derivatives containing nucleic acid bases (thymine, adenine, guanine or uracil) are... 

---