DTTP

Two new strands form as nucleotides that are complementary to those of the original strands are joined by phosphodiester linkages The sources of the new bases are dATP dGTP dCTP and dTTP already present in the cell... 

Add reverse transcriptase and substrates dATP, dTTP, dGTP, dCTP... 

Fig. 24.4 Thymidylate synthase (TS) biochemical pathway. dUMP-deoxyuridine monophosphate, dTMP-deoxythymine monophosphate, dTTP-deoxythymine triphosphate.

In 1995, Horie et al. described a polymorphic tandem repeat found in the 5 -un-translated region of the thymidylate synthase gene [70]. Thymidylate synthase (TS TYMS) catalyzes the intracellular transfer of a methyl group to deoxyuridine-5-monophosphate (dUMP) to form deoxythymidine-5-monophosphate (dTMP), which is anabolized in cells to the triphosphate (dTTP). This pathway is the only de- novo source of thymidine, an essential precursor for DNA synthesis and repair. The methyl donor for this reaction is the folate cofactor 5,10-methylenetetrahydro-folate (CH2-THF) (Figure 24.4). 

Figure 16. Differential cross sections da/dttp for the ionization of He by 2-MeV protons as a function of the scattering angle of the proton. Experimental data are from Kristensen and Horsdal-Pedersen [7], Theoretical results are present CDW-EIS calculations.

Ribonucleotide reductase works on ribo-A, -U, -G, -C diphosphates to give the deoxynucleotide. The deoxyuridine, which is useless for RNA synthesis, is converted to deoxythymidine by the enzyme thymidylate synthase, which uses methylene tetrahydrofolate as a one-carbon donor. The odd thing here is that ribonucleotide reductase uses the UDP as a substrate to give the dUDP. This must then be hydrolyzed to the dUMP before thymidylate synthase will use it to make dTMP. Then the dTMP has to be kinased (phosphorylated) up to dTTP before DNA can be made. 

Figure 10.3. Mass array, (a) Primer binding (b) primer extension enzyme, ddATP and dCTP/ dGTP/dTTP addition (c) primer terminates (d) primer extension products ready for MALDI-MS (e) MS spectrum of primer extension products. Each addition of a nucleotide to the primer extension product increases the mass by 289 to 329 Da, depending on the nucleotide added. The mass difference is easily resolved by MALDI-TOF, which has the ability to detect differences as small as 3 Da. Printed by kind permission of Sequenom. (See color insert.)...

Thymine Deoxythymidme Deoxythymidylic acid Deoxythymidine monophosphate (dTMP) Deoxythymidine diphosphate (dTDP) Deoxythymidine triphosphate (dTTP)... 

Required substrates dATP, dGTP, dCTP, dTTP ATP, GTP, CTP, UTP j... 

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