Polynucleotides stabilized forms

RNA molecules form secondary structure by folding their polynucleotide chains via hydrogen bond formations between AU pairs and GC pairs. The thermochemical stability of forming such hydrogen bonds provides useful criterion for deducing the cloverleaf secondary structure of tRNAs that is, tRNA molecules are folded into DFI... 

In addition to the reaction of mercaptopropionic acid, mixed anhydrides were also formed and identified starting from leucine and phenylalanine in the presence of Ca2+ ions, showing that RNAs can replace protein aminoa-cyl fRNA synthetase catalysts for amino acid activation. The formation of a detectable amount of aminoacyl S -phosphalc polynucleotide seems to be in contradiction with the instability predicted for aminoacyl adenylates (Table 1), however it can be explained by the low pH value increasing their stability and the fact that the selected RNA structures are likely to stabilize the mixed anhydride moiety of the covalent conjugate by favorable intramolecular interactions induced by folding. 

The inhibitions described above occurred only when the analog and polynucleotide contained complementary bases. These combinations are not the only ones in which the interaction can occur, e.g., affinity methods detect some interaction between the non-complementary poly-9-vinyladenine and polyadenylate Apparently, such complexes are too unstable to affect the enzymatic reactions nevertheless, extensive modification of the analog can increase the stability of the polymer-polynucleotide complex to the point where such a polymer can effectively inhibit the reaction. Thus, omisssion of the amino group from poly-9-vinyladenine leads to poly-9-vinylpurine and the latter polymer inhibits the reverse transcription of polyadenylate and polyuridylate The introduction of a dimethylamino group in place of the amino group of poly-9-vinyladenine abolMies all of its inhibitory effects All these effects can be correlated with the ability of polymers to form complexes with templates. 

The second model evaluation of folding patterns is based on the thermodynamic stability of polynucleotide conformations. Here, not only does this stability decide which of the many possible structures is formed (as in the preceding) but it also determines the fitness. The more stable is the optimal folding pattern for a particular sequence, the higher is its selective value ... 

The W-C DNA structure is a right-handed helix as one looks down either axis of the molecule and the helix rotates in a clockwise direction. This conformation of DNA is called B-DNA and is the form found in solution and inside cells. The double helix is stabilized by a number of forces, including hydrophobic interactions and van der Waals forces, which also help stabilize single polynucleotide chains. Collectively, these two forces are known as stacking interactions because of their contribution to the stacked arrangement of the bases in DNA. 

Before examining the conformation and stability of the platinum-DNA complex formed in vitro it is worth briefly considering the mechanism of the reaction between Pt(II) chloroammines and DNA, Cis-[Pt(NH3)2Cl2] does not react with DNA but the equated forms, [Pt(NH3)2(H20)Cl]+ and [Pt(NH3)2(H20)2]2+, bind covalently to the polynucleotide (20) and the overall reaction liberates 2 Cl" (21). 

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