Nucleic acid hyperchromicity

Nucleic acids undergo heUx-to-coil transition with increasing temperature. The transition temperature Tm is defined as the temperature corresponding to which the hyperchromicity, H (absorbance at any temperature/absorbance at room temperature) is given by ... 

Nucleic Acid Structure Explain why the absorption of UVlight by double-stranded DNA increases (hyperchromic effect) when the DNA is denatured. 

Nucleic acids absorb UV light with an absorption maximum at approximately 260 nm. This absorption mainly results from the nucleobases. Importantly, double-stranded DNA has a lower molar absorption coefficient, e, than calculated for the sum of the molar absorption coefficients of the bases. Accordingly, duplex denaturation is accompanied by increased UV absorption [2]. This effect is termed hyperchromicity and originates from the disruption of base stacking. 

This increase in the absorption spectrum following denaturation (destruction of secondary structure) is termed the hyperchromic effect (Fig. V-9). Conversely, the decrease in the absorption spectrum on renaturation of these types of nucleic acids (restoration of secondary structure) is termed the hypochromic effect. These effects are observed in Experiment 19. 

Fixation of ais- and trons-DDP, but not [Pt(dien)Cl]Cl, disrupts DNA basestacking. Spectroscopic studies such as UV hyperchromism and circular dichroism reflect the immediate environment of the base and are sensitive probes of conformational changes involving, at most, several nucleic acid bases. Between... 

Fig. 6.11. Stability of double-stranded DNA (dsDNA) based on the GC content of the nucleic acid. The melting temperature is detected by a hyperchromic shift that occurs during the temperature-induced melting of dsDNA to single-stranded DNA and is shown to increase as the GC content of dsDNA increases.

Apparently, both the granulopoietic and the erythropoietic lineage participated in the megaloblastic proliferation. Thus, the most salient hematological feature was a hyperchromic megaloblastic anemia. The only other abnormality was found in the urine, where large amounts of pyrimidine bases, later demonstrated to be orotic acid, were excreted. Such observations suggest either a block in orotic acid use for further biosynthesis of pyrimidine and nucleic acid, or interference with renal orotic acid excretion. 

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