Nucleotides ultraviolet light absorbed

There are a number of distinct enzymes which deaminate purine and pyrimidine nucleosides and nucleotides, as well as the free bases. However deamination of purines and pyrimidines in nucleic acids takes place slowly, if at all. Ammonia and the corresponding hydroxyl analog are the products of these reactions. Deamination is known to be irreversible in some cases and can be followed by changes in ultraviolet light absorbing properties 21). 

Direct Repair Several types of damage are repaired without removing a base or nucleotide. The best-characterized example is direct photoreactivation of cyclobutane pyrimidine dimers, a reaction promoted by DNA photolyases. Pyrimidine dimers result from an ultraviolet light-induced reaction, and photolyases use energy derived from absorbed light to reverse the dam-... 

Another property of pyrimidines and purines is their strong absorbance of ultraviolet (UV) light, which is also a consequence of the aromaticity of their heterocyclic ring structures. Figure 11.8 shows characteristic absorption spectra of several of the common bases of nucleic acids—adenine, uracil, cytosine, and guanine—in their nucleotide forms AMP, UMP, CMP, and GMP (see Section 11.4). This property is particularly useful in quantitative and qualitative analysis of nucleotides and nucleic acids. 

Most HPLC instruments monitor sample elution via ultraviolet (UV) light absorption, so the technique is most useful for molecules that absorb UV. Pure amino acids generally do not absorb UV therefore, they normally must be chemically derivatized (structurally altered) before HPLC analysis is possible. The need to derivatize increases the complexity of the methods. Examples of derivatizing agents include o-phthaldehyde, dansyl chloride, and phenylisothiocyanate. Peptides, proteins, amino acids cleaved from polypeptide chains, nucleotides, and nucleic acid fragments all absorb UV, so derivatization is not required for these molecules. 

Nucleotides absorb light strongly in the near-ultraviolet region of the spectrum. This makes it possible to use spectrophotometry to quantitate DNA and RNA (Figure 4,5). 

The detection of DNA can be performed by ultraviolet (UV) detection. However, this has poor sensitivity and subject to much interference. The addition of special dyes such as YO-PROl, BODIPY, and thiazole orange to the separation buffer in CE enables the use of laser-induced fluorescence (LIE), which improves the detection by a factor of 100 times. LIE eliminates the interferences from the nucleotides in the reaction mixture, which absorb light in the UV region. Also, because the sample is diluted, matrix effects become negligible. This enables introducing the sample by eiectrokinetic injection with stacking (concentration on the capillary) too. 

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