Nucleic acid strands, components

The unique properties of oligonucleotides create crosslinking options that are far different from any other biological molecule. Nucleic acids are the only major class of macromolecule that can be specifically duplicated in vitro by enzymatic means. The addition of modified nucleoside triphosphates to an existing DNA strand by the action of polymerases or transferases allows addition of spacer arms or detection components at random or discrete sites along the chain. Alternatively, chemical methods that modify nucleotides at selected functional groups can be used to produce spacer arm derivatives or activated intermediates for subsequent coupling to other molecules. 

The genetic information of eukaryotic cells is propagated in the form of chromosomal DNA. Besides the nucleic acid component, chromosomes contain architectural proteins as stoichiometric components, which are involved in the protective compaction of the fragile DNA double strands. Together, the DNA and proteins form a nucleoprotein structure called chromatin. The fundamental repeating unit of chromatin is the nucleosome core particle. It consists of about 147 base pairs of DNA wrapped around a histone octamer of a (H3/H4)2 tetramer and two (H2A-H2B) heterodimers. One molecule of the linker histone HI (or H5) binds the linker DNA region between two nucleosome core particles (Bates and Thomas 1981). 

Catterall H, Davies MJ, Gilbert BC (1992) An EPR study of the transfer of radical-induced damage from the base to sugar in nucleic acid components relevance to the occurrence of strand-breakage. J Chem Soc Perkin Trans 2 1379-1385... 

Once the early code reader had been produced from RNA, which is the active component even in modern ribosomes, the potential information stored in the nucleic acid chains became defined and accessible and the protein products could be recruited as expeditors of the expression of a limitless reservoir of information. The reiteration of complementary strands of nucleic acids never stopped even when all possibilities of every possible protein plus all the failures were produced many times. All structural motifs were exhausted and all of them were potentially available to nascent cells they just had to be there to be collected in a grab-bag fashion. How much nucleic acid material was there Was it enough to buy all the tickets in the lottery ... 

Nucleic acids can form complex structures that consist of more than two strands. Recently, the interest in structures and functions of the DNA bases polyads has significantly increased. It has been shown that guanine tetrads are vital components of many biologically important processes. 

A time sequenced, homogeneous transfer of molecular information to new nucleic acid components giving rise to self replication in the form of two new daughter strands. This leads to extramolecular proliferation (transfer of information to successive generations). 

Three levels of protein-nucleic acid recognition have been observed. Nature provides three examples of protein-nucleic acid interactions which we shall consider. The nucleic acid component can be (1) a single nucleotide, e.g., a coenzyme or a substrate, (2) a single-stranded DNA or RNA as in ribonucleases A and T, or (3) a double-stranded DNA or RNA as in the highly specific complexes with repressors in the tRNA-synthetase complex, or in the unspecific nuclease DNase I. 

The damages caused by ionizing radiations in nucleic acid and their components are obviously detrimental to the passage of genetic information that requires specific order of intact purine and pyrimidine bases in the DNA strands. Alterations in these bases and the DNA molecules in general can lead to mutations and lethal genes. The disruption of RNA molecules interferes with protein synthesis and can result in eventual cell death. 

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