Nucleic Acids and Pyrolysis of Oligonucleotides

Nucleic acids are biopolymers present in every living cell, with monomeric units consisting of a carbohydrate linked via a p-D-glycosidic bond to a heterocyclic base and interconnected by phosphodiester bonds at positions C-3 and C-5. The monomeric units of nucleic acids can be considered the nucleotides that are formed from a carbohydrate residue connected to the base by the p-D-glycosidic bond and to a phosphate group at C-5. The molecules derived from nucleotides by removing the phosphate group are the nucleosides. 

In deoxyribonucleic acid (DNA) the carbohydrate is 2-deoxy-D-ribose, while in ribonucleic acid (RNA) the carbohydrate residue is ribose. Three types of RNA were recognized, and they can be messenger RNA (mRNA), transfer RNA (tRNA), or ribosomal RNA (rRNA), which is the most abundant in cells. Values between 10 and 10 Dalton have been reported for the molecular weight of DNA, and the molecular weight is about 10 for rRNA, 10 for mRNA, and lOMor rRNA. The simplified structures of DNA and RNA are the following  

The heterocyclic bases present in nucleic acids are certain purines and pyrimidines. 

The bases always present in DNA are adenine, guanine, cytosine, and thymine, while in RNA the bases are adenine, guanine, cytosine, and uracil. Trace amounts of other bases are occasionally present in DNA and RNA. For example, DNA may contain 5-hydroxymethyl cytosine and several N-methyl purines. The tRNA may contain several unusual bases such as certain methyl purines or hydroxymethyl pyrimidines. 

Similarly to proteins, both DNA and RNA have a secondary and a tertiary structure. The secondary structure of DNA shows two chains running in opposite directions, coiled in a left-handed (double) helix about the same axis. All the bases are inside the helix, and the sugar phosphate backbone is on the outside (see e.g. [1]). The chains are held together by hydrogen bonds between the bases with adenine always paired with thymine and guanine paired with cytosine. The base pairing in DNA is shown below  

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