Polydeoxyribonucleotide, structure

Nucleotides are the building blocks of nucleic acids their structures and biochemistry were discussed in chapter 23. When a 5 -phosphomononucleotide is joined by a phosphodiester bond to the 3 -OH group of another mononucleotide, a dinucleotide is formed. The 3 -5 -linked phosphodiester intemucleotide structure of nucleic acids was firmly established by Lord Alexander Todd in 1951. Repetition of this linkage leads to the formation of polydeoxyribonucleotides in DNA or polyribonucleotides in RNA. The structure of a short polydeoxyribonucleotide is shown in figure 25.3. The polymeric structure consists of a sugar phosphate diester backbone with bases attached as distinctive side chains to the sugars. 

Single-stranded polydeoxyribonucleotides are, as a rule, less stacked and structured than their ribo counterparts. They frequently show different titration behavior [e.g., poly(dC) forms the double helical acid form two pH units higher than poly(C) under the same experimental conditions] and optical properties. 

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