dinukleotydy

Dinukleotydy (dinucleotides) are chemical entities consisting of two nucleotides joined by a phosphodiester bond. Each nucleotide contains a sugar, a phosphate group, and a nitrogenous base (adenine, cytosine, guanine, thymine in DNA; adenine, cytosine, guanine, uracil in RNA). In DNA, dinucleotides arise from deoxyribonucleotides; in RNA from ribonucleotides. They are the simplest structural units of nucleic acids and can serve as building blocks for longer polynucleotides.

Dinucleotides are formed by a condensation reaction between the 5' phosphate of one nucleotide and the 3' hydroxyl of the adjacent nucleotide, producing a 5'-phosphate–3'-phosphodiester linkage with 5' to 3' polarity in the backbone.

Two broad contexts are relevant. First, genetic dinucleotides within DNA or RNA, such as CpG dinucleotides (cytosine followed by guanine), which are major targets of DNA methylation. Methylated CpG sites are mutation hotspots and influence genome composition. Second, dinucleotide cofactors in biochemistry, such as NAD+ and NADP+, which consist of two nucleotides linked by a phosphate bridge and function as electron carriers; flavin adenine dinucleotide (FAD) is a related dinucleotide-containing cofactor.

In summary, dinukleotydy describe two-nucleotide units in nucleic acids and related dinucleotide cofactors that play central roles in genetics, epigenetics, and metabolism.