Figure 2.
Nucleotides as they would appear within a nucleic acid chain. The difference between RNA, 2′-O-methylated RNA and DNA is the nature of the group at the 2′ position of the ribose (highlighted in red). In RNA the 2′ position carries a hydroxyl. The reactivity of this group is a major determinant of RNA catalytic activity. 2′-O-Methyl RNA occurs extensively on eukaryotic and archaeal RNAs, particularly ribosomal RNA, where the reaction is snoRNA-mediated. Site-specific protein methylases catalyse the rRNA methylation in bacteria. Methylation eliminates the propensity for 2′-OH-mediated catalytic activity. In DNA, hydrogen is at the 2′ position on the ribose. Ribonucleotide reductases utilise free radical chemistry to reduce the 2′-OH of free ribonucleotides to a 2′-H, forming free deoxyribonucleotides. Bases are shown in blue: uracil in RNA and 2′-O-methyl RNA and thymine in DNA.