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Ribonucleoside numbering of adenine, guanine, cytosine, uracil bases and numbering of the ribose sugar for adenosine (A), guanosine (G), cytidine (C), and uridine (U). Carbon atoms are in gray, oxygen atoms are in red, and nitrogen atoms are in blue. Single lines between atoms depict single bonds, double lines between atoms depict double bonds, and hydrogens are not depicted for simplicity
