An RNA molecule is a chain of nucleotides with two distinct ends, called 5' ("five-prime") and 3' ("three-prime"). By convention, an RNA sequence is written and numbered in the 5' to 3' direction.


Nucleotides joined by bonds between sugar and phosphate groups. Two distinct positions on the sugar ring are bound to phophate - the 5' and 3' positions.

RNA is customarily numbered and written in the same direction as it is synthesized by all life forms.