Like  DNA RNA  is  a  long  polymer  having  of  nucleotides joined by 3'5' phosphodiester  bonds. Furthermore, there are some differences:

?   The bases in RNA are adenine abbreviated A, guanine G, uracil U and cytosine C. Thus thymine in DNA is replaced through uracil in RNA, a several pyrimidine shown in the figure. Furthermore, such as thymine, uracil can form base pairs with adenine.

?   The sugar in the RNA is ribose rather than deoxyribose as in the DNA.

Equivalent ribonucleosides are guanosine, adenosine, cytidine and uridine. The corresponding   ribonucleotides   are adenosine   5'-triphosphate (ATP), guanosine 5'-triphosphate (GTP), cytidine 5'-triphosphate (CTP) and uridine 5'-triphosphate (UTP). As  with  DNA,  the  nucleotide  series  of  RNA  is  also  written  as  a  base sequence  in the 5' →  3' direction.  Thus GUCAAGCCGGAC is the sequence of one short RNA molecule.

                          Figure:   (a) Uracil, (b) ribose.