sentences:  Because nucleoside triphosphates (NTPs) need to attach to the OH- molecule on the 3' end of the RNA, transcription always occurs in the 5' to 3' direction.The four NTPs are adenosine-5'-triphosphate (ATP), guanoside-5'-triphosphate (GTP), uridine-5'-triphosphate (UTP), and cytidine-5'-triphosphate (CTP).The attachment of NTPs onto the 3' end of the RNA transcript provides the energy required for this synthesis.