Complex sentence: Nucleotides serve to carry packets of energy within the cell in the form of the nucleoside triphosphates (ATP, GTP, CTP and UTP), a central role in metabolism.
Split into simpler sentences: Nucleotides serve to carry packets of energy within the cell (ATP). In the form of the nucleoside triphosphates (ATP, GTP, CTP and UTP), nucleotides play central roles in metabolism.