Here's why:

* ATP (Adenosine triphosphate): ATP is the primary energy currency of cells. It provides the energy needed for many cellular processes, including transcription.

* Breaking the phosphate bonds: The energy released from breaking the phosphate bonds in ATP is used to drive the formation of the phosphodiester bonds that link nucleotides together in the growing RNA molecule.

* RNA polymerase: RNA polymerase, the enzyme responsible for transcription, uses ATP to provide the energy needed to move along the DNA template and unwind the DNA double helix.

In summary: ATP provides the energy required to power the enzymatic reactions that take place during transcription, ultimately allowing for the synthesis of RNA from a DNA template.