The energy for polymerization of nucleotides during transcription is supplied by the hydrolysis of phosphoanhydride bonds in nucleoside triphosphates (NTPs).

Here's how it works:

1. NTPs (like ATP, GTP, CTP, and UTP) are the building blocks for RNA.

2. Each NTP contains three phosphate groups linked together by phosphoanhydride bonds.

3. When an NTP is added to the growing RNA chain, two of the phosphate groups are cleaved off, releasing pyrophosphate (PPi).

4. This hydrolysis of the phosphoanhydride bonds is energetically favorable, meaning it releases energy.

5. This released energy is then used to drive the formation of the phosphodiester bond between the incoming nucleotide and the growing RNA chain.

So, in essence, the energy for polymerization comes from the breaking of high-energy bonds in the NTPs, not directly from the reaction itself. This process is similar to how ATP provides energy for many other cellular processes.