Well, the energy comes from using ATP molecules. So it turns out that to actually form a peptide bond, we have to use ATP molecules as a result of the fact that the reactants are thermodynamically more stable than our products. So once again, notice that the four reaction which is a dehydrolysis reaction, is thermodynamically unfavorable. And this means that to form a peptide bond we actually have to input a certain amount of energy and that energy comes from the ATP molecules found inside our body. Now the next question is if these products are higher in energy than these reactants here, why exactly do these bonds not spontaneously break inside our body? So why don't the bonds inside the protein holding our amino acids actually break spontaneously?