And that's exactly what we mean by our reactants being thermodynamically more stable than our products. Now, what exactly does that actually mean about our reaction? Well, what it means is for this reaction to actually take place and for us to go from a lower energy level to a higher energy level. So for us to go from this energy level right over here to this energy level, let's say right over here, we have the input a certain amount of energy. So that means that the peptide bond formation is a process that requires energy. Now where does that energy come from in our body?