And we'll talk much more about what these are in a future electra. So basically, different functional groups have different capabilities and different reactivities. And the arrangement and sequence of these amino acids and their functional groups helps determine the ways in which the proteins are actually involved in helping the different types of reactions that exist inside our body. And this is particularly important when we'll talk about enzymes, those biological catalysts, because these biological catalysts essentially use these functional groups to carry out different types of reactions in which they speed up the biochemical processes inside our body. Now, different proteins have different characteristics. Some proteins are very, very rigid, while other proteins are not so rigid.