And that's because what this does is it tells our cells not to break down and degrade those polypeptide. So many proteins are acetylated at the terminal amino groups to prevent degradation by our cells. So if we go to the beginning of our polypeptide, the nitrogen is basically modified by adding this acetal group. And what that does is it prevents this polypeptide from being broken down. Now, another way by modifying proteins is by adding on hydroxyl groups. And one common example is Collagen.