The subunits of virtually all organic molecules are joined by dehydration reactions and can be broken?

Question

The subunits of virtually all organic molecules are joined by dehydration reactions and can be broken apart by hydrolysis reactions. Why then does your digestive system produce separate enzymes to digest fats, proteins, and carbohydrates?

Answer 1

Although carbohydrates, proteins, and, fats are all made from their precursor molecules by dehydration reactions, the precursors are different. An amino acid looks very different from a simple sugar. So the enzymes that break them down are different for two major reasons: First, enzymes generally recognize the shape of the substrates they break down, so a protease needs to recognize a part of a protein (which has a different shape than a part of a carbohydrate). Second, although the bonds between parts of proteins and carbohydrates are both formed by removing a water molecule, the bonds are between different organic groups. In proteins, you have a series of peptide linkages between amine nitrogens and carboxylic acids; whereas, between carbohydrates you have a bond between two carbon atoms - one with an alcohol group, and one that is participating in a hemiacetal group. In other words, the energy of the bonds is different in the two different types of bio-molecules.