Figure 3.15 in the Purves book depicting peptide bond formation seems to conflict with Fig 3.3 in the Becker book. Specifically, why does the amino group pictured in the Purves book have only 2 hydrogens bonded in the free amino group?
Purves (Fig. 3.15) writes the free amino acid prior to peptide bond formation as having an amino group with 2 H's, and uncharged, as it might occur in the solid powder. Becker writes it as it exists predominantly in solution, with 3 H's and a positive charge, having taken up a hydrogen ion from water. He is consistent in writing the carboxyl as also ionized, with no H in sight. Either way, you can extract 2 H's and and O, forming a free water molecule and the peptide bond. Although the ionized form is more accurate, the withdrawal of water is easier to see in the un-ionized form, as I wrote in class. The result is the same. The actual mechanism of peptide bond formation is actually much more complicated than this, as you will soon learn. These reaction schemes merely summarize the molecules that you start with and end up with.