Proteins are polymers made up of amino acids. This produces a charged but electically neutral zwitterion. Figure 3.4a from the textbook. Shown are ball and stick, and molecular formula models of the molecules. Figure 3.4b from the textbook.
All amino acids have fairly similar pKA's for their carboxyl and amino groups.
Zwitterions have both positive and negative charges, but no net charge and are electrically neutral. Figure 3.07 from the text. The sequence, or order, of a protein is depicted by the amino acids starting from the amino end and ending at the carboxyl end. A number of hormones are peptides. The structure of the peptide bond ensures that its atoms are in the same plane and probits rotation about the peptide bond.