Glycine is the simplest amino acid there is. Its structural formula is shown in the attached picture. Amino acids are characterized with having an amine group and a carboxylic group at both ends of the terminals. Carboxylic acid is acidic so it has a partial negative charge on one side. Amines are basic so it has a partially positive charge on the other side. Possessing this property of having opposite charges at once is called a zwitterion. That is what is meant by the pKa values. These are the pH values of the individual functional groups. The pKa 2.34 is for the carboxylic group while pKa 9.6 is for the amine group.
These electrostatic attractions depend on the pH of the solution. At pH 12, the functional group that predominates is the carboxylic group with an overall charge of -1 as shown in the second picture.
