Amino acids all have a carboxyl group (-COO-) and an amino group (-NH3+) are covalently bound to a central carbon atom (the α-carbon).

The side chain or R- group differs between amino acids.

Amino acids are covalently bonded to one another via a peptide bond between the carboxyl group of one amino acid and the amino group of a second.

The side chains of the amino acids contribute to the charge seen on the protein, which contributes to the folding and function of the protein.

• The isoelectric point (pI) is the pH at which a protein has no overall net charge.

• Acidic proteins contain many negatively charged amino acids and have a low pI.

• Basic proteins contain many positively charged amino acids and have a high pI.

The three-dimensional shape of a protein dictates the properties and function of the protein.

The pKa value given for the amino group on any amino acid specifically refers to the equilibrium between the protonated positive nitrogen and deprotonated neutral nitrogen.

If the pH of the solution < the pK value, then the group will be protonated.
If the pH of the solution > the pK value, then the group will be deprotonated.