At a pH equal to the isoelectric point of alanine, the net charge on alanine is zero. Two structures can be drawn that have a net charge of zero, but the predominant form of alanine at its pI is...

At a pH equal to the isoelectric point of alanine, the net charge on alanine is zero. Two structures can be drawn that have a net charge of zero, but the predominant form of alanine at its pI is zwitterionic.
(a) Why is alanine predominantly zwitterionic rather than completely uncharged at its pI?
(b) What fraction of alanine is in the completely uncharged form at its pI? Justify your assumptions.