The structure of glycine is #"H"_3 stackrel("+")("N")"CH"_2"COO"^"-"#.
Glycine has two #"p"K_text(a)# values: #"p"K_text(a1) = 2.34# for the carboxylic acid and #"p"K_text(a2) = 9.60# for the amine.
At the isoelectronic point (#"p"I#), the structure is electrically neutral.
#"p"I = ("p"K_text(a1) + "p"K_text(a2))/2 = (2.34 + 9.60)/2 = 11.94/2 = 5.97#
Below #"pH 5.97"#, glycine will have a net positive charge, while above #"pH 5.97"#, glycine will have a net negative charge.
Within #"±1.5 pH"# unit of #"pI"#, (i.e. from #"pH 4.5 to 7.5"#) glycine exists almost entirely in the neutral form (I calculated a net charge of +0.004 at #"pH 5"#).
I used Wolfram Alpha to calculate the net charge on glycine as a function of #"pH"#.
Here's what I got.
