Explain why glutamic acid (pI = 3.08) elutes before threonine (pI = 5.60)  when their solution having pH 5 is passed through a cation-exchange column.

Explain why cysteine (pI = 5.15) elutes before isoleucine (pI = 5.60) when their solution having pH 5 is passed through a cation-exchange column.

Determine whether alanine (pI = 6.11) or serine (pI = 5.70) has a higher percentage of negative charge at pH 7.0.

Is the following statement true or false? 

The amino acid with the lowest pI value is alanine.

The pI of glutamic acid is equal to the average pK_a of its two negatively charged carboxyl groups. Explain.

Draw the structure of the prominent form of lysine (PI 9.7) present at pH values of 6, 9.7, and 12.