The structure of a peptide is given below 

If the absolute values of the net charge of the peptide at pH = 2, pH = 6, and pH = 11 are |z₁|, |z₂| and|z₃| respectively, then what is |z₁| + |z₂| + |z₃| ?

|z₁| + |z₂| + |z₃| = 5
 

At pH = 2 $\stackrel{1}{{\mathrm{NH}}_2}$ and $\stackrel{2}{{\mathrm{NH}}_2}$of tyrosine and lysine are positively charged (+1 each) +2 |z₁| = 2
At pH = 6, NH₂ of Lysine (+1), COOH (–1) of
glutamic aicd, so because of dipolar ion, |z₂| = 0
At pH = 11, COOH of glutamic acid (–1)
COOh of phnol(–1)
OH of phenol (–1)
$\therefore \left|{\mathrm{z}}_3\right|=3$