The pK_a values for the three ionizable group | vedclass

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Question

(B) Glutamic acid is an acidic amino acid with three ionizable groups: two carboxylic acid groups $(-COOH)$ and one amino group $(-NH_3^+)$.The $pK_a$

Vedclass · Accepted Answer

$3.25$

Vedclass · Answer

(B) Glutamic acid is an acidic amino acid with three ionizable groups: two carboxylic acid groups $(-COOH)$ and one amino group $(-NH_3^+)$.The $pK_a$ values are given as $2.2$ (for the $\alpha-COOH$),$4.3$ (for the side chain $-COOH$),and $9.7$ (for the $-NH_3^+$ group).The isoelectric point $(pI)$ of an acidic amino acid is calculated by taking the average of the two lowest $pK_a$ values:$pI = \frac{pK_{a1} + pK_{a2}}{2} = \frac{2.2 + 4.3}{2} = \frac{6.5}{2} = 3.25$.

The $pK_a$ values for the three ionizable groups $X, Y$ and $Z$ of glutamic acid are $4.3, 9.7$ and $2.2$ respectively. The structure is $HO_2C-CH_2-CH_2-CH(NH_3^+)-CO_2H$. The isoelectric point $(pI)$ for this amino acid is:

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