Question

For each amino acid $\left[\mathrm{RCH}\left({\mathrm{NH}}_2\right)\mathrm{COOH}\right]$, draw its neutral, positively charged, and negatively charged forms. Which form predominates at pH = 1, 6, and 11? What is the structure of each amino acid at its isoelectric point?

a. methionine $\left(R={\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{SCH}}_3\right)$

b. serine $\left(R={\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{OH}\right)$

Short answer

a.

b.

Step-by-step solution

Step 1:Isoelectric point

The isoelectric point represents the pH where no net charge (positive charge balances negative charge) is present.

• The positive form of amino acid is obtained when the acidic medium (low pH) is present.

• The negative form of amino acid is obtained when the basic medium (high pH) is present.

Neutral, positive, and negative

The neutral amino acid has an equal amount of positive and negative charges. The positive form and negative form have positive and negative charges, respectively.

Step 3:Explanation

a. The positive, neutral, and negative methionine is shown as:

For methionine

b. The positive, neutral, and negative serine is shown as:

For serine