Isoleucine has the zwitterion structure shown. Draw the structure and give the net charge of isoleucine that will predominate at the indicated pH values (pI = 6.0).


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b. pH 6.0

Verified step by step guidance

1. Identify the structure of isoleucine in its zwitterion form. A zwitterion is a molecule with both positive and negative charges, but an overall neutral charge.
2. Understand that the isoelectric point (pI) is the pH at which the amino acid exists predominantly in its zwitterion form. For isoleucine, the pI is given as 6.0.
3. At pH 6.0, which is equal to the pI, isoleucine will predominantly exist in its zwitterion form. This means the amino group (NH3+) is protonated, and the carboxyl group (COO-) is deprotonated.
4. Draw the structure of isoleucine at pH 6.0, showing the NH3+ group and the COO- group. The side chain remains unchanged as it does not participate in the zwitterion formation.
5. Determine the net charge of isoleucine at pH 6.0. Since the positive charge on the NH3+ group and the negative charge on the COO- group cancel each other out, the net charge is 0.

Key Concepts

Zwitterion Structure

A zwitterion is a molecule that has both positive and negative charges but is overall neutral. In the case of amino acids like isoleucine, the amino group (–NH3+) carries a positive charge, while the carboxyl group (–COO–) carries a negative charge. This dual charge allows zwitterions to exist in a stable form in solution, particularly at specific pH levels.

Isoelectric Point (pI)

The isoelectric point (pI) is the pH at which an amino acid exists predominantly in its zwitterionic form, resulting in a net charge of zero. For isoleucine, the pI is given as 6.0, meaning that at this pH, the positive and negative charges balance out. Understanding pI is crucial for predicting the behavior of amino acids in different pH environments.

pH and Charge Relationship

The pH of a solution affects the ionization state of amino acids, influencing their net charge. At pH values below the pI, amino acids tend to be positively charged, while at pH values above the pI, they become negatively charged. This relationship is essential for determining the predominant charge of isoleucine at various pH levels, particularly at the specified pH of 6.0.