What is isoelectric point?

Options

A. Specific temperature
B. Suitable concentration of amino acid
C. Hydrogen ion concentration that does not allow migration of amino acid under electric field
D. Melting point of an amino acid under the influence of electric field

Answer

### Step-by-Step Solution:

1. **Definition of Isoelectric Point (pI)**:
- The isoelectric point (pI) is defined as the pH at which a molecule, typically an amino acid or protein, carries no net electrical charge.

2. **Understanding Net Charge**:
- At the isoelectric point, the positive and negative charges within the molecule balance each other out, resulting in a net charge of zero. This means that the molecule is neutral.

3. **Zwitterion Formation**:
- At the isoelectric point, the molecule exists in a form known as a zwitterion. A zwitterion is a molecule that has both positive and negative charges but is overall neutral. For example, an amino acid can exist as a zwitterion where the amino group (-NH3⁺) carries a positive charge and the carboxyl group (-COO⁻) carries a negative charge.

4. **pH and Hydrogen Ion Concentration**:
- The isoelectric point can be mathematically represented as the pH where the concentration of hydrogen ions ([H⁺]) is such that the net charge is zero. This can be expressed using the formula:
\[ pI = -\log[H^+] \]

5. **Behavior in Electric Fields**:
- When a molecule is at its isoelectric point, it does not migrate in an electric field because it has no net charge. Charged molecules will move towards the oppositely charged electrode, but a neutral molecule will not move.

6. **Conclusion**:
- The isoelectric point is crucial in various biochemical processes, including protein purification and characterization, as it helps determine the solubility and stability of proteins.