Question

The isoelectric point of an amino acid is : (1) The \(\mathrm{pH}\) at which it exists in the acidic form (2) The \(\mathrm{pH}\) at which exists in the basic form (3) The \(\mathrm{pH}\) at which it exists in the Zwitterion form (4) The \(\mathrm{pH}\) which is equal to its \(\mathrm{pK}_{\mathrm{a}}\) value

Short answer

The pH at which an amino acid exists in the zwitterion form.

Step-by-step solution

Understand the Isoelectric Point

The isoelectric point (pI) is the \(\text{pH}\) at which a particular molecule carries no net electrical charge.

Identify the Forms of an Amino Acid

Amino acids can exist as cations (positively charged) in acidic solutions, anions (negatively charged) in basic solutions, or as zwitterions (having both a positive and a negative charge but overall neutral) at their isoelectric point.

Definition of Zwitterion Form

The zwitterion form is the form in which the amino acid has no net charge, meaning the positive and negative charges balance each other out.

Answer the Question

Based on the definitions and understanding, the correct answer is the pH at which the amino acid exists in the zwitterion form.

Key concepts

amino acids

Amino acids are the building blocks of proteins. They contain an amino group \[\mathrm{-NH_2}\] and a carboxyl group \[\mathrm{-COOH}\], along with a side chain specific to each amino acid. These side chains can be non-polar, polar, or charged, affecting the amino acid's properties.
Amino acids are crucial for numerous biological processes, such as enzyme function, cellular signaling, and protein synthesis.
Understanding amino acids is key to grasping more complex biochemical concepts.

Amino acids can:

• Exist as cations in acidic conditions
• Exist as anions in basic conditions
• Act as zwitterions around their isoelectric point (pI)

zwitterion

At a specific \(\text{pH}\), amino acids exist in a zwitterion form. This means they have both a positive and a negative charge within the same molecule, making the overall charge neutral.
The amino group (\