Amino acids
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What is a zwitterion?
A zwitterion is an amino acid molecule with both a positive and negative electrical charge. This occurs when the amino group is protonated (NH₃⁺) and the carboxyl group is deprotonated (COO⁻).
Define the isoelectric point (pI) of an amino acid.
The isoelectric point (pI) is the pH at which a particular amino acid exists predominantly as a zwitterion. At this pH, the amino acid has no net electrical charge and will not migrate in an electric field.
Describe how amino acids behave in acidic conditions (pH < pI).
In acidic conditions (pH < pI), amino acids act as bases and accept protons. The amino group (NH₂) becomes protonated (NH₃⁺), and the amino acid carries a net positive charge (+1).
Describe how amino acids behave in alkaline conditions (pH > pI).
In alkaline conditions (pH > pI), amino acids act as acids and lose protons. The carboxyl group (COOH) becomes deprotonated (COO⁻), and the amino acid carries a net negative charge (-1).
Describe the formation of a peptide bond.
A peptide bond (amide bond) is formed via a condensation reaction between the carboxyl group of one amino acid and the amino group of another. This reaction releases a water molecule (H₂O).
What is a dipeptide?
A dipeptide is a molecule consisting of two amino acids joined by a single peptide bond.
What is electrophoresis and how can it be used to separate amino acids?
Electrophoresis is a technique that separates charged molecules based on their size and charge by applying an electric field. Amino acids migrate towards the electrode with the opposite charge, with the separation dependent on their pI and the buffer pH.
Predict the direction of movement of an amino acid during electrophoresis if the pH of the buffer is less than the amino acid's pI.
If the pH < pI, the amino acid will be positively charged overall. Therefore, it will migrate towards the cathode (negative electrode).
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