Basic amino acids primarily react through the formation of peptide bonds via a condensation reaction, and through interactions mediated by their basic side chains.
Peptide Bond Formation
The most fundamental reaction of amino acids is the formation of peptide bonds. This process links amino acids together to form peptides and proteins.
- Condensation Reaction: The carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH2) of another amino acid.
- Water Molecule Release: During the reaction, a molecule of water (H2O) is released.
- Peptide Bond Formation: The resulting bond between the two amino acids is called a peptide bond (an amide bond).
This can be represented as:
Amino acid 1 - COOH + Amino acid 2 - NH2 --> Amino acid 1 - CO - NH - Amino acid 2 + H2O
Reactions Involving Basic Side Chains
Basic amino acids (Lysine, Arginine, and Histidine) possess side chains that are positively charged at physiological pH. This allows them to participate in a variety of reactions:
- Acid-Base Reactions: The basic side chains can accept protons (H+), acting as bases in chemical reactions. This is particularly relevant for Histidine, which has a pKa close to physiological pH, making it effective in enzyme catalysis.
- Salt Bridge Formation: The positively charged side chains can interact with negatively charged molecules, such as the side chains of acidic amino acids (Aspartic acid and Glutamic acid), forming salt bridges. These electrostatic interactions contribute to protein structure and stability.
- Hydrogen Bonding: The amino groups in the side chains can participate in hydrogen bonding with other molecules.
- Metal Ion Coordination: Histidine can coordinate with metal ions, which is important in the function of some metalloproteins and enzymes.
- Post-translational Modification: Lysine is often the target of post-translational modifications such as acetylation and methylation, which can alter protein function and interactions. Arginine can also be modified by methylation and citrullination.
Summary
In summary, basic amino acids react primarily through peptide bond formation and through reactions mediated by their basic side chains. These reactions are crucial for protein synthesis, structure, function, and interactions.
