Phosphorylation and Serine Properties

In living organisms, biomolecules such as proteins, carbohydrates, and lipids play crucial roles in various biological processes. Proteins, made up of amino acids, can function as enzymes, structural components, or signaling molecules. Each amino acid has a specific side chain that dictates its properties and functions. A common structural characteristic of amino acids is the presence of an amine group (-NH₂), a carboxylic acid group (-COOH), and a unique R group that varies among different amino acids.

Consider the following scenario: A team of researchers is investigating a protein that is involved in metabolic pathways. They discover that a specific amino acid in this protein is frequently modified post-translationally. This modification involves the addition of a phosphate group to the hydroxyl group of a serine residue. This process is known to alter the protein’s activity and can affect its interaction with other biomolecules.

Which of the following amino acid characteristics best explains the ability of serine to undergo this modification?