Serine is classified as a polar amino acid. This is primarily due to the presence of a hydroxyl (-OH) group in its side chain. The electronegative oxygen atom in the hydroxyl group attracts electrons, creating a dipole moment and allowing serine to form hydrogen bonds with water and other polar molecules.
In biochemical contexts, this polarity plays a crucial role in the structure and function of proteins. Polar amino acids like serine are often found on the surface of proteins, where they can interact with the aqueous environment, facilitating various biochemical reactions.
Thus, the presence of the hydroxyl group is what makes serine polar, allowing it to participate in essential biological functions.