An amino acid is a simple organic compound that serves as a building block for proteins. Each amino acid contains a central carbon atom, an amino group, a carboxyl group, and a unique side chain, which determines its specific properties. There are 20 different amino acids that combine in various sequences to form proteins, essential for many biological functions. Amino acids are classified into two main categories: essential and non-essential. Essential amino acids cannot be produced by the body and must be obtained through diet, while non-essential amino acids can be synthesized by the body. Foods rich in proteins, such as meat, fish, and beans, are good sources of amino acids.