Methionine, one of the 20 amino acid building blocks from which proteins are made, has the following structure. What is the chemical formula of methionine? In writing the for-mula, list the element symbols in alphabetical order, and give the number of each element as a subscript.

Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid contains a central carbon atom, an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group) that determines its unique properties. Methionine is one of the 20 standard amino acids and is characterized by its sulfur-containing side chain.

A chemical formula represents the composition of a molecule, indicating the types and numbers of atoms present. In the case of amino acids, the formula is derived from counting the atoms of each element in the structure. For methionine, the formula must be written with element symbols in alphabetical order, with subscripts denoting the number of each type of atom.

Element symbols are one- or two-letter abbreviations for chemical elements, such as C for carbon, H for hydrogen, O for oxygen, and N for nitrogen. In a chemical formula, subscripts are used to indicate the number of atoms of each element in a molecule. For example, in the formula C3H7NO2, the subscript '3' indicates there are three carbon atoms, while '7' indicates seven hydrogen atoms.