Amino acids are the molecules that form proteins when linked with covalent bonds. Amino acids are organic compounds that contain both amino and carboxyl functional groups. They are the basic units of protein and are essential for the structure and function of proteins. Amino acids are linked together by peptide bonds, which are covalent bonds formed between the amino group of one amino acid and the carboxyl group of another amino acid. The sequence of amino acids in a protein determines its unique structure and function. Proteins are essential for many biological processes, such as metabolism, growth, and reproduction. They are also found in hair, skin, and nails.