RNA leader sequences are found upstream of the first gene of amino acid biosynthetic operons. Examples of these biosynthetic pathways include the production of lipid membrane components and nucleotides. P450 monooxygenases are involved in the amygdalin biosynthetic pathway. Genetic deficiencies in the creatine biosynthetic pathway lead to various severe neurological defects. A microbial biosynthetic pathway has been proposed. The biosynthetic genes responsible for rapamycin synthesis have been identified. This suggests independent evolution of the limonene biosynthetic pathway in these two lineages. NADP mainly functions with enzymes that catalyze anabolic, or biosynthetic, pathways. The biosynthetic pathways may differ among organisms. Plants can synthesize IAA by several independent biosynthetic pathways. Anhydrotetracycline contains the first functionalized A ring in this biosynthetic pathway. The biosynthetic pathways are regulated by riboswitches. Natural products may be classified according to their biological function, biosynthetic pathway, or source. Codeine is produced in the human body along the same biosynthetic pathway as morphine. The retrosynthetic analysis was inspired by hyperforin's structural symmetry and biosynthetic pathway.