. "\"The chemical reactions and pathways leading to the formation of tetrapyrroles, natural pigments containing four pyrrole rings joined by one-carbon units linking position 2 of one pyrrole ring to position 5 of the next.\" [CHEBI:26932, GOC:mah]" . . "tetrapyrrole biosynthetic process" . "tetrapyrrole anabolism" . "tetrapyrrole biosynthesis" . "tetrapyrrole formation" . "tetrapyrrole synthesis" . . . . . . .