Final answer:
ATRA and UTRA are retinoic acids used for medical treatments; ATRA is used to treat acute promyelocytic leukemia by inducing cancer cell differentiation, while UTRA is used for severe nodular acne and has potential anticancer applications.
Step-by-step explanation:
The primary purpose of ATRA (All-trans retinoic acid) and UTRA (13-cis retinoic acid) relates to their roles in medical treatments, specifically in targeting certain types of cancer. ATRA is widely known for its use in the treatment of acute promyelocytic leukemia (APL), where it induces the differentiation of cancerous cell lines into mature granulocytes and leads to the remission of APL. UTRA, also referred to as isotretinoin, is primarily used in the treatment of severe nodular acne, but it is also investigated for its potential anticancer properties.