Which class of molecules do insulin and estrogen belong to?

• A. Enzymes
• B. Hormones
• C. Nucleic acids
• D. Lipids

Answer: (B)

Insulin and estrogen are signaling molecules that travel through the bloodstream to affect distant cells, which is the defining role of hormones. As hormones, they regulate essential processes like glucose metabolism and reproductive development by binding to specific receptors on target cells and triggering responses. Enzymes are catalysts that speed up chemical reactions, which is a different function. Nucleic acids store and transmit genetic information, which they do not do. Lipids include fats and related molecules; while some hormones (like estrogen) are chemically derived from lipids, the term that best captures their role in the body is hormones. So both insulin and estrogen belong to the hormone class.