Which option correctly compares the mechanisms of action of thyroid hormone and insulin at the cellular level?

• A. Thyroid hormone primarily alters transcription after binding intracellular receptors, whereas insulin activates membrane receptor signaling pathways.
• B. Thyroid hormone acts through cAMP second messengers, whereas insulin directly binds DNA regulatory regions.
• C. Thyroid hormone and insulin both enter the nucleus and directly regulate transcription.
• D. Thyroid hormone binds only surface receptors, whereas insulin diffuses through the plasma membrane to cytoplasmic receptors.

Answer: (A)