I. Biological actions of Thyroid Hormones T, and T, bind with nuclear receptor, activate and initiate genetic transcription mrNA protein syntheSis in cytoplasmic ribosomes general increase in functional activity throughout the body.I. Biological Actions of Thyroid Hormones ◼ T3 and T4 bind with nuclear receptor, ◼ activate and initiate genetic transcription. ---- mRNA ◼ protein synthesis in cytoplasmic ribosomes ---- ◼ general increase in functional activity throughout the body