Which hormone act by crossing cell membrane -
(A) Thyroxine (B) Insulin (C) Glucagon (D) Calcitonin
(A) Ans. A. ThyroxineIntracellular receptors are transcription factors that have binding sites for the hormone (ligand) and for DNA and function as ligand (hormone)-regulated transcription factors.Steroid hormones and the steroid derivative vitamin D3 fulfill this requirement.Thyroid hormones must be actively transpoed into the cell.