Question

The following hormone does not have any intracellular receptor:

• A. Vitamin D3
• B. Cortisone
• C. Adrenaline
• D. Thyroxine

Hint:

Steroid and thyroid hormones cross the cell membrane and use nuclear receptors; catecholamines cannot cross it and use surface receptors instead.

Answer 1

The Correct Option is C

Step 1: Understanding the Question.
The question asks which of the four hormones does not need to enter the cell to act. This depends on how each hormone is built and how it talks to its target cell.

Step 2: Key Concept or Approach.
Hormones fall into two broad groups by how they cross the cell membrane. Steroid hormones (cortisone and vitamin D3) and thyroid hormone (thyroxine) are fat soluble. They pass straight through the lipid membrane and bind a receptor sitting inside the cell, in the cytoplasm or nucleus, and this pair then acts on DNA to switch genes on or off. Catecholamines such as adrenaline are water soluble and carry charge, so they cannot cross the membrane. They bind a receptor sitting on the outer cell surface instead, and that receptor sets off a second messenger, mainly cyclic AMP, inside the cell.

Step 3: Detailed Explanation.
Vitamin D3 acts on the nuclear vitamin D receptor, so it works from inside the cell. Cortisone is a glucocorticoid and binds the intracellular glucocorticoid receptor before the complex moves to the nucleus. Thyroxine binds a nuclear thyroid hormone receptor and changes gene transcription directly. Adrenaline is different from these three. It is a catecholamine released from the adrenal medulla, and it binds alpha and beta adrenergic receptors on the outer surface of the target cell. These are G protein coupled receptors, and adrenaline never enters the cell to reach a receptor inside it.

Step 4: Final Answer.
Three of the four hormones work through intracellular receptors. Adrenaline is the one that signals only through a cell surface receptor, so it is the hormone with no intracellular receptor.