Some hormones bind to membrane receptors and others bind to intracellular receptors. Hormones that bind to intracellular receptors tend to be
The correct answer and explanation is:
Hormones that bind to intracellular receptors tend to be lipid-soluble (hydrophobic).
Explanation:
The location of a hormone’s receptor is determined by the hormone’s chemical properties, specifically its solubility in lipids versus water. Hormones that bind to intracellular receptors must be able to cross the cell membrane to reach their receptors located within the cytoplasm or nucleus.
Cell membranes are composed primarily of a lipid bilayer. This structure acts as a barrier, preventing the free passage of water-soluble (hydrophilic) molecules. However, lipid-soluble (hydrophobic) molecules can readily diffuse across this bilayer.
Therefore, hormones that are lipid-soluble, such as steroid hormones (like cortisol, estrogen, testosterone, and aldosterone) and thyroid hormones (T3 and T4), can easily pass through the cell membrane. Once inside the target cell, they bind to specific protein receptors located in the cytoplasm or within the nucleus.
In contrast, water-soluble hormones, such as peptide hormones (like insulin and growth hormone) and catecholamines (like epinephrine), cannot easily cross the lipid bilayer. They must bind to receptors embedded in the cell surface membrane. This binding triggers intracellular signaling pathways (often involving second messengers) to elicit a response, without the hormone itself entering the cell.
Upon binding to an intracellular receptor, the hormone-receptor complex typically translocates to the nucleus (if it wasn’t already nuclear) and binds to specific DNA sequences. This interaction regulates gene expression, leading to changes in the synthesis of specific proteins. This mechanism usually results in cellular responses that are slower in onset but longer-lasting compared to those mediated by membrane receptors.
In summary, the ability to permeate the lipid bilayer dictates that hormones interacting with intracellular receptors must possess significant lipid solubility.