Receptors for nonsteroid hormones are located in
The Correct Answer and Explanation is:
Correct Answer:
Receptors for nonsteroid hormones are located on the cell membrane.
Explanation
Nonsteroid hormones, also known as peptide or protein hormones, are composed of amino acids and are typically water-soluble. Due to their size and polarity, these hormones cannot pass through the lipid bilayer of the cell membrane. As a result, they bind to specific receptors located on the surface of the target cell’s membrane.
Once a nonsteroid hormone binds to its receptor, it does not enter the cell. Instead, the hormone-receptor interaction triggers a cascade of intracellular events through what is called a second messenger system. The most common second messenger is cyclic AMP (cAMP), though others such as calcium ions and inositol triphosphate (IP₃) may also be involved.
Here is how it works:
- The hormone binds to a receptor protein on the outer surface of the cell membrane.
- This activates a G-protein on the inner side of the membrane.
- The G-protein then activates an enzyme, usually adenylate cyclase, which converts ATP into cAMP.
- cAMP acts as a second messenger to activate various enzymes inside the cell, leading to the desired cellular response.
This method of hormone action is fast-acting and allows for amplification of the signal. Even a small amount of hormone can lead to a significant cellular response due to the multiplication of signals within the cell.
In contrast, steroid hormones are lipid-soluble and can pass directly through the cell membrane. They bind to receptors inside the cytoplasm or nucleus and often influence gene expression directly.
In summary, receptors for nonsteroid hormones are found on the cell membrane because the hormones cannot enter the cell. Their effects are mediated through a second messenger system that leads to a rapid and amplified response.
