Water-soluble hormones affect target cells by binding to which of the following?

• A. membrane-bound receptors
• B. nuclear receptors
• C. mitochondrial membranes
• D. cytoplasmic enzymes

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the nature of water-soluble hormones. These hormones are hydrophilic, meaning they cannot pass through the lipid bilayer of the cell membrane. This is a key characteristic that determines how they interact with target cells.
2. Step 2: Recall the mechanism of action for water-soluble hormones. Since they cannot enter the cell directly, they bind to receptors located on the cell membrane. These receptors are specifically designed to recognize and respond to water-soluble hormones.
3. Step 3: Compare the options provided in the question. Evaluate each option based on the mechanism of action for water-soluble hormones: (a) membrane-bound receptors, (b) nuclear receptors, (c) mitochondrial membranes, and (d) cytoplasmic enzymes.
4. Step 4: Eliminate incorrect options. Nuclear receptors are typically associated with lipid-soluble hormones like steroid hormones, which can pass through the cell membrane. Mitochondrial membranes and cytoplasmic enzymes are not directly involved in the initial binding of water-soluble hormones.
5. Step 5: Conclude that water-soluble hormones affect target cells by binding to membrane-bound receptors, as this aligns with their inability to cross the cell membrane and their reliance on extracellular signaling mechanisms.