Final Answer:
Lipid-soluble signal molecules, such as steroid hormones, bind to intracellular receptors. These receptors are often located within the cell, typically in the cytoplasm or nucleus, due to the hydrophobic nature of the signal molecules, allowing them to traverse the plasma membrane.
Step-by-step explanation:
Intracellular receptors are specialized proteins located within the cell, and they play a crucial role in mediating responses to lipid-soluble signal molecules. Lipid-soluble molecules, including steroid hormones (e.g., estrogen, testosterone, cortisol), are hydrophobic and can easily traverse the lipid bilayer of the plasma membrane.
Unlike water-soluble signal molecules that bind to cell surface receptors, lipid-soluble molecules do not need a cell surface receptor. Instead, they pass through the plasma membrane and bind directly to intracellular receptors in the cytoplasm or nucleus.
The binding of the lipid-soluble signal molecule to its intracellular receptor induces a conformational change in the receptor, activating it. This activated receptor-signal complex can then translocate to the nucleus (if it wasn't already there) and act as a transcription factor, regulating gene expression.
The genes affected by these intracellular receptors often play critical roles in various cellular processes, including growth, differentiation, and metabolism. Understanding the mechanisms of intracellular receptor signaling is essential for comprehending how cells respond to lipid-soluble signaling molecules and how these signals contribute to physiological homeostasis and cellular functions.