AP BIOLOGY

Detailed explanation-1: -Small, hydrophobic ligands can pass through the plasma membrane and bind to intracellular receptors in the nucleus or cytoplasm. In the human body, some of the most important ligands of this type are the steroid hormones.

Detailed explanation-2: -Hydrophobic signaling molecules ( ligands ) can diffuse through the plasma membrane and bind to internal receptors.

Detailed explanation-3: -These intracellular receptors respond to small hydrophobic signaling molecules that are able to diffuse across the plasma membrane. The steroid hormones are the classic examples of this group of signaling molecules, which also includes thyroid hormone, vitamin D3, and retinoic acid (Figure 13.2).

Detailed explanation-4: -The two main groups of receptors binding hydrophobic ligands are lipid receptors and steroid receptors and they all belong to class A GPCRs.

Detailed explanation-5: -Although most extracellular signals are hydrophilic molecules that bind to receptors on the surface of the target cell, some signal molecules are hydrophobic enough and/or small enough to pass readily across the target-cell plasma membrane.