Hormones derived from protein, peptides, or amino acids that cannot easily cross cell membranes are known as

• A. Steroid hormones
• B. Amine hormones
• C. Peptide hormones
• D. Nonsteroid hormones

Answer: (D)

Proteins, peptides, and amino-acid–derived hormones are typically water-soluble, so they don’t cross the cell’s lipid membrane easily. Because they can’t slip inside the cell, they bind to receptors on the cell surface and trigger signaling cascades inside the cell using second messengers like cAMP or IP3/DAG. This leads to rapid cellular responses without directly changing gene transcription. Steroid hormones, in contrast, are lipid-soluble and can cross the membrane to act on intracellular receptors, often altering gene expression. Since these hormones cannot readily cross membranes, they fit the nonsteroid hormone category, which includes many peptide and amine hormones.