Final answer:
Steroid hormones are lipid-based, fat-soluble molecules that affect target cells by entering them and influencing gene expression, while nonsteroid hormones are amino acid-based, not fat-soluble, and work by binding to receptors on cell membranes, activating internal signaling pathways.
Step-by-step explanation:
The main difference between steroid and nonsteroid hormones lies in their chemical structure and the mechanism by which they affect target cells within the endocrine system. Steroid hormones are made of lipids, and because they are fat-soluble, they can diffuse across the plasma membrane of target cells. Once inside, they bind to specific receptor proteins in the cytoplasm or nucleus and influence gene expression. Examples include cortisol and sex hormones like estrogen.
Nonsteroid hormones, on the other hand, are made from amino acids and are not fat-soluble. These hormones cannot diffuse through the plasma membrane. Instead, they bind to receptor proteins on the cell membrane, activating an enzyme that stimulates a second messenger molecule inside the cell, influencing internal cell processes. Insulin and thyroid hormones are examples of nonsteroid hormones.