How do steroid model and protein model for hormone differ?

Question

How do steroid model and protein model for hormone differ?

Answer 1

steroid hormones have intracellular receptors inside the cytoplamic of the cells which combines with the steroids and form a complex which then binds with the HRE (Hormone response element) on the DNA in the nucleus. Even thyroid hormones act in the same way as steriod hormones whereas most protein hormones bind to the receptors present on the memberane receptors on the cytoplasmic cell memberane on the cell. Here they stimulate a cascade pathway mediated by second messengers such as cAMP or calmodulin and this in turn activate the proteinkinases which brings about the various cellular response.

Answer 2

Steroid hormones typically have intracellular (sometimes intranuclear) receptors.  Since steroids are lipophilic and can cross membranes easily, this works quite well. Protein hormones can't cross membranes because of their hydrophilic portions, so they usually are ligands for membrane-bound receptors (cell surface or transmembrane).  Protein hormones are also typically much larger than steroid hormones.