Question

Illustrate the differences between the mechanism of action of a protein and a steroid hormone.

Answer 1

Solubility in water:

Protein hormones are soluble in water, however, steroid hormones are insoluble in water.

Solubility in lipid:

Protein hormones are insoluble in lipids, however, steroid hormones are soluble in lipids.

Entry into cell :

The mode of entry into the cells depends upon the solubility of the hormone.

• Protein hormones cannot enter the cell as they are water soluble and the cell membrane is composed of phospholipid bilayer.
• Steroid hormones being soluble in lipids can easily penetrate the cell membrane.

Types of receptors:

Hormones work by binding to their receptors. Binding of the hormone and receptor forms the hormone-receptor complex.

• Protein hormones usually have membrane-bound receptors.
• The steroid hormones have the receptors located inside the cell (intracellular receptors).

Mechanism of action:

• Protein hormones after binding with membrane receptors generate secondary messengers like $C{a}^{2+}$ , IP3, cAMP which bring about biochemical and physiological changes.
• Steroid hormones after binding with intracellular receptors interact with the genetic material regulating its expression.