Question

A mechanism through which a cell reponds to a nonpolar signaling molecule is quite different from the way a cell reponds to a polar signaling molecule. for this question focus on the way a cell responds to a nonpolar signaling molecule such as a steroid hormone. summarize this process, starting with a steroid hormone in the bloodstream, up to the major response in the target, responding cell.

Answer 1

The plasma membrane is made up of lipid bilayer and is selectively permeable to the small polar molecules and the hydrophobic molecules. Ions and large polar molecules are not able to traverse through the plasma membrane.

The peptide hormones like epinephrine are not lipid-soluble (lipid-derived). The receptors for the peptide hormones are present on the cell surface. The peptide hormones bind to its receptors to generate the second messenger (cAMP) that initiates the enzymatic pathway to generate a response.

The action of a polar signaling molecule (peptide hormones like epinephrine) is shown below:

Therefore, the peptide hormone cannot traverse through the plasma membrane.

The steroid hormones are lipid-derived and lipid-soluble. They cross the plasma membrane and bind to its receptors in the nucleus or the cytoplasm and form a hormone-receptor complex that further generates the desired response.

The action of a nonpolar signaling molecule (steroid hormones) is shown below:

Therefore, the steroid hormone can traverse along the cell membrane.