Question

Hormones such as calcitonin, parathyroid hormone, and the pituitary hormones are protein-based and water-soluble. how does a hormone that cannot penetrate the lipid membrane effect change in the cell? drag and drop the events pictured into the correct order from left to right.

Answer 1

The phospholipid bilayer has two hydrophilic surfaces: the extracellular and the intracellular surfaces. These two layers sandwiches a major layer of lipids or fat. Because of this nature of the lipid bilayer, water-soluble or hydrophilic  hormones cannot enter the cell membrane. They have to rely on the mechanisms of receptors.

One can find transmembrane proteins embedded across the whole length of the lipid bilayer. One of the functions of these proteins is to serve as the link for hormones such as the ones given above. When the water-soluble hormones attach to one of these receptors, the receptor will be activated and send down a signal to the intracellular environment; these signals will then travel down towards their target site and eventually activate whatever it is the hormone was made for. One example of these transmembrane proteins are G-coupled proteins; examples of signals that cascade down the cell are cylic AMP and cyclic GMP.