Water is an important transport and reaction medium
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Answer:
The answer would be Hydrophobic tail and a hydrophilic head. Just some background info, this is located in the cell membrane and the cell membrane is made of up something called the Lipid Bilayer. The word "bi" means 2, so it comprise of 2 layers of phospholipids. These 2 layers of phospholipids are called hyrodrohpbic and hydrophilic. The word "phobic" means fear, so they hydrophobic molecules are NOT attracted to water. Hydrophilic molecules, however, ARE attracted to the molecules.
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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 <em>hydrophilic</em> 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 <em>G-coupled proteins; </em>examples of signals that cascade down the cell are cylic AMP and cyclic GMP.
