Chemical Characteristics of Hormones

<h1>Text Preview</h1> <p>Although many different hormones have been identified, hormones can be classified into two groups. Hydrophilic, or “water loving,” molecules include amines, peptides, and proteins. Lipophilic, or “lipid-loving,” molecules include steroids and prostaglandins.</p> <p>Hydrophilic hormones are soluble in water and mediate a faster response than lipophilic hormones. The receptors for these hormones are found on the surface of their target cells. The hydrophilic hormone insulin was the first protein whose amino acid sequence was determined. We’ll learn more about the role if insulin later.</p> <p>Local regulators are chemical signals that act on cells very close to the site of release. They never reach high concentrations in the bloodstream. Nerve growth factor is an example of a peptide local regulator. This hormone is critical for the differentiation and survival of nerve cells.</p> <p>Lipophilic hormones, such as the steroid hormones cortisol and testosterone, consist of carbon chains and rings that are soluble in lipids. Their lipophilic nature makes them almost insoluble in blood, so they are bound to carrier proteins in the bloodstream. Lipophilic hormones pass through the lipid bilayer of the cell membrane. Once inside the cell, they bind to receptors in the cytoplasm or the nucleus. Thyroid hormones, like thyroxine, are lipophilic hormones derived from amino acids. They consist of two amino acids that are modified with iodine. This modification makes them lipophilic. </p> <p>Prostaglandins are lipophilic local regulators. They act on cells close to the cell that synthesized them, and don’t reach high concentrations in the blood. Retinoids also act as local regulators. You may be familiar with the use of retinoic acid to promote the local growth of new skin cells.</p> <p>Now that we can identify the different types of hormones, let’s explore how hormones affect cellular activities.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>