Chemical Classes of Hormones

Chemical Classes of Hormones

Author: Aaron Mullally

- know what the two classes of hormones are

- define the term peptide

- define the term polar

define the term non-polar

- give examples of hormones that fall into these classes

- know what steroid hormones are synthesized from

- know what cholesterol is

- know how each class of hormone is transported in the blood stream

- know what a carrier protein is

- know what half life is

This packet covers the two classes of hormones in the human body and their differences.

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There are two major chemical classes of hormones, peptides (proteins) and steroid hormones. Protein based hormones can be divided into three categories: proteins, peptides and amines. Their differences are essential with their size and what they are synthesized from. Peptides are compounds that consist of two or more amino acids; proteins are compounds that consist of 50 or more amino acids; amines are synthesized from the amino acid tyrosine. Another key difference between these are their chemistry. Most of these are polar, meaning they carry a charge (except for thyroid hormones). Their polarity makes it easy for transportation in the blood stream. These hormones diffuse directly into the plasma (water) of the blood and are circulated to their target tissues. This however affects their half life. Half life is the amount of time it takes to degrade to 50%. Unbound hormones have a shorter half life, meaning they are broken down and cleared more rapidly. Thier polarity however makes it impossible for them to cross the cell membrane and directly interact within the cell. These hormones bind to surface receptors on the plasma membrane and activate what are called secondary messener systems.

All steroid hormones are synthesized from the lipid cholesterol. Steroid hormones are just modified cholesterol backbones (see video for examples). These hormones are nonpolar, which means they do not have a charge. Since lipids (and thryoid hormone) are nonpolar they don't react with water very well and have to be transported differently. These hormones are bound to carrier proteins in the plasma, mainly albumin. Once they reach their target tissues they disassociate (detach) from their carriers. Because these are nonpolar they can cross the cell membrane and directly interact within the cell. These hormones bind to nuclear receptors on the nuclear envolope and effect protein synthesis. These hormones also have a longer half life and clear out more slowly than their polar counterparts.

Here is a useful link to see this material in action: http://www.physiol.med.uu.nl/interactivephysiology/ipweb/systems/buildframes.html?endocrine/biosec/01

Source: Mind of Aaron

Chemical Classes of Hormones

This video covers the chemical classes of hormones and offers a basic biochemistry review of lipids and peptides

Source: Self made