Chemical Classification of Hormones and Mechanisms of Action

Vocabulary flashcards covering the chemical classification of steroid and nonsteroid hormones, cell membrane permeability, and intracellular vs. plasma membrane second-messenger signaling pathways.

Nonsteroid Hormones

A major class of hormones derived from amino acids (including amine, peptide, and protein hormones) that are water soluble and membrane insoluble, requiring them to bind to membrane-bound receptors.

Steroid Hormones

A major class of hormones derived from lipids that are lipid soluble, allowing them to cross the lipid bilayer of cell membranes and nuclear membranes without assistance.

Red Phosphate Heads

The hydrophilic (water-loving) portions of the phospholipid bilayer that face the outer and inner water-rich environments of the cell membrane.

Yellow Fatty Acid Tails

The hydrophobic (water-disliking) middle layer of the phospholipid bilayer that prevents water-soluble substances from crossing the membrane.

Receptor-Hormone Complex (Steroid Pathway)

A complex formed in the cytoplasm or nucleus when a lipid-soluble hormone binds its receptor, which then activates a specific gene on DNA to trigger transcription of mRNA and translation into an active protein.

Half-Life of Steroid Hormones

The duration of $60$ to $90\text{ minutes}$ required for half of a steroid hormone to be eliminated, taking twice that time to fully end its action.

Steroid Hormone Examples

Hormones that utilize lipid-soluble mechanisms, including testosterone, estrogens, progesterone, aldosterone, and cortisol.

$T_3$ and $T_4$

Triiodothyronine ($T_3$) and tetraiodothyronine ($T_4$, also called thyroxine), which are amino acid-derived hormones that act more like lipid-soluble steroid hormones.

First Messenger

The water-soluble nonsteroid hormone that binds to a membrane-bound receptor on the exterior of a target cell membrane.

G Protein

A membrane-associated protein that is activated inside the cell upon the formation of a water-soluble hormone-receptor complex.

Adenylyl Cyclase

An enzyme on the cell membrane (also called adenylate cyclase) activated by a G protein that dephosphorylates ATP to convert it into cyclic AMP.

Cyclic AMP (cAMP)

The second messenger in the water-soluble hormone pathway, synthesized from ATP by adenylyl cyclase.

Protein Kinases

Cytoplasmic enzymes activated by cyclic AMP (cAMP) that phosphorylate existing inactive proteins to turn them into functional activated proteins.

Half-Life of Water-Soluble Hormones

A short duration of approximately $1\text{ minute}$ for half of the hormone to be cleared, with its action fully completing in about $2\text{ minutes}$.

Epinephrine

A water-soluble nonsteroid hormone associated with the sympathetic nervous system response that functions via membrane-bound receptors.