Systems Biology
Amino acid-derived hormones play a crucial role in various bodily functions. The four most important amino acid-derived hormones are epinephrine, norepinephrine, and the thyroid hormones T3 and T4. Both epinephrine and norepinephrine, also known as adrenaline and noradrenaline, are catecholamines, a group of signaling molecules derived from the amino acid tyrosine. They are synthesized in the adrenal medulla, the inner region of the adrenal glands, and share very similar biochemical pathways. When these catecholamines reach their target cells, they bind to receptors on the surface of their target cells, which are part of the G-protein-coupled receptor (GPCR) family.
Triiodothyronine (T3) and thyroxine (T4) are amino acid-derived hormones made by the thyroid gland. Both are synthesized in the thyroid follicular cells and the follicular lumen. T3 and T4 are derived from the amino acid tyrosine and are created when tyrosine residues become covalently bound to iodine. T3 and T4 move through the bloodstream, gain entry into cells via transporter proteins in the plasma membrane, and can elicit cellular responses in two ways: genomic and non-genomic action. Thyroid hormones affect cellular metabolism and have the ability to change the body's metabolic rate, impacting how the body uses glucose and fatty acids.
Lesson Outline
<ul> <li>Synthesis and action of the catecholamines, dopamine, epinephrine and norepinephrine <ul> <li>Both are derived from amino acid tyrosine</li> <li>Synthesis occurs in the adrenal medulla</li> <li>L-tyrosine is converted to L-DOPA, L-DOPA is converted to dopamine</li> <li>Dopamine can be further converted to norepinephrine</li> <li>Norepinephrine can be further converted to epinephrine</li> <li>Catecholamines are released into the bloodstream via exocytosis</li> <li>Action on target cells occurs through interaction with GPCRs</li> <li>Ellicit physiological responses via two pathways: cAMP and phospholipase C activation</li> <li>Role in fight, flight or freeze response</li> </ul> </li> <li>Synthesis and action of thyroid hormones T3 and T4 <ul> <li>Derived from amino acid tyrosine</li> <li>Synthesis in thyroid follicular cells and lumen</li> <li>Covalent binding of iodine to tyrosine</li> <li>Three iodines form T3, four iodines form T4</li> <li>Release into bloodstream via facilitated diffusion</li> <li>Action on target cells <ul> <li>Gain entry through transporter proteins</li> <li>Exert effects through genomic and non-genomic pathways</li> <li>Direct gene function alteration (genomic)</li> <li>Activation of second messenger pathways (non-genomic)</li> <li>Affect metabolism and use of glucose and fatty acids</li> </ul> <ul> <li>The names of many amino acid-derived hormones end with "ine"</li>
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FAQs
Amino acid-derived hormones are a class of hormones that are derived from specific amino acids, namely tyrosine and tryptophan. Some examples of amino acid-derived hormones include epinephrine, norepinephrine, and thyroid hormones such as T3 (triiodothyronine) and T4 (thyroxine). These hormones play crucial roles in various physiological processes.
Epinephrine and norepinephrine are synthesized in the chromaffin cells of the adrenal medulla. The process begins with the amino acid tyrosine, which is taken up by these cells and converted into dihydroxyphenylalanine (DOPA) by the enzyme tyrosine hydroxylase. DOPA is then decarboxylated by the enzyme DOPA decarboxylase to form dopamine. Finally, dopamine is converted into norepinephrine by dopamine beta-hydroxylase, and norepinephrine is further methylated by phenylethanolamine N-methyltransferase to form epinephrine.
Epinephrine and norepinephrine bind to specific cell surface receptors called adrenergic receptors, which are a type of G-protein-coupled receptor (GPCR). Upon binding, these receptors activate their associated G-proteins, initiating a series of intracellular signaling cascades involving secondary messengers, such as cAMP or inositol trisphosphate (IP3) and diacylglycerol (DAG). These secondary messengers in turn activate various downstream targets, ultimately leading to physiological responses such as increased heart rate, blood pressure, and metabolic rate.
T3 and T4 thyroid hormones exert their effects on target cells through both genomic and non-genomic mechanisms. The genomic action involves binding to nuclear receptors called thyroid hormone receptors (TRs), which are transcription factors. Upon hormone binding, TRs undergo conformational changes that enable them to bind to specific DNA sequences called thyroid hormone response elements (TREs) in the regulatory regions of target genes. TRs, together with coactivators or corepressors, modulate gene expression, leading to changes in cellular activities such as metabolism, growth, and development. In addition, T3 and T4 can mediate non-genomic actions by binding to cell surface receptors or cytoplasmic targets, which can rapidly activate second messenger pathways to influence cellular functions.
