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15.2C: Chemistry of Hormones

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  • There are three classes of hormones: peptide hormones, lipid hormones, and monoamine hormones.

    Learning Objectives

    • Distinguish between the hydrophilic and lipophilic types of endocrine hormones based on their chemical structures

    Key Points

    • Peptide hormones are comprised of short (peptides) and long ( proteins ) chains of amino acids. They are water-soluble but cannot pass through the plasma membrane alone.
    • Glyco-protein hormones have a carbohydrate moiety attached to the protein.
    • Lipid hormones include steroid and eicosanoid hormones. They are lipid-soluble and can pass through the plasma membrane.
    • Steroid hormones are derived from the cholesterol and eicosanoid hormones from fatty acids that compose the plasma membrane.
    • The third class of hormones is the monoamines that are derived from aromatic amino acids like phenylalanine, tyrosine, and tryptophan.

    A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism.

    There are three classes of hormones:

    1. Peptide hormones
    2. Lipid-derived hormones
    3. Monoamine hormones

    Peptide Hormones

    Peptide hormones consist of short chains of amino acids, such as vasopressin, that are secreted by the pituitary gland and regulate osmotic balance; or long chains, such as insulin, that are secreted by the pancreas, which regulates glucose metabolism.

    Some peptide hormones contain carbohydrate side chains and are termed glyco-proteins, such as the follicle-stimulating hormone. All peptide hormones are hydrophilic and are therefore unable to cross the plasma membrane alone.

    This is a color illustration of the molecular structure of a peptide hormone.

    Peptide hormone: Representation of the molecular structure of a peptide hormone.

    Lipid-Derived Hormones

    Lipid and phospholipid-derived hormones are produced from lipids such as linoleic acid and arachidonic acid. Steroid hormones, which form the majority of lipid hormones, are derived from carbohydrates; for example, testosterone is produced primarily in the testes and plays a key role in development of the male reproductive system.

    Eicosanoids are also lipid hormones that are derived from fatty acids in the plasma membrane. Unlike other hormones, eicosanoids are not stored in the cell—they are synthesized as required. Both are lipophillic and can cross the plasma membrane.

    Monoamine Hormones

    Monoamine hormones are derived from single aromatic amino acids like phenylalanine, tyrosine, and tryptophan. For example, the tryptophan-derived melatonin that is secreted by the pineal gland regulates sleep patterns.