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Hormone Synthesis
Peptide and protein hormones
Synthesis:
  • Synthesized and then stored in secretory vesicles.
  • First, within the nucleus of a cell, the gene for a hormone is transcribed as mRNA
  • The mRNA moves to the ribosomes, where it is translated to create a preprohormone;
  • The preprohormone moves to the endoplasmic reticulum, where it is converted to a prohormone;
  • Finally, the prohormone is transported to the golgi apparatus to be packaged into secretory vesicles; within these vesicles, peptide cleavage produces the final hormone product.
  • The hormone is stored until its release is triggered.
Transport:
  • Travels freely in the blood; recall that this is because it is water soluble, and readily dissolves.
Mechanisms of Action:
  • Peptide hormone binds cell membrane surface receptor and the hormone-receptor complex activates second messenger systems to initiate protein modification and synthesis.
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Hormone Synthesis

hormone synthesis, transport, binding, and effects.
Three classes of hormones:
    • Peptides and proteins (P&P)
    • Steroids (S)
    • Amines (A)
– Catecholamines (C) – Thyroid hormones (T)
4 hormone physiology features:
Synthesis
  • Hormones can be made in advance and stored prior to secretion.
– The peptide and protein hormones, and amines follow this model.
  • Alternatively, they can be synthesized and secreted on demand.
– The steroids follow this model.
Transport
  • This generally depends on chemical structure.
  • Hormones can either:
– Dissolve and travel freely in the blood – the peptides and proteins and also the catecholamines: they are water soluble (aka, hydrophilic) – Bind carrier proteins – the steroid and thyroid hormones are less water soluble and travel bound to carrier proteins.
Receptor binding
  • The chemical relationship between hormones and target cell membranes determines whether hormones:
– Bind surface membrane receptors – the peptide and protein hormones and the catecholamines, and in some cases, steroid hormones where they have non-genomic effects on the cell. – Bind intracellular receptors -- because they are lipophilic (lipid soluble), steroid hormones and thyroid hormones readily slip past the cell membrane to bind with cytoplasmic and/or nuclear receptors.
Mechanism of Action
  • Hormones can modify existing proteins within a cell – the peptide and protein hormones and the catecholamines.
  • Or they can trigger protein synthesis – the peptide and protein hormones do this, as well, as do the steroid and thyroid hormones.

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