hormone biosynthesis and secretion
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Hormone Biosynthesis & Secretion
Hormone synthesis
Hormone Type Characteristics Morphology
Peptides and proteins
Water soluble;made from large precursor molecules - prohormones.
secretory granules, RER
Steroids and iodinated tyrosines
Lipid soluble;made from low molecular weight precursors
lipid droplets
Protein/peptide secreting cell Steroid secreting cells
Hormone synthesis
Peptide hormone synthesis -Gene transcription
Processing of the initial mRNA transcript to ‘mature’ mRNA•excision of introns – and •modifications of the 3’ and 5’ ends
Translation of mRNA•Bound to the polyribosomes of RER, •the mRNA acts as a template for assembling amino acids by way of tRNA
Post translation processing •Cleavage of large pro-hormone•can also include folding of polypeptide chain and addition of carbohydrates (glycosylation)
Packaging of HormonesSignal sequence docking protein on
RER
As amino acids are assembled they are internalized into the RER
RER Golgi apparatus
Formation of secretory granules storage
Secretion by exocytosis
Membrane traffic in hormone-secreting cells
See the figure to understand how
hormone is secreted from the
endoplasmic reticulum (ER) and is then processed and
packaged in the Golgi Apparatus (see the various stages is
the packaging in Golgi) and finally exocytosis of the
hormone out of the cell.
Synthesis of insulinRNA
mRNA tRNA (preproinsulin)
Rough ER (signal sequence is removed and forms proinsulin)
A + B chains (Active insulin) in Golgi Apparatus
Secretory Granules
Homologous families of hormones
Homologous glycoprotein hormones (LH(hCG), FSH, TSH)
α and β sub-units. • α unit is common, • β unit determines
the biological activity
Ancestral gene
gonadotrophin
LH (hCG)
FSH
TSH
Steroid synthesis
Steroid hormone synthesis
• Cholesterol bound to sterol transfer protein - transported to mitochondria
• StAR protein transports cholesterol to inner mitochondrial membrane
• Cholesterol to pregnenolone by side chain cleavage enzyme, P450scc
• Between mitochondria and SER steroids synthesised by hydroxylase enzymes
Steroid Synthesis Simplified
Cholesterol
Pregnenolone
Progesterone
Aldosterone
17αOH Progesterone
Cortisol
Androgens
Oestrogens
Steroids are highly conserved
Outline of steroid synthesis in the adrenal
cortex and gonads
Synthesis of thyroid hormones Active uptake of iodine
into follicular cell
Oxidation of iodide to iodine
Iodination of tyrosine residues of thyroglobulin and apical-colloid interface
Storage in colloid
Uptake of thyroglobulin droplets into follicle cell
Release and secretion of T3 and T4
Peripheral conversion of thyroid and steroid hormones
T4 T3
Testosterone dihydrotestosterone
Testosterone oestradiol
Vitamin D (synthesised in skin) dihydroxy vitamin D.
Transport of steroid and thyroid hormones
An equilibrium exists between bound and free hormone.
e.g. transcortin, sex hormone binding globulin, transthyretin
PrepGenie thanks http://www.addison.ac.uk/