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/