How Amino Acid-Based Hormones Are Made

Location: Occurs in the nucleus (the cell's command center).
Process: A specific gene on the $\text{DNA}$ is transcribed into messenger $\text{RNA}$ ( $\text{mRNA}$ ).
Modifications: To prevent enzymatic degradation in the cytosol, a $5'$ cap and a poly-A tail are added to the $\text{mRNA}$ before it exits through nuclear pores.

Translation: Occurs on ribosomes located on the rough endoplasmic reticulum ( $ext{ER}$ ). The $\text{mRNA}$ is translated into a sequence of amino acids forming a protein.

Folding: The rough $\text{ER}$ provides a protected environment for the protein to fold properly for export.
Transport and Modification: * The protein, initially a preprohormone (or prohormone), is packaged into transport vesicles and moved to the Golgi apparatus. * Within the Golgi cisterns, the hormone undergoes post-translational modification, which may involve snipping ends of the protein or adding carbohydrate tags. * The result is the finalized hormone, such as $\text{TRH}$ .

Storage Capability: Unlike steroid hormones, amino acid-based hormones stay within membrane-bound vesicles and may be stored inside the cell until a stimulus triggers their release.
Secretion: Vesicles fuse with the plasma membrane to release the hormone into the extracellular space/bloodstream.
Blood Transport: These hormones are water-soluble and do not require a protein carrier to travel through the blood.
Synthesis vs. Blood Levels: Because these hormones are stored, their concentration in the blood does not necessarily reflect the current rate of synthesis.
Target Example: $\text{TRH}$ is produced in the hypothalamus and travels via the blood to affect $\text{TSH}$ -producing cells in the anterior pituitary.