Protein hormones are synthesized through a carefully orchestrated process that often involves precursor molecules. These precursor forms ensure proper folding and trafficking before the active hormone is released.
The Synthesis Process
The synthesis of protein hormones typically follows these key steps:
- Transcription: The process begins in the cell nucleus, where the DNA code for the hormone is transcribed into messenger RNA (mRNA).
- Translation: The mRNA then moves to the ribosomes in the cytoplasm. Here, the genetic code on the mRNA is translated into an amino acid sequence, creating a polypeptide chain called a preprohormone.
- Modification in the Endoplasmic Reticulum (ER): The preprohormone enters the ER where the signal peptide is removed forming a prohormone. The prohormone undergoes folding and other modifications.
- Processing in the Golgi Apparatus: The prohormone then moves to the Golgi apparatus, where it is further processed. This can involve glycosylation, proteolytic cleavage, and other modifications.
- Proteolytic Cleavage: Many protein hormones are synthesized as prohormones, then proteolytically clipped to generate their mature form. In some cases, the prohormone or a larger precursor protein will undergo multiple proteolytic cleavages to release the final, active hormone. This precise cleavage is essential for activating the hormone.
- Packaging and Release: Finally, the mature hormone is packaged into secretory vesicles and released from the cell via exocytosis.
Types of Protein Hormone Synthesis
Protein hormone synthesis is often a multi-step process that can be categorized based on the modification of the precursor molecules:
- Prohormone Processing:
- Many protein hormones are initially made as larger, inactive prohormones.
- These prohormones require proteolytic cleavage to become the active hormone.
- Example: Insulin is synthesized as proinsulin, which is then cleaved to produce the active insulin molecule.
- Precursor Protein Release:
- The hormone is originally a part of a larger precursor protein sequence.
- Multiple proteolytic cleavages are necessary to release the hormone from the precursor.
- This method allows for fine-tuned control over hormone release.
Summary
| Stage | Description |
|---|---|
| Preprohormone | Initial polypeptide chain, contains a signal peptide for ER entry. |
| Prohormone | Formed in the ER by removal of signal peptide; requires further processing. |
| Mature Hormone | Final, active form after proteolytic cleavage of the prohormone or precursor protein. |
In essence, protein hormone synthesis is a precise process that often requires the processing of precursor molecules like prohormones. This ensures hormones are produced and released in their proper active form at the right time and place.
