Peptide Hormones: Definition, Types, and Examples

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Peptide Hormones Definition

Peptide hormones are a type of protein that binds to receptor proteins and either activates or inhibits a biological process. Hormones are biological substances that direct and coordinate development, growth, and reproduction in multicellular organisms. Peptide bonds between amino acids are referred to as peptide bonds. As a result, a peptide hormone is a chain of amino acids that functions as a biological communication molecule.

What are Peptide Hormones?

Peptide hormones have a short half-life, which means they disintegrate rapidly. This enables organisms to employ peptide hormones to guide processes rapidly and effectively, without the signal lingering for an extended period of time. As a result, peptide hormones are excellent candidates for intracellular hormones.

Many peptide hormones, on the other hand, are found in extracellular applications. Insects, all vertebrates, and a variety of other animals produce peptide hormones. Other hormones, like steroid hormones, must be broken down and expelled via urine or feces.

Synthesis of Peptide Hormones

Peptide hormones, like other proteins, are encoded in DNA, translated into a protein, and then changed or altered as needed. The endoplasmic reticulum is where the majority of protein synthesis takes place. Ribosomes are large protein complexes that read messenger RNA and transform it into an amino acid sequence.

Peptide hormones come in a variety of sizes, ranging from a few amino acids to several hundred. Peptide hormones are secreted by cells in one of two ways. The first, known as controlled secretion, produces a large amount of the hormone and stores it in a secretory granule or vesicle.

The granule bursts when a signal to release the hormone is delivered, and the hormone is released into the cell, out of the cell, or into the environment. Constitutive secretion is used to release other peptide hormones. Something tells the DNA to begin making the peptide hormone in this kind of hormone release.

A regulator protein may be deleted, or a growth factor could signal nucleus enzymes to make peptide hormones. They are produced and released at the same time, without being stored previously. When the signal is no longer there, the DNA is protected once again, and the organism ceases to produce peptide hormones.

Peptide Hormones Examples

i. Insulin

One of the most well-known peptide hormones is insulin. Insulin is a peptide hormone present in animals that aids in the regulation of glucose levels in cells and the circulation. Insulin works on all cells in the body, attaching to receptor proteins on the cell surface and allowing glucose to be absorbed.

Most significantly, insulin is self-regulating in healthy people because it is released in response to a high blood glucose level. This illustration depicts a cell in the pancreas, the organ that secretes insulin. The GLUT2 receptor, found on the surface of specialized islet beta cells of the pancreas, is responsible for glucose absorption.

This protein carries glucose into the cell, where it is converted to energy through the glycolysis process. It reaches the mitochondria after being broken down into smaller pieces, where it proceeds through the Krebs cycle and finally oxidative phosphorylation to create ATP.

The ATP-sensitive potassium channel shuts in response to an increase in ATP concentration. The potassium ions can no longer exit the cell as a result of this. When the potassium channel closes, ions on both sides of the membrane build up an electrical potential that is entirely disturbed. This causes the membrane to depolarize, similar to a nerve response.

The depolarization proceeds through the membrane until it reaches calcium channels that are activated by voltage. These channels open as a result of depolarization, allowing calcium ions to flood the cell. These calcium ions trigger the insulin-carrying secretory vesicles.

These tiny sacs attach to the plasma membrane and release pre-made peptide hormones into the circulation. They can circulate and signal cells to take up glucose there. When the concentration drops, the amount of ATP produced by the islet beta-cell decreases, and the system resets.

Insulin is a peptide hormone that is secreted in a controlled manner. Insulin was transcribed from DNA and processed by ribosomes long before the signal was received. Insulin is a 51-amino-acid peptide hormone, making it one of the lengthier peptide hormones.

After passing via the endoplasmic reticulum and the Golgi apparatus, the peptide hormone is packaged in secretory vesicles. This design allows a large amount of insulin to be released in a short period of time when it is needed.

ii. Other Human Peptide Hormones

Aside from insulin, the human body is dependent on a variety of other peptide hormones. Prolactin, a hormone that affects the mammary glands, and growth hormone, which regulates many aspects of growth and development, are two of these hormones. These hormones, like insulin, must be released at the right moment and under the direction of the DNA. This guarantees that the organism grows in a healthy manner.

Peptide Hormones in Other Organism

Peptide hormones are found in almost every living thing. While plant hormones have traditionally been limited to five types, scientists have recently verified the presence of peptide hormones in plants. Peptide hormones are used by every species on the planet. This is most likely owing to the relative simplicity with which peptide hormone pathways might be evolved.

Other hormones, which require totally new pathways to develop, will very certainly necessitate additional mutations and steady evolution. Peptide hormones might be generated by new DNA interactions, which are already a result of mutations.

Peptide Hormones Citations
  • Role of peptide hormones in insect gut physiology. Curr Opin Insect Sci . 2020 Oct;41:71-78.
  • The Roles of Peptide Hormones and Their Receptors during Plant Root Development. Genes (Basel) . 2020 Dec 25;12(1):22. 
  • Sulfated plant peptide hormones. J Exp Bot . 2019 Aug 19;70(16):4267-4277.
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