Difference Between Steroid and Peptide Hormones

Main Difference – Steroid vs Peptide Hormones

The main difference between steroid hormones and peptide hormones is that steroid hormones bind to the receptors inside the cytoplasm to act as second messengers, modifying the transcription, whereas peptide hormones mainly bind to the cell surface receptors the DNA in the nucleus.

Steroid and peptide hormones are two types of hormones in the animal body. In general, hormones are a type of signaling molecules that are produced by the endocrine glands, and they are transported throughout the body with the aid of the circulatory system. Also, the hormones regulate the physiology and behavior of the distant organs. Besides, the cholesterol  make up the steroid hormones, while the amino acids make up the peptide hormones. Testosterone and estrogen are examples of steroid hormones and antidiuretic hormone (ADH) and calcitonin are examples of peptide hormones.

Key Areas Covered

1. What are Steroid Hormones
      – Definition, Mechanism of Action, Function
2. What are Peptide Hormones
      – Definition, Mechanism of Action, Function
3. What are the Similarities Between Steroid and Peptide Hormones
      – Outline of Common Features
4. What is the Difference Between Steroid and Peptide Hormones
      – Comparison of Key Differences

Key Terms: Chromatin, Endocrine Glands, Endoplasmic reticulum (ER), Lipid Bilayer, Peptide Hormones, Second Messengers, Signaling Cascade, Steroid Hormones, Transcription Regulator

What are Steroid Hormones

Steroid hormones are secretions of ductless glands that consist of a characteristic steroid ring structure. Besides, they form from cholesterol. Sex hormones produced in the sex organs (testosterone, estrogen and progesterone), and hormones produced in the adrenal gland (aldosterone, cortisol, and androgens) are examples of steroid hormones.

Figure 1: Steroid Hormone Mechanism of Action

Moreover, the synthesis of steroid hormones occurs in the smooth endoplasmic reticulum when needed. Since steroid hormones are small hydrophobic molecules, they can freely diffuse through the lipid bilayer of the plasma membrane. Besides, they bind to a specific receptor inside the cytoplasm, and this receptor-bound steroid hormone complex is transported into the nucleus. Then, this receptor-bound steroid hormone complex binds to specific regions on the chromatin. So, this binding either activates or releases the associated proteins of chromatin to modify the transcription. In the end, the steroid hormone determines the amount of a particular protein in the cell. Thereby, the receptor-bound steroid hormone complex acts as a transcription regulator. The figure 1 shows the mechanism of action of the steroid hormone.

Furthermore, the anabolic steroid hormones are male sex hormone-related, synthetic steroids. They stimulate the protein synthesis in the body to increase the muscle mass. 

What are Peptide Hormones

Peptide hormones refer to any hormone derived from amino acids. They can be either small or large hydrophilic molecules synthesized in the rough endoplasmic reticulum. The vesicles store peptide hormones until it receives the signals for the secretion. Since they are hydrophilic molecules, peptide hormones are unable to freely diffuse through the lipid bilayer. Therefore, the receptors for the peptide hormones are located on the surface of the target cell. Also, these receptors are made up of a single polypeptide chain, which comprises domains on either side of the plasma membrane. Furthermore, these intracellular and extracellular domains are connected by a membrane-spanning domain.

Figure 2: Peptide Hormones

Moreover, multiple polypeptides make up some of the receptors. The peptide hormones are the first messengers of the signaling pathway. The binding of the peptide hormone to the receptor activates the G-protein, which is located in the membrane. Further, the activated G-protein stimulates enzymes such as adenyl cyclase and phospholipase C in the plasma membrane, producing second messengers such as cyclic AMP (cAMP). Then, those second messengers bind to the protein kinase A. Finally, the activated protein kinase A phosphorylates other proteins, initiating a signal cascade to modify various functions of the cell.

Similarities Between Steroid and Peptide Hormones

• Both steroid and peptide hormones are signaling molecules that regulate the physiology and the behavior of organs.
• Also, both hormones are produced in the endocrine glands and released into the bloodstream in order to be transported to the target organ.
• Typically, both exert a prolonged action.

Difference Between Steroid and Peptide Hormones

Definition

Steroid Hormones: Steroid hormones refer to secretions of the ductless glands, which consist of the characteristic steroid ring structure and are formed from cholesterol.

Peptide Hormones: Peptide hormones refer to any hormone derived from amino acids.

Composition

Steroid Hormones: Steroid hormones are made up of cholesterol.

Peptide Hormones: Peptide hormones are made up of amino acids.

Structure

Steroid Hormones: Steroid hormones are small hydrophobic molecules.

Peptide Hormones: Peptide hormones are large or small hydrophilic molecules.

Synthesized in

Steroid Hormones: Steroid hormones are synthesized in the smooth ER.

Peptide Hormones: Peptide hormones are synthesized in the rough ER.

Release

Steroid Hormones: Steroid hormones are synthesized when needed.

Peptide Hormones: Peptide hormones are stored until the signals are received for the secretion.

Transport in the Bloodstream

Steroid Hormones: Steroid hormones are stuck to the protein carriers in order to be transported through the bloodstream.

Peptide Hormones: Peptide hormones are freely transported through the bloodstream.

Location of the Receptor

Steroid Hormones: The receptors of the steroid hormones occur on the cell surface.

Peptide Hormones: The receptors of the peptide hormones occur inside the nucleus.

Mechanism of Action

Steroid Hormones: Steroid hormones serve as second messengers.

Peptide Hormones: Peptide hormones bind to DNA to modify the transcription.

Speed of the Effect

Steroid Hormones: Steroid hormones consist of a slower action.

Peptide Hormones: Peptide hormones consist of a rapid action.

Longevity of the Effect

Steroid Hormones: Steroid hormones exert a permanent action.

Peptide Hormones: Peptide hormones exert a temporary action.

Examples

Steroid Hormones: Testosterone and estrogen are examples of steroid hormones.

Peptide Hormones: Antidiuretic hormone (ADH) and calcitonin are examples of peptide hormones.

Conclusion

Steroid hormones and peptide hormones are two types of hormones in the animal body that serve as signaling molecules. Steroid hormones are made up of cholesterol while peptide hormones are made up of amino acids. Since steroid hormones are hydrophobic molecules, they freely diffuse through the lipid bilayer. Therefore, the receptors of the steroid hormones are located inside the cell. However, peptide hormones are hydrophilic molecules, and cannot diffuse through the lipid bilayer. Their receptors are located on the plasma membrane. They initiate signaling cascades through the second messengers. Therefore, the main difference between steroid and peptide hormones is their location of the receptors and the mechanism of action.

Reference:

1.Bailey, Regina. “How Do Steroid Hormones Work?” ThoughtCo, Available here. Accessed 2 Oct. 2017.
2.Peptide Hormones. The Medical Biochemistry Page. Available here. Accessed 2 Oct. 2017.

Image Courtesy:

1. “Endocytosis of Steroid Hormones” By Mcfall2016 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “1804 Binding of Water-Soluble Hormones” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia

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