The main difference between constitutive and regulated secretion is that vesicles form continuously and carry proteins from the Golgi apparatus to the cell surface in constitutive secretion, whereas proteins are consolidated into vesicles and stored in the cell to secrete in response to a specific signal in regulated secretion.
Constitutive and regulated secretion are two secretory pathways that bring proteins from the Golgi apparatus to the cell surface. They are important for exporting proteins to the extracellular environment.
Key Areas Covered
1. What is Constitutive Secretion
– Definition, Process, Examples
2. What is Regulated Secretion
– Definition, Process, Examples
3. Similarities Between Constitutive and Regulated Secretion
– Outline of Common Features
4. Difference Between Constitutive and Regulated Secretion
– Comparison of Key Differences
Key Terms
Constitutive Secretion, Regulated Secretion
What is Constitutive Secretion
Constitutive secretion is a secretory pathway that continuously secretes proteins and other molecules to the cell exterior from the Golgi apparatus. The main feature of the constitutive secretion is the continuous stream of vesicles from the Golgi apparatus. It often occurs in cell membrane proteins, polysaccharides, and lipids. Glycoproteins are an example of a material that undergoes constitutive secretion. They are a major part of the extracellular matrix. Also, the trans-Golgi network is the key station that sorts proteins into distinct transport pathways. Proteins that undergo constitutive secretion do not aggregate in the trans-Golgi network.
Figure 1: Constitutive Secretion
Furthermore, constitutive secretion contains proteins destined for extracellular release. Also, they occur in exocytotic vesicles. They bud off after packaging and immediately move toward the plasma membrane. Then, they fuse into the plasma membrane and release the content into the extracellular space. The release of antibodies by activated plasma B cells is an example of constitutive secretion.
What is Regulated Secretion
Regulated secretion is another secretory pathway that forms secretory vesicles to regulate the secretion process. They also contain proteins destined for extracellular release. Importantly, the proteins that undergo regulated secretion aggregate in the trans-Golgi network. Then, they form dense core secretory granules. Significantly, they are stored in the cell until a signal is given for the release. With the receiver of the appropriate signal, they move towards the membrane and fuse into the plasma membrane to release the content. Neurotransmitter release from the neurons is an example of regulated secretion.
Figure 2: Regulated Secretion
Moreover, proteins in the regulate secretion are released on demand. For example, beta cells of the pancreas produce insulin stored in the dense core secretory granules. Insulin-containing dense core secretory granules fuse into the plasma membrane with increased blood sugar. The release of insulin into the blood reduces the levels of glucose. Also, the acinar cells of the pancreas store digestive enzymes in the dense core secretory granules called zymogen granules. Following feeding, they are released into the gut.
Similarities Between Constitutive and Regulated Secretion
- Constitutive and regulated secretion are two secretory pathways in the cell.
- They export proteins from the Golgi apparatus to the cell exterior.
Difference Between Constitutive and Regulated Secretion
Definition
Constitutive secretion refers to one of the pathways by which proteins are secreted continuously, regardless of external factors or signals. In contrast, regulated secretion refers to another pathway by which protein is sorted from the Golgi into storage/secretory granules (SGs) whose contents are released when stimuli trigger their final fusion with the plasma membrane.
Continuation
Vesicles form continuously and carry proteins from the Golgi apparatus to the cell surface in constitutive secretion, while proteins are consolidated into vesicles and stored in the cell in regulated secretion.
Formation of Secretory Vesicles
Constitutive secretion does not form secretory vesicles, while regulated secretion forms secretory vesicles.
Stimulus
Secretion occurs regardless of stimuli in constitutive secretion, while secretion occurs in response to stimuli in regulated secretion.
Aggregation in the Trans Golgi Network
Proteins destined for constitutive secretory pathways do not aggregate in the trans-Golgi network, while proteins destined for regulated secretory pathway aggregate in the trans-Golgi network.
Examples
Cell wall polysaccharides and glycoproteins are secreted in constitutive secretory pathways, while hormones such as insulin are secreted in regulated secretory pathways.
Conclusion
In brief, constitutive and regulated secretion are two secretory pathways that export proteins from the Golgi apparatus to the cell exterior. Constitutive secretion is continuous and does not form secretory vesicles. The secretion occurs regardless of the stimulus. Proteins in the constitutive secretion do not aggregate in the trans-Golgi apparatus. Cell wall polysaccharides and glycoproteins use the constitutive section. In comparison, regulated secretion is not a continuous process, and it forms secretory vesicles. Proteins that use it aggregate in the trans-Golgi network. Hormones such as insulin use regulated secretion. Therefore, the main difference between constitutive and regulated secretion is the continuation of the process.
References:
- Protein processing III: Secretion, lysosomal and endocytotic pathways. Secretion and Endocytosis. (n.d.).
Image Courtesy:
- “0314 Golgi Apparatus a en” By OpenStax – Own work (CC-BY 3.0) via Commons Wikimedia
- “Secretory mechanism” By Wonjinee – Own Work (CC-BY SA 4.0) via Commons Wikimedia
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