The endoplasmic reticulum (ER) is an organelle present in eukaryotic cells. There are two types of endoplasmic reticulum, namely, rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). These two organelles have similar structures but are very different from each other.
To help you identify and understand the difference, I have put together this detailed comparison of rough vs smooth ER.
From your early knowledge of living cells, you will remember that circular structures or dots were used to differentiate the two endoplasmic reticula.
Yes, those structures and many other features are what sets one endoplasmic reticulum apart from the other. You will learn about this in the article.
The endoplasmic reticulum
The ER is a continuous membrane system (from the nuclear membrane) that appears like flattened sacs in the cytoplasm of eukaryotes. It takes up about 10% of the total cell volume and is responsible for the metabolism and transportation of carbohydrates, proteins, and lipids to other organelles.
The ER is made of the RER and SER subunits that carry out specialized functions, still in tandem with the general function of the ER. The ER is made up of cavities and the lumen, the internal space. These organelles are important to the synthesis of lipids, glycogen, steroids, and proteins.
It provides a wide area for diverse cellular reactions, acts as a support framework, and helps to maintain cellular structure.
Similarities: Rough vs smooth ER
Here are some similarities between the RER and SER:
- Both types of ER are membrane-bound organelles with a phospholipid bilayer membrane
- They are interconnected with the nuclear membrane of the cell, which makes the exchange of and transportation of molecules within the cell
- Both organelles are responsible for homeostasis in eukaryotes
- Although the primary assignment of the RER is protein synthesis, it also participates in lipid synthesis (though limited in functions)
- They have dynamic structures and can quickly adapt to changing cellular demands. The distribution of RER and SER can change with the changing needs of the cell
- In addition, both structures of ER depend on the cytoskeletal framework of the cell
Differences: Rough vs smooth ER
Let’s look at the differences:
Structure
The RER are flattened sacs studded with ribosomes on the outer region. The ribosomes attach themselves to the ER using proteins called ribophorins. The flattened sacs are called the cisternae. They also contain a protein complex called the transcolon.
On the other hand, the SER have a smooth surface and are usually produced from the RER after they have shed off their ribosomes. They are made of vesicles and tubules.
The structure and appearance of the RER tend to be more complex than that of the SER because of the ribosomes. Sometimes, some of the ribosomes detach from the RER and develop into separate cisternae.
Localization
The two types of ER are present in all plant and animal cells but are different in localization. Localization of ER varies with the function and type of cell.
The SER is found near the cell membrane, while the RER is found near the cytoplasm, and very close to the Golgi apparatus.
RER is abundant in cells that specialize in protein secretion and gland cells, such as goblet cells, pancreatic cells, Nissi’s granules of the nerve cells, and plasma cells that specialize in producing antibodies.
The SER is abundant in cells that produce steroids and carry out lipid metabolism. Some of these cells are present in the liver, adipocytes, interstitial cells of the testes, muscle cells, leukocytes, and the adrenal cortex cells.
Functions
The major function of the RER is the production, modification, and transportation of proteins. The SER is majorly responsible for the production of lipids and the storage of calcium ions. The RER contains enzymes that catalyze protein synthesis from RNA.
Also, the RER oversees quality control during the folding of proteins. It ensures that only the correctly folded proteins leave the ER to their respective locations. The misfolded proteins remain in the RER for refolding or elimination.
The function of the SER varies with its localization. In the endocrine system, it uses cholesterol to produce steroid hormones. In the liver, it is responsible for detoxification. It produces enzymes that stimulate the removal of drugs, metabolic wastes, and other toxins from the body.
Furthermore, the RER provides the Golgi apparatus, plant vacuoles, endosomes, and lysosomes with protein and lipids, while the SER provides the vesicles for the cis face of the Golgi apparatus.
In addition, the RER plays an important role in the formation of lysosomes, and the SER is involved in the formation of spherosomes and oleosomes.
What type of proteins are synthesized by the rough endoplasmic reticulum?
The ribosomes on the RER carry out the synthesis of the transmembrane and water-soluble proteins. Transmembrane proteins are lodged in the RER, and the water-soluble proteins enter the lumen of the RER via the transcolon channel.
Furthermore, the transmembrane proteins carry out special functions in the ER and other cellular organelles. Water-soluble proteins exercise their functions in the lumen of cellular organelles and are responsible for secretion.
Do rough and smooth endoplasmic reticulum work together?
Yes, they do. As mentioned earlier, the RER and SER sub-compartments of one organelle. They may carry out different functions, but they are in synergy to ensure the overall health and functionality of the cell.
Under certain conditions, the proteins produced in the RER may enter the SER for lipid attachment. The lipids synthesized in the SER may also enter the RER for different modifications of proteins.
FAQs
What type of ribosomes are present in the rough ER of eukaryotes?
The ribosomes on the RER are called membrane-bound. The second stage of gene expression – translation – occurs in these ribosomes. Afterward, the protein goes back into the RER for processing.
What are the diseases of the endoplasmic reticulum?
Dysfunction in the endoplasmic reticula could be from the rough or smooth endoplasmic reticulum. Dysfunction of the RER could lead to protein misfolding disorders. Misfolded proteins disrupt cellular processes, which could be the onset of Alzheimer’s disease.
Also, a dysfunction of the SER could cause lipid-related disorders and interruptions of the detoxification process. Most liver diseases are a result of SER dysfunction.
Is the distribution of rough Vs smooth ER the same in all cells?
The distribution of RER and SER in cells depends on the primary function of the cell. Cells that carry out a lot of protein synthesis will have more RER than SER. Similarly, cells that specialize in lipid metabolism will have more SER.
However, under certain conditions, the cells can adjust the RER and SER ratio to suit cellular needs. That is, if a cell experiences increased protein synthesis, it will readjust and enhance the function of the SER than the RER.
Conclusion
All cellular organelles are unique in their way and contribute to the overall health and functionality of the cell. The comparison of the rough vs smooth endoplasmic reticulum is not to weigh the superiority of one over the other. It shows the division of labor in living cells.
The rough endoplasmic reticulum is responsible for the synthesis of proteins, while the smooth endoplasmic reticulum carries out lipid metabolism and detoxification.
Among their differences are also some similarities that show an interconnection and cellular specialization.
Here is another comparison of seemingly similar cel components, chloroplast vs chlorophyll.
Thanks for reading.