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Difference between smooth and rough endoplasmic reticulum lies in the presence or absence of ribosomes on the surface. The endoplasmic reticulum falls under the endomembrane system along with the Golgi complex, lysosomes and vacuoles. They are networks or reticulums of tiny tubular structures scattered in the cytoplasm of the eukaryotes
Key terms: Endoplasmic Reticulum, rough endoplasmic reticulum, smooth endoplasmic reticulum, endoplasmic reticulum structure
Read Also: Nuclear Membrane
What is Endoplasmic Reticulum?
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The endoplasmic reticulum falls under the endomembrane system along with the Golgi complex, lysosomes and vacuoles. They are networks or reticulums of tiny tubular structures scattered in the cytoplasm of the eukaryotes. These structures are in charge of producing and transporting proteins, lipids, and other important chemicals for a cell's proper functioning.
Ribosomes are typically seen adhering to the outer surface of the Endoplasmic Reticulum. Rough endoplasmic reticulum is an endoplasmic reticulum that has ribosomes on its surface (RER), and Smooth endoplasmic reticulum is an endoplasmic reticulum that doesn’t have ribosomes on its surface (SER).
Structure of Endoplasmic Reticulum
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The nuclear envelope and the peripherals, which contains smooth tubules and rough sheets, make up the Endoplasmic Reticulum (ER). Despite the fact that the ER is characterized as an integrated network with a continuous membrane, the various structures that make up the ER conduct a wide range of specific activities within the cell.
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| Related Topics | ||
|---|---|---|
| What is Tissue? | Protoplasm | Cell Biology |
| Discovery of Cells | Transportation in Animals and Plants | Energy Currency of the Cell |
Rough Endoplasmic Reticulum (RER)
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The structure of the Rough Endoplasmic Reticulum (RER) forms a network of connected flattened sacs with many ribosomes on their outer surface. The membranes of RER contain a very vital protein, the translocon, which is necessary for protein translation within the rough ER.
Function of RER
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- The majority of RER’s actions are related to protein synthesis and protein folding.
- Protein sorting is the third most critical activity after protein synthesis and folding.
- Many proteins produced in the RER are packed and transferred to the Golgi apparatus in vesicles.
- Proteins may undergo minor changes in the RER lumen, such as having their signal sequences cleaved or being glycosylated.
Read Also: Proteins
Smooth Endoplasmic Reticulum (SER)
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The Smooth Endoplasmic Reticulum (SER) is a part of a continuing membrane organelle within the cytoplasm of eukaryotic cells, this meshwork of fine disc-like tubular membrane vesicles is involved in the synthesis and storage of lipids, including cholesterol and phospholipids, which are employed in the formation of new cellular membranes. The Structure of SER is of a tubular form.
Functions of SER
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- Smooth Endoplasmic Reticulum (SER) are in charge of producing important lipids like phospholipids and cholesterol, steroid hormone synthesis and secretion, glucose metabolism, and are beneficial to the neurological and muscular systems as they store and release calcium ions.
- The SER's function varies based on the cell type. It plays a critical part in the manufacture of steroid hormones from cholesterol in some cells, including those of the adrenal gland and other endocrine glands.
- The SER enzymes in the liver catalyze reactions that make medicines, metabolic wastes, and toxic substances water-soluble, allowing them to be removed from the body during detoxification.
- Glycogen-6-phosphatase, an enzyme found in SER, catalyzes the final step in glucose synthesis in the liver.
Read Also: Excretion in Plants
Difference Between RER and SER
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The difference between smooth and rough endoplasmic reticulum is tabulated below.
| Parameters | RER | SER |
|---|---|---|
| Attachment | Ribosomes attached to the endoplasmic reticulum | No ribosomes attached to the endoplasmic reticulum |
| Structure | Presence of cisternae and tubules | Presence of vesicles and tubules |
| Function | Play a vital role in enzymes and protein synthesis | Plays a vital role in glycogen, lipid and steroid synthesis. |
| Location | Generally connected to the nuclear envelope to the interior. The RER is also located near the Golgi apparatus. | Generally connected to plasmalemma, found on the peripheral region. The sarcoplasmic reticulum is a specific membrane structure that contains SER. |
| Ribophorins | Ribophorins are present on the surface for ribosomal attachment | Absence of ribophorins |
| Originated | They are evolved from the nuclear envelope | They are evolved from the rough ER, with the absence of ribosomes. |
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Things to Remember
- RER is found in a lot of cells that are involved in protein synthesis and secretion. They are long and contiguous with the nucleus's outer membrane.
- SER produces lipid-like steroidal hormones in animal cells. The main site for lipid synthesis is the smooth endoplasmic reticulum.
- SER aids in the production of new membranes as well as carbohydrate metabolism. It produces the enzyme glucose-6-phosphate in liver cells.
- In humans, abnormalities in RER structure and function are linked to a variety of diseases.
- In RER, the ribosomes are not attached whereas in SER, Ribosomes are attached to the surface.
Previous Year Questions
- Cisternae have a diameter of...[JKCET 2014]
- Cells divide and new cells are formed from pre-existing cells. This concept was given by..[AMUEEE 2010]
- Aleuroplasts in a cell stores...[AMUEEE 2010]
- Axoneme having 9 + 2 doublet microtubule arrangement is found in...[AMUEEE 2009]
- One of the chief functions of smooth endoplasmic reticulum is..[AMUEEE 2009]
- Cilia are :...[JKCET 2004]
- Which is not properly paired?..[JKCET 2004]
- What is true about fluid mosaic model?...[JKCET 2004]
- Besides proteins ribosomes contain :...[JKCET 2004]
- The movement of cilia and flagella is due to the presence of...[JKCET 2013]
- Plasma membrane helps in :...[JKCET 2005]
- Which of the following structure is bounded by single membrane?...[JKCET 2005]
- 70 S ribosomes occur in….[AMUEEE 2014]
- Rough endoplasmic reticulum is actively involved in...[JKCET 2014]
- Perinuclear space is present in...[JKCET 2014]
- Chloroplast lacks….[COMEDK UGET 2005]
- Colour of flower petals is due to...[CUCET 2012]
- Streaming of the cytoplasms within some living cell is known as...[CUCET 2011]
- Example of an oxidative organelle is...[CUCET 2011]
- Lampbrush chromosomes are...[COMEDK UGET 2005]
Sample Questions
Ques. What is called microsome? (2 marks)
Ans. Microsomes are small vesicles generated by the fragmentation of the ER membrane. Rough microsomes are those that are derived from RER, while smooth microsomes are those that do not contain ribosomes.
Ques. What is glycosylation? (2 marks)
Ans. The process of attaching sugar molecules to the nitrogen atom in an amino acid residue of a protein is known as glycosylation.
Ques. Differentiate between rough and smooth endoplasmic reticulum. How is the endoplasmic reticulum important for membrane biogenesis? (2 marks)
Ans. Differences between the rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER) are as follows :
| RER | SER |
|---|---|
| RER has ribosomes attached to its surface. | SER does not have ribosomes attached to its surface. |
| RER takes part in protein synthesis. | SER takes part in the synthesis of lipids and fats. |
Ques. What are the organelles in the endomembrane system? (2 marks)
Ans. The endomembrane system has 4 organelles:
- Endoplasmic reticulum
- Golgi apparatus
- Lysosomes
- Vacuoles
Ques. What steps does SER take to produce lipids? (2 marks)
Ans. Enzymes located in the SER's membrane produce lipids. This is because they have hydrophobic portions (affinity to particle) and the hydrophilic regions (affinity to water) of the fats, on the other hand, protrude into the cisternal area. When the lipid products are produced, they are bundled into vesicles and dispatched to their final destinations.
Ques. What is endocytosis? (2 marks)
Ans. The cell membranes flexibility allows the cell to engulf food and other material from its external environment. This process is known as endocytosis. E.g., Amoeba acquires its food through such processes.
Ques. Why are lysosomes called suicidal bags? (2 marks)
Ans. Lysosomes contain digestive enzymes and help in the cleaning of cells by digesting any foreign materials entering the cell, such as bacteria, food and old cell organelles.
When the lysosomes burst, the digestive enzyme digests its own cell. Hence it is called a suicidal bag.
Ques. What is the function of the nucleus in a cell? (2 marks)
Ans. The nucleus plays a very important role in the reproduction of cells. It also helps the single cell to divide and form two new daughter cells.
It plays an important role in determining how the cell will develop and what form it will exhibit at maturity, by directing the chemical activities of the cell.
Ques. Explain the structure and function of Golgi bodies. (3 marks)
Ans. Structures: Golgi bodies consist of a system of membrane-bound vesicles arranged in stacks parallel to each other called cisterns. These membranes have connections with the membrane of the endoplasmic reticulum (ER).
Functions:
(1) The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus.
(2) It also stores, modifies and helps in the packaging of products in vesicles.
(3) In some cases, complex sugars may be made from simple sugars in them.
(4) It also helps in the formation of lysosomes.
Ques. What are ribosomes? Where are they located in the cell? What is their function? (2 marks)
Ans. Ribosomes are spherical organelles present in the cell which are either freely distributed in the cytoplasm or may be attached to the endoplasmic reticulum.
It consists of ribosomal RNA (Ribonucleic acid) and proteins.
Functions of Ribosomes: It helps in the synthesis of proteins.
Ques. Why do plant cells have more in number and big-sized vacuoles as compared to animal cells? (2 marks)
Ans. Plant cells attain turgidity and rigidity due to the more number of vacuoles, as well as large-sized vacuoles, help the plant cells to withstand the wear and tear, external environmental conditions.
They also help in the storage of essential material required by plants for their growth like amino acids, sugar and various organic substances.
Ques. Explain the following terms: (3 marks)
(b) Cytoplasm
(c) Nucleus.
Ans. (a) Plasma membrane: It is a thin membrane which controls the passage of materials in and out of the cell. It is also called a selectively permeable membrane. It makes the outer boundary of the cell and is made up of lipo-protein,
(b) Cytoplasm: It is a transparent jelly-like thick substance present in the cell. It makes the ground of the cell in which all the cell organelles are suspended.
(c) Nucleus: It is a double-layered membrane structure which contains chromosomes required for the inheritance of characteristics from one generation to the other.
Ques. Do you agree “A cell is a building unit of an organism”? If yes, explain why. (2 marks)
Ans. An organism is made up of various organ systems like the digestive system, nervous system, etc. These organ systems in turn are made up of various organs which are made up of tissues. Also, tissues are a group of cells performing the same function. Hence, a cell is the building unit of an organism.
Cell → tissue → organ → organ system → organism
Ques. How will the absence of any one of the cell organelle affect the cell’s working? (2 marks)
Ans. Functions of all the organelles are inter-linked to each other and ultimately to the working of the cell. So, if even a single link is missing, the cell ultimately suffers and die. For example, DNA from the nucleus passes the information for protein formation to the ribosomes which send the proteins to Golgi complex and ER for modification and transport.
Ques. What is cell division? Give the types of cell division. (2 marks)
Ans. Cell division is a process of the formation of two or more daughter cells of their own type from the mother cell. These are similar in structure and function.
Cell division occurs in three ways:
- Amitosis
- Mitosis
- Meiosis
In each case, the division of the nucleus (Karyokinesis) occurs before the division of the cytoplasm (Cytokinesis).
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