Key Roles of the Endoplasmic Reticulum and Golgi Body in Cells
The organelle, endoplasmic reticulum, which can be seen as present in almost all eukaryotic cells is an organelle that consists of two subunits – SER(smooth endoplasmic reticulum) and RER(rough endoplasmic reticulum). These organelles in rough endoplasmic reticulum form cisternae, a mesh of interconnected, flattened membrane-enclosed sacs, and SER exist as tubular structures. With an exterior nuclear membrane, endoplasmic membranes are continuous. However, these organelles are not present in spermatozoa or red blood cells.
Golgi apparatus was discovered by Camillo Golgi, in the year 1950. It is also called a Golgi Complex or Golgi body, the membrane-bound organelle of eukaryotic cells (cells with clearly defined nuclei) that is made up of a series of flattened, stacked pouches called cisternae. The Golgi apparatus functions to transport, modify, and pack proteins and lipids into vesicles for delivery to targeted destinations. It is placed in the cytoplasm next to the endoplasmic reticulum and near the cell nucleus. While many types of cells contain only one or several Golgi apparatus, plant cells can contain hundreds.
The Function of Golgi Apparatus
Golgi apparatus performs various important functions inside the cell like:
(i) The main function of the Golgi apparatus is to carry out the processing of proteins generated in the endoplasmic reticulum. Golgi apparatus also transports protein to the different parts of the cell.
(ii) The modification of cargo proteins is carried out by the Golgi enzymes present in membranous disks of cisternae. Modification of various substances is carried out by enzymes in cisternae with the help of processes like phosphorylation and glycosylation.
(iii) Nucleotide sugars are imported by the Golgi apparatus from the cytosol to carry out the glycosylation and phosphorylation processes.
(iv) Polysaccharides are attached with proteins in order to form care) One of the tasks of the Golgi apparatus is carrying out the breakdown of proteins and the formation of small, active fragments. carbohydrates.
(v) One of the tasks of the Golgi apparatus is carrying out the breakdown of proteins and formation of small, active fragments.
(vi) Sulfate groups are put to protein molecules in the Golgi apparatus.
(vii) Adding phosphate molecules onto molecules of proteins is also a vital task carried out in the Golgi apparatus.
(viii) Transfer of lipids around cells and creation of lysosomes are the vital functions carried out by the Golgi apparatus.
(ix) The Golgi body carries out the synthesis of proteoglycans. The proteoglycans are found in the extracellular matrices of animal cells.
(x) Carbohydrates are synthesized in the Golgi body. The process of carbohydrate synthesis involves the production of polysaccharides and glycosaminoglycans (GAGs).
MCQs
1. The Place where the process of Detoxification of Xenobiotic Compounds occurs
(a) Rough Endoplasmic Reticulum
(b) Ribosomes
(c) Cytosol
(d) Smooth Endoplasmic Reticulum
Answer: (d)
2. This is the function of Glycosylation
(a) Helps in cell-cell adhesion
(b) Confer stability in proteins
(c) Helps in the proper folding of the protein
(d) Synthesis of membrane lipid
Answer: (d)
3. This is a correctly matched pair
(a) Lysosomes – involved in synthesizing amino acids
(b) Microsomes – take part in photosynthesis
(c) Centrosomes – Provides enzymes essential for digestion
(d) Endoplasmic Reticulum – has a role in the formation of a new nuclear membrane while cell divides
Answer: (d)
4. The Endoplasmic Reticulum in fastly dividing cells is
(a) Absent
(b) Not functional
(c) Poorly developed
(d) Highly developed
Answer: (c)
5. The ER and bodies linked with it during ultracentrifugation are separated as a fraction known as
(a) Episome
(b) Polysome
(c) Microsome
(d) Quantasome
Answer: (c)
6. Sarcoplasmic Reticulum is associated with
(a) Hormone synthesis
(b) Protein synthesis
(c) Release of calcium ions from muscle contractions
(d) None of the above
Answer: (c)
7. This is related to the Glycosylation of protein
(a) Lysosome
(b) Peroxisome
(c) Mitochondria
(d) ER
Answer: (d)
8. The transfer vesicle from RER fuse with the region of Golgi complex
(a) Protein Arms
(b) Medial
(c) Cis
(d) Trans
Answer: (c)
9. SER produces
(a) Nucleic Acid
(b) Carbohydrate
(c) Protein
(d) Lipid
Answer: (d)
Endoplasmic Reticulum
The endoplasmic reticulum is a network of tubes inside a cell and is of two forms, One form has a surface decorated with round organelles called ribosomes which are used to prepare proteins, and is called coarse endoplasmic reticulum while the other has a smooth surface without ribosomes and is used to prepare other substances, is called the smooth endoplasmic reticulum. These membranes form continuous creases that eventually bind to the outer layer of the nuclear envelope. The endoplasmic reticulum is observed in all other eukaryotic cells, except for sperm cells and red blood cells.
The Function of Endoplasmic Reticulum
The function of Smooth endoplasmic reticulum:
The Smooth Endoplasmic Reticulum is responsible for the synthesis of essential lipids such as phospholipids and cholesterol which are necessary for the construction of cell membranes.
It helps to detoxify certain compounds
It helps in carbohydrate metabolism.
Helps in storing and releasing calcium ions, necessary in the contraction of muscle cells and synthesizing male and female hormones in the brain.
The Function of Coarse/Rough Endoplasmic Reticulum
Most of the functions of rough ER are related to protein synthesis because of the round organelles present on top.
Rough endoplasmic reticulum helps in protein folding and quality control.
The second most important function after protein synthesis and protein folding is protein selection.
Rough ER produces antibodies in specific white blood cells. In pancreatic cells, the coarse endoplasmic reticulum produces insulin.
Golgi Body
The Golgi apparatus or Golgi body named after Camillo Golgi is an organelle that looks like a series of stacked membranes and assists in the processing and packaging of proteins and lipid molecules, especially those intended for export from cells.
Some of them are renal tubules and some of them are vesicles. The Golgi is very close to the core. It is called the perinuclear body and is also near the endoplasmic reticulum. And as proteins emerge from the endoplasmic reticulum, they go to the Golgi for further processing.
The Function of Golgi Body
One of the functions of the Golgi is to create new vesicles from the existing Golgi membrane and inject these vesicles with glycoproteins and other substances produced by the Golgi network.
The Golgi complex serves as a “traffic police officer” for cells, responsible for directing proteins and lipids to the correct target.
They play a role in the exocytosis of a wide variety of products and proteins, including fragments of zymogen, mucus, lactoprotein, and thyroid hormone.
Other organelles, such as cell membranes and lysozyme, are synthesized by the Golgi complex.
It is also involved in the sulfation of various compounds.
Similarities between Endoplasmic Reticulum and Golgi Body
The endoplasmic reticulum and the Golgi apparatus are two membrane-bound organelles found in eukaryotes with similar functions. Both the endoplasmic reticulum (ER) and the Golgi apparatus are two components of the cell's endomembrane system. Lysosomes and vesicles are other components of the endomembrane system. There are two types of eukaryotic cells: coarse endoplasmic reticulum and smooth endoplasmic reticulum. The ribosome binds to the rough ER and transports the synthesized polypeptide chain to the rough ER. Post-translational modifications of proteins occur within the ER, thereby maturing the protein. These mature proteins are transported to the Golgi apparatus and transported to their final destination, either by lysosomes, plasma membranes, or excreted from cells into the extracellular environment. Secretion to the extracellular environment is caused by exocytosis.
FAQs on Endoplasmic Reticulum and Golgi Body Explained
1. What is the Endoplasmic Reticulum (ER) and where is it located in a cell?
The Endoplasmic Reticulum (ER) is a large, dynamic network of interconnected membranous tubes and flattened sacs called cisternae. It is found exclusively in eukaryotic cells and extends from the outer nuclear membrane into the cytoplasm. The ER plays a crucial role in protein and lipid synthesis and serves as an intracellular transport system.
2. What are the two types of Endoplasmic Reticulum, and what are their main functions?
The Endoplasmic Reticulum is divided into two distinct types based on its structure and function:
Rough Endoplasmic Reticulum (RER): Its surface is studded with ribosomes, giving it a 'rough' appearance. Its primary function is the synthesis, folding, and modification of proteins that are destined for secretion or for delivery to other organelles.
Smooth Endoplasmic Reticulum (SER): It lacks ribosomes, giving it a 'smooth' surface. The SER is vital for synthesising lipids and steroids, metabolising carbohydrates, and detoxifying drugs and poisons in the cell.
3. What is the Golgi Apparatus, also known as the Golgi Body?
The Golgi Apparatus, or Golgi Body, is a cell organelle composed of a series of flattened, stacked, membrane-bound sacs known as cisternae. It functions as the cell's primary 'post office' or packaging unit. It receives proteins and lipids from the Endoplasmic Reticulum, modifies, sorts, and packages them into vesicles for transport to other destinations within or outside the cell.
4. What is the primary difference between the structure of the Endoplasmic Reticulum and the Golgi Apparatus?
The main structural difference lies in their connectivity. The cisternae of the Endoplasmic Reticulum form a continuous, interconnected network of tubules and sacs throughout the cytoplasm. In contrast, the cisternae of the Golgi Apparatus are a stack of separate, unconnected compartments, each with a distinct 'cis' (receiving) face and 'trans' (shipping) face.
5. How do the Endoplasmic Reticulum and Golgi Apparatus work together as part of the endomembrane system?
The ER and Golgi Apparatus work in a coordinated sequence. First, the Rough ER synthesises proteins, which are then packaged into small transport vesicles. These vesicles bud off from the ER and travel to the 'cis' face of the Golgi Apparatus, where they fuse and release their contents. Inside the Golgi, these molecules are further processed, sorted, and packaged into new vesicles that bud off from the 'trans' face for their final destination, such as the cell membrane or lysosomes.
6. Why is the Rough ER studded with ribosomes while the Smooth ER is not?
This structural difference is directly related to their distinct functions. The Rough ER is primarily involved in synthesising proteins that will be exported from the cell or embedded in its membranes. Ribosomes are the cellular machinery for protein synthesis, so their attachment to the RER membrane allows newly made proteins to be directly channelled into the ER lumen for processing. The Smooth ER, on the other hand, deals with lipid synthesis and detoxification, processes that do not require ribosomes.
7. What would happen to a cell if its Golgi Apparatus was non-functional?
If the Golgi Apparatus stopped working, the cell's ability to sort and transport essential molecules would be severely compromised. Proteins and lipids synthesised in the ER would not be properly modified or dispatched to their correct locations. This would lead to a buildup of unprocessed materials, failure to secrete hormones or enzymes, inability to form new lysosomes, and disruption of the cell membrane, ultimately leading to cell death.
8. What is membrane biogenesis and how is the ER involved?
Membrane biogenesis is the process of building the cell membrane. The Endoplasmic Reticulum plays a central role in this process. The proteins and lipids required for the cell membrane are synthesised by the RER and SER, respectively. These components are then assembled into new sections of membrane, which can be incorporated into the ER itself or transported via vesicles to the Golgi Apparatus and then to the plasma membrane to help it grow and repair.
9. How is the structure of the Golgi Apparatus perfectly suited for its 'post office' function?
The Golgi's structure is highly specialised for its role. It has two distinct faces:
The cis face (forming face) is oriented towards the ER to receive transport vesicles containing raw proteins and lipids.
The trans face (maturing face) is oriented towards the cell membrane and is where the fully processed molecules are packaged into new vesicles for shipping.
This structural polarity ensures a one-way flow of materials, allowing for sequential modification and sorting as they pass through the different cisternae, much like an assembly line.
10. Do all eukaryotic cells have the same amount of ER and Golgi bodies?
No, the quantity of ER and Golgi bodies varies depending on the cell's primary function. For example, cells that are specialised for secreting large amounts of proteins, such as pancreatic cells that produce insulin or plasma cells that produce antibodies, have a very extensive Rough ER and a large, well-developed Golgi Apparatus to handle the high volume of protein synthesis, processing, and export.
