What are the structure and functions of endoplasmic reticulum and Golgi body
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 Structure and Roles in Cells
1. What is the endoplasmic reticulum?
The endoplasmic reticulum (ER) is a membrane-bound organelle in eukaryotic cells that synthesizes proteins and lipids and transports materials within the cell. It is a network of flattened sacs and tubules connected to the nuclear membrane.
- Rough ER (RER) has ribosomes attached and makes proteins.
- Smooth ER (SER) lacks ribosomes and synthesizes lipids and steroids.
- It helps in intracellular transport and membrane production.
2. What is the Golgi body and what does it do?
The Golgi body, also called the Golgi apparatus, is a cell organelle that modifies, packages, and distributes proteins and lipids received from the ER. It consists of stacked, flattened sacs called cisternae.
- Modifies proteins (e.g., glycosylation).
- Sorts and packages molecules into vesicles.
- Forms secretory vesicles and lysosomes.
3. What is the difference between rough ER and smooth ER?
The main difference between rough ER and smooth ER is that rough ER has ribosomes for protein synthesis, while smooth ER lacks ribosomes and synthesizes lipids.
- Rough ER: Protein synthesis and folding; appears rough due to ribosomes.
- Smooth ER: Lipid synthesis, detoxification, and calcium storage.
- Both are parts of the same endoplasmic reticulum network.
4. How does the endoplasmic reticulum work with the Golgi apparatus?
The endoplasmic reticulum and Golgi apparatus work together to synthesize, modify, and transport proteins and lipids. The process occurs in steps:
- Proteins are synthesized in the rough ER.
- Transport vesicles carry them to the Golgi body.
- The Golgi modifies, sorts, and packages them for secretion or cellular use.
5. What are the main functions of the Golgi apparatus?
The Golgi apparatus mainly modifies, sorts, and packages proteins and lipids for transport. Its key functions include:
- Chemical modification such as glycosylation.
- Packaging molecules into vesicles.
- Formation of lysosomes.
- Secretion of proteins outside the cell.
6. Where is the endoplasmic reticulum located in the cell?
The endoplasmic reticulum is located in the cytoplasm and is continuous with the outer membrane of the nuclear envelope. It extends throughout the cell as a network of membranes.
- Connected directly to the nucleus.
- Spreads across the cytoplasm.
- Closely associated with ribosomes (in rough ER).
7. What is the structure of the Golgi body?
The Golgi body is made up of stacked, flattened membrane sacs called cisternae with associated vesicles. It has three main regions:
- Cis face (receiving side from ER).
- Medial region (modification area).
- Trans face (shipping side to other destinations).
8. What is the role of smooth ER in cells?
The smooth endoplasmic reticulum (SER) is responsible for lipid synthesis, detoxification, and calcium storage. It performs several important functions:
- Synthesizes phospholipids and steroid hormones.
- Detoxifies drugs and poisons in liver cells.
- Stores calcium ions in muscle cells (as sarcoplasmic reticulum).
9. How are proteins transported from the ER to the Golgi?
Proteins are transported from the endoplasmic reticulum to the Golgi apparatus through membrane-bound transport vesicles. The process involves:
- Protein synthesis in the rough ER.
- Packaging into small vesicles.
- Fusion of vesicles with the cis face of the Golgi.
10. Why are the endoplasmic reticulum and Golgi body important for the cell?
The endoplasmic reticulum and Golgi body are essential because they enable the synthesis, modification, and distribution of proteins and lipids in eukaryotic cells. Without them:
- Proteins would not be properly folded or transported.
- Lipids and membranes could not be synthesized efficiently.
- Cell secretion and communication would fail.
