Golgi Apparatus
Introduction
The Golgi apparatus (also called Golgi complex or Golgi body) is a vital cell organelle found in all eukaryotic cells. It was discovered by Camillo Golgi in 1898 while studying nerve cells. The Golgi apparatus plays a key role in the modification, packaging, and transport of proteins and lipids synthesized in the endoplasmic reticulum (ER).
Structure
The Golgi apparatus consists of flattened, membrane-bound sacs called cisternae along with associated vesicles and tubules. It shows polarity with two distinct faces – the cis-face (forming face) and the trans-face (maturing face).
1. Cis-face: The receiving side, located near the ER, where vesicles fuse and deliver contents.
2. Trans-face: The shipping side, where processed materials are packaged into vesicles for transport.
3. Cisternae: Usually 4–8 flattened sacs arranged in stacks forming a curved structure.
4. Vesicles: Transport and secretory vesicles involved in movement and export of materials.
Chemical Composition
Golgi membranes are composed of phospholipids and proteins. The lumen contains enzymes responsible for modification reactions like glycosylation and phosphorylation.
Functions of Golgi Apparatus
1. Protein modification and processing: Proteins from ER are glycosylated and phosphorylated.
2. Lipid metabolism: Synthesizes glycolipids and modifies lipids from the ER.
3. Lysosome formation: Produces primary lysosomes containing hydrolytic enzymes.
4. Packaging and secretion: Packages materials into vesicles for exocytosis.
5. Plasma membrane maintenance: Adds new membrane material and proteins.
6. Polysaccharide synthesis: Synthesizes polysaccharides in plant cells.
Significance
In secretory cells like pancreatic and salivary glands, the Golgi apparatus is highly developed. In plant cells, it is called a dictyosome and performs similar functions.
Mechanism of Transport
Two models explain the movement of materials through the Golgi:
1. Vesicular Transport Model – materials move via small vesicles between cisternae.
2. Cisternal Maturation Model – cisternae themselves mature and progress from cis to trans side.
Clinical Importance
Defects in Golgi function can lead to several diseases such as:
1. Congenital Disorders of Glycosylation (CDG)
2. Neurodegenerative diseases due to improper protein trafficking
Summary Table
Discovered by | Camillo Golgi (1898) |
Structure | Stack of flattened cisternae with cis and trans faces |
Location | Near nucleus and ER |
Main Functions | Protein modification, secretion, lysosome formation |
In Plants | Called Dictyosomes |
Importance | Central in secretion and intracellular transport |
Frequently Asked Questions (FAQs)
1.Q. Who discovered the Golgi apparatus?
Ans: Camillo Golgi in 1898.
2.Q. What is the main function of the Golgi apparatus?
Ans:Modification, packaging, and transport of proteins and lipids.
3.Q. What are dictyosomes?
Ans: Dictyosomes are Golgi apparatus structures found in plant cells.
4.Q. Which face of Golgi is called forming face?
Ans: Cis-face.
5.Q. What is the shape of Golgi cisternae?
Ans: Flattened and stacked membrane-bound sacs.
Multiple Choice Questions (MCQs)
1. Golgi apparatus was discovered by:
a) Robert Hooke
b) Camillo Golgi
c) Schleiden
d) Schwann
Answer: b) Camillo Golgi
2. The trans-face of Golgi is involved in:
a) Receiving vesicles
b) Shipping materials
c) Protein synthesis
d) Lipid oxidation
Answer: b) Shipping materials
3. In plants, Golgi apparatus is called:
a) Dictyosom
b) Plastid
c) Lysosome
d) Tonoplast
Answer: a) Dictyosome
4. The Golgi apparatus is mainly involved in:
a) ATP production
b) Secretion and packaging
c) Photosynthesis
d) Respiration
Answer: b) Secretion and packaging
5. Which of the following is NOT a function of Golgi?
a) Protein modification
b) DNA replication
c) Lysosome formation
d) Lipid packaging
Answer: b) DNA replication
Worksheet / Practice Questions
1. Draw and label a neat diagram of Golgi apparatus.
2. Write a note on the functions of Golgi apparatus.
3. Differentiate between cis-face and trans-face of Golgi apparatus.
4. Explain the role of Golgi apparatus in lysosome formation.
5. Describe the cisternal maturation model of transport.
References
1. Alberts, B. et al. (2017). Molecular Biology of the Cell. 6th Edition, Garland Science.
2. Lodish, H. et al. (2021). Molecular Cell Biology. 9th Edition, W. H. Freeman and Company.
3. Cooper, G. M. (2019). The Cell: A Molecular Approach. Sinauer Associates.
4. Online Resource: https://www.zoologys.co.in
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