Golgi apparatus: Definition, Types, Examples, Diagram, Function

What is the Golgi Apparatus?

Golgi is found in the eukaryotic cell cytoplasm as a stack of flattened membrane sacs near the rough ER. The number of these membrane sacs varies with the cell type, ranging from 2–3 to as many as 60. The specialised secretory cells, such as goblet cells of the intestinal epithelium have more Golgi sacs than other cells. Golgi apparatus is known to sort, modify and transport the newly synthesised proteins and lipids to their designated addresses.

Historical Background of Golgi Apparatus

The Golgi apparatus was discovered by Italian scientist Camillo Golgi in 1898 employing a new staining method. Subsequently, research has added more information to the body of knowledge regarding this organelle mainly to reveal the fact that the Golgi apparatus is a significant player in the secretory processes, protein synthesis, and restoring the structural and functional order of the cell.

Structure of Golgi Apparatus

The structure of the Golgi Apparatus is described below-

General Structure – Cisternae

The membrane sacs are called cisternae. Structurally, the Golgi apparatus is divided into three parts: cis Golgi, medial Golgi, and trans-Golgi. Each part of the Golgi apparatus has different enzymes responsible for the modification of the polypeptides.

Functional Zones – Cis, Medial, Trans Regions

Cis-Golgi Network (CGN): This side of the Golgi apparatus faces the rough ER and the nucleus, through which it receives vesicles from the ER more commonly called the delivery side.

Medial-Golgi: It is present in the middle of cis and trans Golgi. It is the site for the majority of changes in proteins and lipids.

Trans-Golgi Network (TGN): It is away from the ER but closer to the plasma membrane, the exit face, sorted and modified molecules are packaged into vesicles and transported to various destinations.

Functions of Golgi Apparatus

The functions of the golgi apparatus are described below-

Protein Modification (Glycosylation, Phosphorylation)

The various proteins are transported to the Golgi apparatus for glycosylation which involves the addition of sugar groups and phosphorylation which involves the attachment of phosphate groups to proteins.

Sorting and Packaging of Proteins

Proteins enter Golgi apparatus from the cis face. As they move from one side to another they are modified by the enzymes located in the Golgi. Later, the sorting of the proteins into vesicles destined for lysosomes or plasma membrane takes place.

Lipid Transport and Membrane Biogenesis

This organelle plays a role in sorting and packaging lipids and coordinating on where they would be delivered. It has an important function of lipid synthesis which provides a means for the formation of cell membranes.

Polysaccharide Synthesis (Plants & Animals)

In plant cells, Golgi apparatus also makes polysaccharides such as pectin and hemicellulose, which are incorporated into the cell wall.

In animal cells, it synthesizes glycosaminoglycans and proteoglycans which are major matrices of the extracellular matrix.

Vesicular Transport

The Golgi apparatus sorts proteins and lipids into vesicles that are to be delivered to their appropriate destinations.

Dynamics and Regulation of Golgi Apparatus

The dynamics and functional regulation of the Golgi Apparatus is described below-

ER–Golgi Interaction

ER products, proteins and lipids, are shipped to the Golgi apparatus through vesicles that are formed and bud off the ER, fusing with the cisternae of the cis-Golgi network.

Vesicle Transport to Lysosomes & Plasma Membrane

They process, sort, and package proteins and lipids that are sent to lysosomes or plasma membrane or that are to be secreted. These molecules are transported on vesicles originating from the trans-Golgi network (TGN) to their appropriate locations.

Regulatory Mechanisms (Rab & Arf GTPases)

Signalling pathways: Signaling molecules control the actions of the Golgi apparatus some of which are Rab and Arf GTPases involved in vesicle formation.

Adaptation to cellular needs and stress: This organelle can also respond to other conditions of the cell, for instance, when production and secretion of proteins or when stressed, the Golgi apparatus modifies it to ensure that the condition of the cell is received well.

Biogenesis and Maintenance of Golgi Apparatus

The biogenesis and maintenance of the Golgi apparatus is described below:

Origin from ER Vesicles

The Golgi apparatus develops from some vesicles that come from the endoplasmic reticulum (ER). These form vesicles, which come together to form the cis-Golgi, transforming into the medial-Golgi, and finally the trans-Golgi, which is involved in the packaging and shipment of products in the body.

The structure and activity of the Golgi apparatus are regulated by multiple genetic factors: the presence of genes encoding Golgi matrix proteins and enzymes of vesicular traffic. External factors regulate the internal signalling pathways that are involved in the process of Golgi movement and formation depending on nutrient access and other cellular stressors.

Role of Golgi Matrix Proteins (GRASPs, Golgins)

The structure and function of the Golgi apparatus are constantly undergoing a process of vesicle budding and fusion through the assistance of coat protein complexes including COPI as well as COPII. Therefore, a constant traffic of vesicles that play a role in the replacement and distribution of Golgi enzymes and other resident proteins.

The proteins included in the GM are also referred to as GRASPs (Golgi reassembly and stacking proteins) and golgins which are important in sustaining the structural organization and nesting of the cisternae.

Applications and Relevance

The applications and relevance of the Golgi apparatus are described below-

Medical Significance (Diseases, Cancer)

Defects in most components of the Golgi apparatus result in incompetent protein folding and sorting can cause various diseases such as the congenital disorders of glycosylation and even some types of cancer in which the rates of glycosylation affect signaling and tumor growth.

Biotechnology and Drug Development

It has been a subject of the drug and genetic engineering process since the delivery and efficiency of therapeutic proteins are performed in the Golgi apparatus. Understanding how Golgi takes part in protein modification and sorting is useful in coming up with strategies for generating recombinant proteins, enhancing the stability and activity of these proteins in their status as drugs.

Golgi Apparatus NEET MCQs (With Answers & Explanations)

Important topics for NEET exam are:

• Structure of Golgi apparatus (cisternae and its types)

• Functions of Golgi apparatus

Practice Questions for NEET

Q1. Surface of Golgi cisternae towards nucleus is____________ face and towards plasma membrane is ______ face

1. trans, cis

2. maturing, forming

3. maturing, trans

4. cis, maturing

Correct answer: 4) cis, maturing

Explanation:

The Golgi complex is made of many numbers of cisternae that are concentrically arranged near the nucleus. This part facing the nucleus is convex in shape and known as the cis face, or forming face as it receives incoming materials. On the contrary, the convex surface facing outwards is also called the trans face or the maturing face, where all the processed material is sorted out and dispatched accordingly for transport within or outside the cell.

Hence, the correct answer is option 4) cis, maturing.

Q2. The Golgi apparatus remains in close association with the endoplasmic reticulum, because

1. Materials packaged by the Golgi apparatus are transported to the ER.

2. Materials to be packaged by the Golgi body and transported to the Golgi body from the ER.

3. Both the Golgi body and the ER have cisternae.

4. Both the Golgi body and the ER have ribosomes.

Correct answer: 2) materials to be packaged by the Golgi body and transported to the Golgi body from the ER.

Explanation:

The Golgi apparatus maintains proximity to the endoplasmic reticulum due to their intertwined roles in protein and lipid creation, alteration, and trafficking.

Explanation:
1. Vesicle-Mediated Transport:
Proteins from rough ER and lipids from smooth ER are encapsulated in vesicles for Golgi transfer, necessitating proximity for efficient delivery.
2. Modification and Categorization:
Golgi processes proteins (e.g., glycosylation) and organizes them for transport to specific cell locations, like secretion, membrane integration, or lysosomal targeting, which they receive directly from the ER.
3. Vesicle Exchange:
Vesicles shuttle materials from ER to Golgi, guaranteeing a swift and organized movement of synthesized substances for further processing.
4. Functional Linkage:
The Golgi's cis-face points towards the ER, facilitating a smooth material flow, while the trans-face dispatches the processed molecules to various cell parts, highlighting their functional continuity.

Hence, the correct answer is option 2) Materials to be packaged by the Golgi body and transported to the Golgi body from the ER.

Q3. Assertion(A): Endoplasmic reticulum, lysosomes, vacuoles and golgi complex together forms the endomembrane system.

Reason(R): The functions of ER, lysosomes,golgi complex and peroxisomes are in coordination with each other.

1. (A) and (R) both are true, but (R) is not the correct explanation of (A).

2. (A) is true, but (R) is false.

3. (A) is false, but (R) is true.

4. (A) and(R) both are correct and (R) is the correct explanation of (A).

Correct answer: 2) (A) is true, but (R) is false

Explanation:

Option 2 is the correct answer because the given assertion (A) is true as ER, lysosomes, vacuoles, and Golgi complex together form the endomembrane system. Therefore, their functions are coordinated as they are part of the endomembrane system. But the reason (R) is false because peroxisomes are not part of the endomembrane system. Therefore, the functions of ER, lysosomes, Golgi complex, and peroxisomes are not in coordination with each other.

Hence, the correct answer is option 2) (A) is true, but (R) is false.

Also Read:

• MCQs on Golgi Apparatus

• Endomembrane System

• Flagella

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