The Golgi apparatus is an organelle found in most eukaryotes. It consists of a series of flattened membrane sacs called cisternae. These cisternae are present one over the other to form the Golgi complex. It is responsible for packaging proteins into vesicles before secretion and, therefore, plays a key role in the secretory pathway.
Structure of the Golgi Apparatus
The shape and size of the Golgi complex depend upon the physiological state of the cells. Mainly, it is composed of four parts: cisternae, tubules, vesicles, and vacuoles. The structure of the Golgi apparatus is as follows:
- Golgi Apparatus consists of flat, disc-shaped sacs or cisternae of 0.5µm to 1.0µm diameter. These are stacked parallel to each other.
- The Golgi cisternae are concentrically arranged near the nucleus.
- They have distinct convex cis or the forming face and concave trans or the maturing face. These faces are completely different from each other, but are interconnected.
- The organelle has a cis face for receiving materials from the endoplasmic reticulum and a trans face for shipping vesicles to various cellular organs.
- Vesicles move from the cis to the trans face during processing.
- This distinctive structure of the Golgi apparatus allows for efficient processing, modifying, and packaging of macromolecules within the cell
Characteristics of the Golgi Apparatus
It was first discovered by Camillo Golgi in 1898. It is characterised by stacked membrane sacs known as cisternae. These cisternae are stacked on top of each other to form the Golgi complex. Other characteristics are given below:
- The Golgi apparatus is made up of approximately four to eight cisternae, although in some single-celled organisms, it may consist of as many as 60 cisternae. The Golgi consists of cis and trans faces.
- The cis face receives material from the endoplasmic reticulum, and the trans face releases vesicles carrying processed substances to various cellular organs.
- Animal cells generally contain around 10 to 20 Golgi stacks per cell, which are connected by tubular connections.
- The plant cells contain many freely distributed subunits of the Golgi Apparatus, called dictyosomes.
- The Golgi body is not present in bacteria, blue-green algae, mature sperm, and red blood cells of mammals and other animals.
- The various functions performed by the Golgi apparatus are: it modifies and processes lipids for cellular use, contributes to the formation of lysosomes for cellular waste management and modifies proteins by adding carbohydrates and phosphate groups to proteins.
Functions of the Golgi Apparatus
The functions of the Golgi apparatus are as follows:
- The Golgi complex helps in membrane transformation and membrane recycling.
- Proteins synthesised by the rough endoplasmic reticulum reach the cisternae of the Golgi apparatus, where they combine with carbohydrates to form glycoproteins.
- It is essential for proper protein structure and function.
- The Golgi apparatus mediates the production of hormones by endocrine glands.
- It forms the matrix of connective tissue.
- Contributes to the formation of lysosomes for cellular waste management.
- It helps in the formation of root hair from their mother cells.
- It packages macromolecules into vesicles for transport.
- In chick embryos, the retinal pigment is synthesised by the Golgi complex.