Golgi Apparatus in Cell Biology

Golgi Complex

• The Golgi complex was first described by Camillo Golgi in 1897 as anastomosing threads called the "internal reticular apparatus" in neurons.
• It was later renamed the Golgi apparatus in 1898 and was one of the first organelles described by light microscopists.

Structure of Golgi Complex

• The Golgi complex consists of flattened, membrane-enclosed, disc-shaped compartments called cisternae.
• Each Golgi complex consists of four to six cisternae connected by tubular connections.
• There are three membrane-enclosed components in the Golgi complex: cisternae, small vesicles, and larger vacuoles.

Components of Golgi Complex

• Cisternae: flattened sacs or saccules often slightly curved with convex and concave surfaces.
• Small vesicles: transport vesicles formed from the GER membrane by budding, carrying newly synthesized proteins to the Golgi complex.
• Larger vacuoles: membrane-limited spherical condensing vacuoles associated with the concave inner surface, containing secretory products or glycoproteins.

Function of Golgi Complex

• The Golgi complex receives proteins and lipids from the endoplasmic reticulum (ER) and modifies them.
• The Golgi complex has two distinct poles: cis-face (entry face) and trans-face (exit face).
• Proteins enter the Golgi complex at the cis-face and exit at the trans-face after processing.

Functional Regions of Golgi Complex

• The Golgi complex has five functional regions: cis-Golgi network (CGN), cis-Golgi, medial-Golgi, trans-Golgi, and trans-Golgi network (TGN).
• Each region contains different enzymes that modify proteins.
• The primary function of the Golgi apparatus is the processing of proteins targeted to plasma membrane, lysosomes, endosomes, secretory granules, and sorting and packaging them into specific transport vesicles.

Functions of Golgi Complex

• Processing of proteins targeted to the plasma membrane, lysosomes, and secretory granules.
• Glycosylation of proteins.
• Modification of carbohydrates.
• Proteolytic processing of protein precursors.
• Glycolipid and sphingomyelin biosynthesis.
• Sorting of proteins.

Modification of Proteins in Golgi Complex

• Glycosylation: further steps of glycosylation occur within the Golgi apparatus, with membrane-anchored enzymes modifying N-glycans bound to asparagine residues of proteins.
• Protein processing involves modification and synthesis of carbohydrate portions of glycoproteins, including modification of N-linked oligosaccharides.