Golgi apparatus
Apparatus golgiensis; complexus golgiensis
Also known as: Golgi complex, Golgi body, dictyosome, trans-Golgi network, TGN
A polarised stack of flattened cisternae (cis → medial → trans) that receives proteins from the ER, modifies their sugars, and sorts and packages them for secretion, the plasma membrane or lysosomes.
Overview
Discovered by Camillo Golgi (1898) with silver impregnation, the Golgi apparatus consists of stacks of typically 4–6 (up to ≈8) curved, flattened cisternae with dilated rims, usually located next to the nucleus and the centrosome. It is polarised: the convex cis face (cis-Golgi network) receives COPII-derived cargo from the ER via vesicular–tubular clusters (ERGIC); cargo then passes through medial and trans cisternae — largely by cisternal maturation, in which cisternae progress forward while resident enzymes are returned backward in COPI vesicles — and exits from the concave trans face and trans-Golgi network (TGN).
Enzymes are arranged in assembly-line order: N-linked oligosaccharides from the ER are trimmed (mannose removal) and rebuilt into complex glycans (N-acetylglucosamine, galactose, sialic acid); O-linked glycosylation (on serine/threonine) of mucins and proteoglycans is carried out; glycosaminoglycan chains are sulfated; and some prohormones begin proteolytic processing.
Lysosomal targeting: in the cis-Golgi, N-acetylglucosamine-1-phosphotransferase recognises lysosomal hydrolases and phosphorylates their mannose residues; after an "uncovering enzyme" acts, the exposed mannose-6-phosphate (M6P) binds M6P receptors in the TGN. Clathrin-coated vesicles carry the receptor–enzyme complexes to endosomes, where the acidic pH releases the enzymes and the receptors recycle. At the TGN other cargo is sorted into constitutive secretory vesicles, regulated secretory granules, or apical versus basolateral carriers in polarised epithelia.
- Location
Juxtanuclear, around the centrosome; between the RER and the secretory surface (e.g. supranuclear in goblet and acinar cells).
Parts & subdivisions
- Cis-Golgi network (cis face)Entry face receiving cargo from the ER; site of M6P tagging (phosphotransferase); returns escaped ER proteins (KDEL receptor, COPI).
- Medial cisternaeRemodelling of N-linked glycans; addition of N-acetylglucosamine.
- Trans cisternaeAddition of galactose and sialic acid; sulfation.
- Trans-Golgi network (trans face)Sorting station: lysosomal (M6P receptor/clathrin), constitutive, regulated and polarised routes.
Anatomy
- Histology
In H&E sections an active Golgi appears as a pale perinuclear zone — a negative Golgi image or "hof" — in plasma cells and osteoblasts. In goblet cells it lies between the nucleus and the mucinogen granules.
Function
- Modification of glycoproteins and glycolipids (N- and O-linked glycosylation).
- Sulfation and assembly of proteoglycans.
- Mannose-6-phosphate tagging and sorting of lysosomal enzymes.
- Packaging of secretory products into vesicles and granules.
- Membrane recycling and delivery of new membrane to the cell surface.
Clinical significance
I-cell disease (mucolipidosis II)
Autosomal recessive deficiency of N-acetylglucosamine-1-phosphotransferase (GNPTAB): no M6P tag, so lysosomal hydrolases are secreted (high plasma levels) and lysosomes fill with undigested material ("inclusion" cells). Coarse facies, gingival hyperplasia, skeletal dysplasia, restricted joint movement, death usually in childhood.
Congenital disorders of glycosylation
Defects of ER/Golgi glycosylation enzymes cause multisystem disease (developmental delay, hypotonia, coagulopathy); screened by transferrin glycoform analysis.
Mnemonics
Coat proteins
COPII goes forward (ER → Golgi, anterograde); COP I goes back (Golgi → ER, retrograde); clathrin carries cargo from the trans-Golgi to endosomes/lysosomes and from the plasma membrane inward.
Compiled from standard anatomy and physiology references — see the Cells & Tissues sources. For education only; not medical advice.