golgi bodies

1. GOLGI BODIES

2. •Golgi bodies are aggregations of membrane-bound
spaces, which serve as the centres of cellular
secretion.
•They are particularly abundant in secretory cells.
•They form a specialised part of the endomembrane
system, and serve as the centres of cellular secretion.
•They are primarily concerned with the concentration,
chemical modification and packaging of synthetic
products as secretory granules or droplets.

3. DISCOVERIES
• Early observations of Golgi bodies were made by St. George, Plattner,
Hermann and others.
• But, Vacuoles they were first discovered and described by Camillo Golgi
(1898).
• He termed them "apparato reticulare interno" (internal reticular apparatus).
• Since then, they came to be known variously as Golgi bodies, G. complex, G.
apparatus, G. vesicles, and so on.
• Baker (1951) proposed the name lipochondrins, considering their presumed
lipid content.
• Plant Golgi bodies are often described as dictyosomes.

4. Camillo Golgi (1898)

5. • Golgi bodies occur in all kinds of cells, excepting prokaryotes and mature
mammalian RBCs.
• Their location, number and size are different in different cell types.
• In secretory cells, they are usually seen in between the nucleus and the apical
pole.
• But in nerve cells, they occupy a circum-nuclear position.
• In most cells, there is only a single set of Golgi bodies.
• But, invertebrate cells, nerve cells, liver cells and most plant cells have multiple
sets, more or less distributed throughout the cytoplasm.
• Multiple sets of Golgi bodies are described dictyosomes.
• In salivary gland cells, they are exceptionally numerous, often several
thousand.

8. Morphology
• Golgi bodies are essentially membrane-bound spaces.
• They are of three kinds, namely lamellae, vesicles and
vacuoles.
• Lamellae form the core units of Golgi bodies.
• Vesicles and vacuoles remain crowded around them in
clusters.
• The internal lumen of lamellae is called cisterna.
• Lamellae are flattened sacs, with dilated ends.
• They are arranged in parallel stacks or piles, often called
golgiosomes.

10. •Vesicles are groups of small membrane-bound spaces,
and vacuoles are large and scattered membrane-bound
sacs.
•Vesicles, vacuoles and the dilated ends of lamellae may
be filled with a granular or amorphous material.
•In some cases, the spaces between adjacent lamellae
(interlamellar spaces) may also be filled with a similar
material.
•Its composition and functions are not definitely known.
•Probably, it may serve as a cementing substance.

11. •Lamellar membranes are always in dynamic equilibrium.
•They are constantly budded off from the SER and, at the same
time, lost for the formation of secretory vesicles.
•In goblet cells, they get transformed to mucilage granules,
which almost fill the whole cell.
•Each lamella has a polarised orientation.
•It has a convex outer side or face, known as the "forming
face", entry face, or cis face, and a concave inner face, known
as "maturing face" (exit face or trans face).

12. •The forming face receives vesicles from ER, whereas
maturing face gives out a large number of secretory
vesicles.
•The forming face is oriented towards RER or nuclear
envelope, and the maturing face towards the cell
surface.
•Each face is closely associated with a network of
tubules, forming the so called cis Golgi network and
trans Golgi network.

13. •A lamellar stack contains three major kinds of sacs with
different functions. They are cis sacs, trans sacs and
medial sacs.
•Cis sacs are located towards the outer or cis face of the
stack, trans sacs are located towards the inner or trans
face, and medial sacs are seen in the middle of the
stack.
•Cis sacs are mainly concerned with the phosphorylation
of the mannose molecules of the glycoproteins that are
destined to pass to lysosomes.
•This phosphorylation serves as a specific signal to direct
proteins to lysosomes.

14. •Medial sacs are involved in the removal of mannose
molecules and the addition of acetyl glucosamine to the
glycoproteins that are destined for exocytosis through plasma
membrane.
•The removal of mannose molecules is mediated by the
enzymes mannosidases, and the addition of acetyl
glucosamine is mediated by glycosyl transferases.
•Trans sacs are involved in the addition of galactose and sialic
acid (a modified hexose sugar) to glycoproteins.
•The transport of glycoproteins from cis-to-medial-to-trans
sacs is effected by the vesicles which bud from one sac and
then fuse with the next sac.

15. • In between the forming face and the RER, there are numerous
membrane-bound bodies, called transition vesicles or
transition tubules.
• Often, they converge upon the lamellae and form a
fenestrated plate.
• These transition elements are thought to take their origin
from RER and, by fusion, they form new lamellae.
• This compensates the loss of lamellae at the maturing face.
• Associated with the maturing face, there may be present a
saccular region of SER, known as GERL.

16. • The vesicles of the Golgi complex occur in two forms, namely
smooth-surfaced vesicles and rough-surfaced or "coated vesicles".
• Smooth vesicles are quite common, but rough vesicles are less
frequent.
• The membranes of the rough vesicles are coated with granules or
bristles at the outer (cytoplasmic) surface.
• The functional significance of this morphological distinction is not
definitely understood.
• Golgi bodies have no attached ribosomes.
• Their membranes appear to be surrounded by a small area, often
called the zone of exclusion.
• Here, glycogen, ribosomes and mitochondria are apparently absent.

17. Chemical composition
•Golgi bodies are chemically unstable.
•Their chemical make-up may change from time to time.
•In general, their membranes have lipoprotein composition,
laminar structure and fluidmosaic organization.
•They are formed mainly of proteins and phospholipids, most
usually in the ratio 6:4, or sometimes in almost equal
amounts.
•The presence of low levels of cholesterol, cholesterol esters,
carotenoids, free fatty acids, triglycerides,
mucopolysaccharides, vitamin C, etc. has also been reported
in several cases.

18. •Golgi bodies are rich in a variety of enzymes.
•The enzymes, found in high concentrations, include
thiamine pyrophosphatases and glycosyl transferases.
•Transferases are the most characteristic Golgi enzymes,
and they mediate the synthesis of glycoproteins and
glycolipids by transferring oligosaccharides to proteins
and lipids.
•Some acid phosphatases (such as ADPase, ATPase and
CDPase), phospholipases, oxido-reductases,
transferases, and some lysosomal enzymes may also be
found in Golgi bodies.

20. Biogenesis
• The components of the Golgi complex are constantly re-formed in a more or less
dynamic and cyclic manner
• Different views have been advanced to account for the origin of Golgi
membranes.
• One view is that they arise de novo (anew).
• The second view is that they arise from pre-existing membranes, mainly from
plasma membrane, ER and nuclear membrane.
• The third view is that Golgi lamellae take their origin from SER and then they bud
off the other components.
• The SER is believed to take its origin from RER which, in turn, is formed from
nuclear membrane.

21. Functions
•Golgi bodies are the important chemical factories or secretory
centres of the cell.
•They are involved in the synthesis of substances, storage,
processing and packaging of secretory products as secretory
vesicles, formation of acrosome and primary lysosome,
activation of mitochondria, elaboration of yolk bodies, etc.
•Some of their major functions are the following:
•(i) Serve as an intracellular compartment for the chemical
modification of the substances synthésised elsewhere, and
also for the differentiation and rapid turn over of cellular
membranes.

22. • (ii) Synthesis of mucopolysaccharides, glycoproteins and glycolipids
by glycosylation (addition of sugar residues from a sugar donor). This
takes place in a step by step manner with the help of the enzymes
glycosyl transferases. The donor of sugar units in most cases is
uridine diphosphate glucose (UDPG).
• (iii) Cellular secretion of export proteins, intracellular enzymes (such
as lysosomal and peroxisomal enzymes), hormones, antibodies, yolk
granules, lipid droplets, etc.
• (iv) Secretion of mucus, milk protein, thyroxine compounds, etc.
• (v) Formation and packaging of zymogen granules, melanin granules,
etc.
• (vi) Formation of microbodies and primary lysosomes and the
glycosylation of lysosomal enzymes.

23. • (vii) Formation of acrosome in developing animal sperms, and
the formation of cortical granules and a protective coating in
developing oocytes.
• (viii) Removal and re-cycling of excess membranes and
secretory granules (e.g., zymogen granules).
•(ix) Formation, packaging and transport of cell wall
polysaccharides and pectic compounds for cell wall formation
in plant cells.
•(x) Formation of cell plate during the division of plants cells.
This is accomplished by the condensation of membrane
vesicles which discharge their contents to
reinforce the cell plate.