1. GOLGI APPARATUS, LYSOSOMES AND VACUOLES
Dr. Saji Mariam George
Associate Professor (Retired)
Assumption College Autonomous
Changanacherry
2. I. GOLGI APPARATUS
(GOLGI COMPLEX, GOLGIBODIES)
• Golgi apparatus is a cell organelle
present in all eukaryotic cells, except
red blood corpuscles(RBCs), sperm
cells of Bryophytes and Pteridophytes
and sieve tubes of plants - discovered
by Camillo Golgi (1898) in the
cytoplasm of nerve cells of an owl.
• The localization, size and
development of Golgi apparatus vary
from one cell to another.
• Most of the Golgi apparatus appears
to be surrounded by a zone which is
free of ribosomes, glycogen and
mitochondria – Zone of exclusion.
Camillo Golgi
3. ULTRASTRUCTURE OF GOLGI APPARATUS
• Structural organization of Golgi apparatus varies
among eukaryotes.
Golgi apparatus consists of
i) Cisternae
ii) Tubules
iii) Vesicles
4. i) Cisternae (Lamellae)
• Double membrane bound, flattened, curved,
sac like structures filled with a fluid. The lumen
of the Golgi cisternae are usually narrow (10nm
-20nm).
• Cisternae are arranged in parallel stacks. The
cisternal stacks (Golgi stacks) are called
dictyosomes.
• Within each dictyosome, the cisternae are
separated from one another by a space of 20
nm to 30 nm and exhibit co-ordinated function.
5. • In mammalian cells, the Golgi apparatus is
located close to the nucleus and centrosome
and is made up of stacked cisternae, which
are interconnected by tubular elements to
form a single continuous body.
• In plant cells, Golgi apparatus are organized
as individual stacks of cisternae(dictyosomes)
that are dispersed through out the
cytoplasm.
7. • Number of cisternae in Golgi stacks varies
from one cell type to another.
• In most plant cells, the number of cisternae
may vary from 3 to 7. Within a single cell,
cisternal number per stack and diameter
are constant. Cisternae in a particular stack
are individual separate entities, but there
are occasional tubular connections.
8. • Cisternae vary greatly depending on cell type
and their position in the stack.
• Dictyosomes ( cisternal stack or Golgi stack) are
polarized structures in that cisternae at one pole
or face of the cisternal stack differ from those at
the opposite pole or face. The proximal pole of
each dictyosome is associated with the nuclear
envelope or endoplasmic reticulum. This pole or
face is referred to as the Cis face or forming
face. The opposite pole(the distal pole) is
known as the maturing, secreting or Trans face.
• Golgi cisternae are fenestrated(having
perforations). These fenestrae are necessary for
movement of secretory granules.
10. Golgi apparatus - Transmission Electron Micrograph
credit: modification of work by Louisa Howard
https://opentextbc.ca
11. ii) Tubules
• From the peripheral area of cisternae arise a
complex network of tubules. The tubules are
300 - 500 Å in diameter and may serve to
connect the cisternae of adjacent
dictyosomes.
iii) Vesicles
• The secretions of cisternae are packed in the
vesicles. These vesicles may be either free or
attached to the tubule ends.
12. FUNCTIONS OF GOLGI APPARATUS
1. Golgi apparatus plays an important role in
endocytic and secretory pathways. Golgi
apparatus receives newly synthesized
molecules (proteins, carbohydrates, lipids etc.)
from endoplasmic reticulum. The Golgi
apparatus modifies, sorts and packages
proteins and lipids. Some will remain in the
Golgi apparatus while others, the newly
synthesized lysosomal enzymes will be
transported to the endocytic pathway and
some others to the plasma membrane
(secretory pathway).
13. 2. The Golgi apparatus synthesize certain
polysaccharides from simple sugars. The
plant Golgi apparatus has an important role
in synthesis of large quantities of cell wall
polysaccharides.
3. Golgi apparatus plays an important role in
the glycosidation of lipids (glycolipids) and
proteins (glycoproteins).
14. 4. Secretory granules originating from Golgi
apparatus will fuse with the cell membrane
(plasma membrane) during exocytosis. The
membrane of the granules get incorporated into
the cell membrane and thus contributes to the
renewal of the membrane constituents.
5. In plant cells, the Golgi apparatus synthesizes
pectin and some other carbohydrates
(hemicellulose) necessary for the formation of
cell wall.
6. The Golgi apparatus gives rise to primary
lysosomes by budding from the maturing face of
cisternae.
16. Lysosomes (Gr. Lysis = dissolution, soma =
body)
• Tiny single membrane bound organelle.
• Lysosomes are commonly found in animal
cells.
• Not common in plant cells. But they have
been reported in certain plant cells-
meristematic cells of plant roots (e.g. root tip
cells of maize) , yeast etc.
17. • The number of lysosomes
in a cell varies with the
cell type.
• Lysosomes may be
spherical, ovoid or rarely
tubular in shape.
However, meristematic
cells of plant roots have
irregular lysosomes.
• Lysosome is a tiny
vacuolar structure bound
by a single lipoprotein
membrane.
• The size of the lysosome
varies from 0.2 μm to 0.8
μm. https://microbenotes.com
18. • Lysosome contains a dense , finely granular
fluid which contain a number of hydrolytic
enzymes. At present more than fifty lysosomal
hydrolases are known which are able to digest
most of the biological substances. These
enzymes generally act at acid pH (approximately
at pH 4.6 - acid hydrolases). e.g. acid
phosphatase, cathepsin, beta-glucuronidase(β-
glucuronidase), neuraminidase etc.
• Lysosomal membrane contains a variety of
highly glycosylated integral proteins whose
carbohydrate chains are thought to form a lining
that protects the membrane from the enclosed
hydrolases.
19. Polymorphism in Lysosomes (Types of Lysosomes)
• Lysosomes exhibit polymorphism with regard to the
size of the particle and the irregularities of their
internal structure.
• Polymorphism is the result of the association of the
primary lysosomes with the different materials that
are phagocytosed by the cell.
• Four types of lysosomes are recognized, of which
only the first is the primary lysosome. The other
three are the secondary lysosomes that are formed
by the fusion of a primary lysosome and a
phagosome, which could be either a
heterophagosome or an autophagosome.
20. i) Primary Lysosomes
(Storage granule)
• Dense particles of about 0.4 μm
surrounded by a single
membrane.
• The enzymatic content is
synthesized by ribosomes of the
rough endoplasmic reticulum
(RER) and transferred to Golgi
apparatus where it is packaged
to form the primary Lysosome.
https://pathresidents.com
21. ii) Heterophagosomes (Digestive vacuole)
• These are secondary lysosomes resulting from
the association of primary lysosomes with
vacuoles containing phagocytosed material. The
phagosome fuses with a primary lysosome and
form the heterophagosome and is digested by
the hydrolytic enzymes.
iii) Residual bodies
• Secondary lysosomes containing indigestible
material are known as residual bodies. In some
cells , they remain for a long time in the cell as
pigment inclusions and may be related to the
ageing process.
22. iv) The autophagic vacuole
(Cytolysosome or Autophagosome)
• The autophagic vacuole is a special case in which
parts of the cell are digested.
• This process is stimulated during starvation and
pathological conditions. Under such conditions,
the lysosomes bring about the digestion of
cellular organelles like mitochondria and
endoplasmic reticulum. This process is known as
autophagy (autolysis). Because of this self
destructive nature, lysosomes are called as
‘suicidal bags’.
23. Polymorphism in Lysosomes- Primary lysosomes,
Heterophagosomes, Residual bodies and Autophagic
vacuoles(Autophagosomes)
24. Functions of Lysosomes
Some of the important functions of lysosomes include
1. Intracellular digestion
• Lysosomes enclose a number of hydrolytic enzymes that
are involved in the mechanism of cellular digestion.
• The digestion of the phagocytosed material takes place
with the help of the hydrolytic enzymes of lysosomes.
Many unicellular organisms ingest food particles which
are enzymatically disassembled in a lysosome. The
lysosomal enzymes digest protein into dipeptides and
carbohydrates into monosaccharides. The resulting
nutrients pass through the lysosomal membrane into the
cytosol.
25. 2. Autophagy
• Regulated destruction of cell’s own organelles and their
replacement. Through the process of autophagy,
lysosomes are involved in the renovation and turnover
of cellular components.
3. Degradation of extracellular material
• Lysosomes are involved in specific processes outside the
cell. This involves the release of primary lysosomes by
exocytosis for degradation of extracellular moieties. This
occurs when the target to be degraded can not be
internalized by endocytosis.
e.g. Lysosomes are involved in the bone-degrading
capacity of osteoclasts - in bone remodelling(osteoclast
is a type of bone cell that breaks down bone tissue ).
4. Crinophagy
• A process by which excess secretory granules are
removed.
26. III. VACUOLES
• Vacuoles are bubble like sacs which are
bounded by a single semipermeable
membrane called tonoplast.
• They are found in most cells.
• Young plant cells have no vacuoles or if
present, are very small in size. But as the cell
matures, the small vacuoles fuse and form a
large central vacuole pushing the cytoplasm
and nucleus to the periphery.
27. • The vacuoles are filled with a fluid called cell
sap. The cell sap consists of free water and a
variety of compounds such as mineral ions,
sugars, oxygen, carbon dioxide, pigments,
organic acids, waste products etc., either in the
form of solution or as crystals.
• The semipermeable membrane tonoplast helps
to maintain concentration of materials different
from that found in the cytoplasmic matrix. They
help to maintain the turgor of plant cells.
• Vacuoles may act as storage organs.
