2. Lysosomes
• Lysosomes are membrane bound organelles that contain
digestive enzymes.
• They are found in eukaryotic cells primarily animal cells and
plant cells.
• The primary function of lysosomes is extracellular and
intracellular digestion at acidic pH.
• Lysosomes were discovered by De Duve a Belgian Cytologist
in 1955 who designated them as suicide bags.
• De Duve discovered lysosomes in a fraction that was
intermediate between mitochondria and microsomes.
4. Lysosomal Membrane
• The lysosomal membrane contains highly glycosylated lysosomal
associated membrane proteins (LAMP) and lysosomal integral
membrane proteins (LIMP)
• LAMPs and LIMPs coating the inner membrane surface protect the
membrane against attack by enzymes retained within lysosomes.
• An ATP dependant proton pump in the membrane pumps H+ into the
lumen, creating an acidic pH necessary for lysosomal enzymes to
function.
5.
6. Morphology of Lysosomes
• Lysosomes have the
remarkable
characteristic of
pleomorphism
• i.e size and shape of the
particle and
irregularities of its inner
structure.
• In a cell ,lysosomes are
surrounded by smooth
or coated vesicles.
7. Manufacturing Lysosomes
• Lysosomes are manufactured by
golgi apparatus and budded out into
the cytoplasm with enzymes inside
them.
• The lysosomal enzymes are made by
ribosomes and sent to E.R. where
they are tagged with mannose 6
phosphate for being recognized by
receptors of their next destination-
the Golgi apparatus.
• The Golgi Apparatus bud off to form
lysosomes.
8. Types of Lysosomes
Primary lysosomes (storage
granules) are small saclike
structures enclosing enzymes
synthesized by Ribosomes and
stored in E.R. and transferred
to Golgi apparatus.
Heterophagosome(Digestive
Vacuole) The materials
engulfed through phagocytosis
are digested by enzymes of
primary lysosomes.
Residual Bodies are formed in
case of incomplete digestion.
In amoeba they are removed
by defecation otherwise they
are accumulated like pigment
inclusions in nerve cells.
Autophagic Vacuole: A special
scenario in normal cells where
a part of the cell (
mitochondrion or E.R) is in
lysosome for digestion.
9. Secondary Lysosomes
• The Secondary lysosomes
contain materials engulfed by
phagocytosis or pinocytosis
fused with primary lysosomes.
These materials are subjected
to cellular digestion by the
primary lysosomes enzymes.
• Hence, a secondary vacuole
can also be designated as a
digestive vacuole.
11. Autophagy
• Autophagy is a
physiological process for
digestion of cells in the
body to maintain
homeostasis.
• It maintains homeostasis
by protein degradation
and turnover of the
destroyed organelles for
new cell formation.
12. Autolysis
• Autolysis refers to the digestion
of parent cells by the lysosomes.
• Autolysis occurs during
amphibian metamorphosis for
instance the autolysis of tadpole
tail cells.
13. Fertilization
• During fertilization , the nuclear
acrosome of the sperm which is
considered a giant lysosome
secretes hyaluronidase enzyme on
the surface of egg cell. This
disperses the cells around the egg.
Secondly, protease is also
secreted to dissolve zona pelucida
making a channel for the sperm to
enter the egg.
14. Heterophagy
• Heterophagy is the process
of lysosomal digestion of
extracellular materials
entering the cell by the
process of phagocytosis,
pinocytosis and receptor
mediated endocytosis.
15. Programmed cell death
• Lysosomal membrane permeabilization (LMP) induces
controlled cell death as it ensures the translocation of
lysosomal enzymes into the cytoplasm.
• Cathepsins B, L and C are proteases implicated in cell
death they initiate the cascade leading to PCD.
16. Lysosomal Storage Diseases
• LSDs are metabolic disorders where lysosmal enzyme fail to function
properly. As a consequence of which the substrate is accumulated.
• When a lysosomal enzyme is deficient or malfunctioning, the substrate it
targets accumulates, interfering with normal cellular activity.
• These diseases include Tay Sachs disease and Gauchers Disease.
• Healthy Cell Cell with accumulated Substrate
17. Peroxisomes
• Peroxisomes are single membrane bound organelles found
in the cytoplasm of eukaryotic cells
• Peroxisomes originate from Golgi Apparatus.
• They were discovered by De Duve in 1965 in liver cells.
• Peroxisomes are the site of synthesis and degradation of
Hydrogen Peroxide hence designated as peroxisomes.
• An enzyme catalase, a type of oxidase, is present in large
quantity in peroxisomes.
• Peroxisomes self replicate through fission.
18. Anatomy of Peroxisomes
• Peroxisomes have a lipid
bilayer membrane that
controls what enters and
exits them.
• Peroxisomes have a
Urate oxidase crystalline
core with 32 peroxins
(peroxisomal proteins),
that execute peroxisomal
functions inside the
organelle.
19. Functions of Peroxisomes
• They are involved in many different activities like the
degradation of hydrogen peroxide by Catalase.
• For this purpose peroxisomes need significant amount of
Oxygen.
• Initially many oxidases bind with oxygen and hydrogen
to form Hydrogen peroxide.
• In the next step Hydrogen Peroxide is oxidized by
catalase into water and oxygen.
• Peroxidase detoxify alcohol from liver cells.
• Peroxisomes execute the ß-oxidation of Long Chain
Fatty Acids - a major source of energy.
20. Peroxisomal Disorders
• Peroxisomal disorders in humans result due to
abnormal function of an enzyme necessary for
normal peroxisomal function.
• This may result in peroxisomal disorders like:
1.Liver dysfunction
2.Retinopathy
21. References
• Chapter 10 Lysosomes, Endosomes, Coated
vesicles and peroxisomes from cell and
molecular biology by De Robertis.
