STRUCTURE AND FUNCTIONS

1. PEROXISOME
STRUCTURE AND FUNCTIONS
DR. DILIP V. HANDE
ASSOCIATE PROFESSOR, DEPT OF BOTANY
SHRI SHIVAJI SCIENCE COLLEGE, AMRAVATI MS.

2. PEROXISOMES
 Structure: spherical
organelles that contain
enzymes within single
membranes
 Function: Degrade hydrogen
peroxide, a toxic compound
that can be produced during
metabolism.

3.  Peroxisomes: Specialized metabolic organelles
that contain peroxide-producing enzymes.
 Bound by a single membrane.
 Contain peroxide-producing enzymes, that
transfer hydrogen from various substrates to
oxygen, producing the toxic hydrogen peroxide
(H2O2).
Contain an enzyme that converts toxic H2O2 to
water.
 Are not part of endo memebrane system; they
grow in size by incorporating proteins and lipids
made in the cytosol.
Increase in number by splitting in two.
Peroxisomes consume oxygen in various metabolic functions

4. LYSOSOMES AND PEROXISOMES
Lysosomes and Peroxisomes are
present in eukaryotes only. Lysosomes
contain digestive enzymes (acid
hydrolases). They digest excess or
worn-out organelles, food particles,
and engulfed viruses or bacteria.
Peroxisomes have enzymes that rid the
cell of toxic peroxides.

5. PEROXISOMES
 Similar to lysosomes
 Membrane-bounded vesicles
 Enclose enzymes
 Enzymes synthesized by free ribosomes in
cytoplasm (instead of ER)
 Active in lipid metabolism
 Catalyze reactions that produce hydrogen
peroxide H2O2
Toxic
Broken down to water & O2 by catalase
5

6. STRUCTURE
 Peroxisomes are smaller ovoid or somewhat spherical granules
with single membrane.
 The average diameter varies from 0.5 to 10.4 µm.
 They contain a fine granular substances in the centre to form a
opaque homogenous core.
 The number of peroxisomes per cell is variable i.e. in between
70-100 in rat liver cell and general cell is having (liver) 15-20
peroxisomes.
 The peroxisomes contain different types of enzymes like
glycolate oxidase, glycolate reductase, catalase, glycolate
transaminase, and malate dehydrogenase.

7. ORIGIN
 These are formed by budding of E.R.
 Some evidences suggested that new
peroxisomes always arise from pre- existing ones
being formed by growth and fission of old
organelles.
 Similar to mitochondria and chloroplasts.

8. FUNCTIONS
 Main function of peroxisomes is help in metabolism of
glycolate synthesized by chloroplasts during photosynthesis.
 They have an ability to reduce oxygen to water by the two
step mechanism involving H2 as intermediate.
 Play important role in photorespiration.
 A major function of the peroxisome is the breakdown of very
long chain fatty acids through beta-oxidation .
 In animal cells, the very long fatty acids are converted to
medium chain fatty acids, which are subsequently shuttled to
mitochondria where they are eventually broken down to
carbon dioxide and water.
 In yeast and plant cells, this process is exclusive for the
peroxisomes

9.  Specialized peroxisomes ( glyoxysomes) are
found in fat storing tissues of plant seeds:
Some functions of peroxisomal reactions
 Breakdown of fatty acids (using oxygen) into
smaller molecules. The products are carried to
mitochondria as fuel for cellular respiration.
 Detoxification of alcohol and other harmful
compounds. In the liver, peroxisomal enzymes transfer
H2 from poisons to O2
 Contains enzymes that convert the fatty acids to
sugars
 These biochemical reactions make energy stored
in seed oils available for the emerging seedling.