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PEROXISOME,
CENTRIOLE
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Peroxisomeswere first discovered by
Christian de Duve.
All animal cells (except erythrocytes)
contain peroxisomes.They are roughly
spherical and single membrane-enclosed
organelles.
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Peroxisomes contain about 50 different
enzymes.
They have crystallineand non-crystallineinclusions.
Peroxisomes do not contain DNAor
ribosomes
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Peroxisomes have important roles in the
cell metabolism by oxidizingfatty acids,
bile acids andcholesteroland by
converting hydrogen peroxide towater.
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Catalase, a major peroxisomal enzyme,
converthydrogen peroxide to waterand oxidizes organic compounds (CH
2)
e.g. uric acid and fatty acids.
2H2O
2CATALASE 2H
2O+ O
2
H2O
2+ CH
2CATALASE 2H
2O+ C
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In animal cells, fatty acids are oxidized
in both peroxisomes and mitochondria.
Oxidation of very long chain fatty
acidsoccurs inperoxisomes and
is not linked to ATP production.
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In mammal liver and kidney cells,
varioustoxic moleculesare degraded
in peroxisomes: e.g. hepatic
peroxidation of ethanol produces
acetaldehyde.
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Peroxisomes participate in
the biosynthesis of lipids
Cholesterol anddolichol
Plasmalogens,
Bile acids.
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Peroxisome Biogenesis
Peroxisomes biogenesis has been unclear.
Recent experiments indicate that new
peroxisomes originate from the endoplasmic
reticulum.
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Lack of peroxisomes or dysfunction
A mutation in peroxin 2 (Pex2), a peroxisomal
membrane protein involved in import process,
causes one form of Zellweger syndrome.
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X-linked adrenoleukodystrophy
is a disease that affects the degradation
of very long-chain fatty acids.
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CENTRIOLE
The centriole consist of nine triplets of
microtubules.
Centrioles are found at the base of cilia
and flagella. Basal bodies have a structure
similar to each centriole.
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In animal cells, centrosomesconsist of a paircentrioles surrounded by amorphous material
called pericentriolar material.
The centrosome is the major microtubule-
organizing center (MTOC).
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The centrosome contains the -tubulin ring
complexes that nucleate microtubule growth.
The centrosome duplicates and splits into two
equal parts during interphase (=G1, S, and G2).
During mitosis, duplicated centrosomes
separate and microtubules reorganize to form
the mitotic spindle.
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CENTROSOMES AND CANCER
Tumor cells have abnormalities of centrosome
number and/or stability.
Multipolar mitotic spindle formation is a
diagnostic marker of HPV-associated neoplasias.
Human papillomavirus type 16 E7 oncoprotein
induces centrosome overduplication.
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REFERENCES
1-Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P. :
Molecular Biology of The Cell. Fifth Edition Garland Science Taylor &
Francis Group New York 2008.
2-Pollard T.D. and Earnshaw W.C. : Cell Biology. Second Edition.
Saunders Elsevier USA 2008.
3-Lodish H, Berk A, Kaiser C A, Krieger M, Scott M P, Bretscher A,
Ploegh H, Matsudaira P: Molecular Cell Biology. Sixth Edition. W.H.
Freeman and Company New York 2008.4- Weaver R.F. : Molecular Biology. Third Edition McGraw-Hill, New York
1999.
5-Cooper G.M. and Hausman R.E. : The Cell: A molecular Approach 5th
Edition. ASM Press Sinauer Associates Inc. USA 2009.
6-Epstein R.J. : Human Molecular Biology. Cambridge University PressUK 2003.
7-Kierszenbaum A. L. and Tres L.L.: Histology and Cell Biology: An
Introduction to Pathology. Third Edition. Mosby Elsevier USA 2012.