ctf peroxisome

8/13/2019 CTF Peroxisome

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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.

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