Microbodies Tamboli A.Z. - PowerPoint Presentation

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Microbodies

Tamboli

A.Z.

F.Y.B.Sc.

Dept. of Zoology , S.M.Joshi College, Hadapsar.

Introduction:

Microbodies

were first reported at the ultra structural level in the proximal convoluted tubule of mouse kidney by

Rhodin

in

1954

.Microbodies are now recognized as ubiquitous subcellular respiratory organelles in eukaryotic cells .

Microbodies

from all tissues appear

morphologically similar

and have

similar enzymatic properties

, but the metabolic pathways within this subcellular compartment vary, depending upon the tissue..

Microbodies

(

peroxisomes and

glyoxysomes

) were one of the last major subcellular compartments to be recognized, and it was not until the end of the 1960s that their significance was established by several reviews. A

microbody

is a type of organelle that is found in the cells of plants, protozoa, and animals. Organelles in the

microbody

family include

peroxisomes,glyoxysomes

,

glycosomes

and

hydrogenosomes

. In vertebrates,

microbodies

are especially prevalent in the liver and kidney organs

History:

Microbodies

were first discovered and named in 1954 by

Rhodin

Two years later in 1956

,

Rouiller

and Bernhard

presented the first worldwide accepted images of

microbodies

in liver cells

Then in 1965, Christian

de Duve

and coworkers isolated

microbodies

from the liver of a rat. De Duve also believed that the name

Microbody

was too general and choose the name of

Peroxisome

because of its relationship with hydrogen peroxide .

In

1967,

Breidenbach

and

Beevers

were the first to isolate

microbodies

from plants, which they named

Glyoxysomes

because they were found to contain enzymes of the

Glyoxylate

cycle.

Morphology

A

microbody

is usually a vesicle with a spherical shape, ranging from 0.2-1.5 micrometers in diameter.

Microbodies

are found in the cytoplasm of a cell, but they are only visible with the use of an electron microscope. They are surrounded by a single phospholipid bilayer membrane and they contain a matrix of intracellular material including enzymes and other proteins, but they do not seem to contain any genetic material to allow them to self-replicate

.

Microbodies

are morphologically characterized as which are delimited by a single tripartite membrane and contain a finely granular matrix . In liver, an estimation of

1,000

microbodies

per hepatocyte

has been

made.They

show a close spatial relationship to the endoplasmic reticulum. Their catalase can be demonstrated

cytochemically

. Because

microbodies

without inner membranes must be pliable, they usually appear spherical or ovoid, but in the cell they may also be irregular in shape or show unusual projections .

Fig:Structure

of

Microbody

T

ypes of

microbodies

There are two types of

microbodies

namely:

Peroxisomes

Glyoxisomes

Peroxisomes

These (

also called

microbodies

) are organelles found in virtually all eukaryotic cells Called

Peroxisomes

because of their ability to produce or utilize Hydrogen

peroxide.They

are small, oval or spherical in

shape.They

have a fine network of tubules in their

matrix.About

50 enzymes have been identified. The number of enzymes fluctuates according to the function of the cells. These were identified as organelles by the Belgian cytologist Christian

de Duve

in

1967

after they had been first described by a Swedish doctoral student,

J.

Rhodin

in

1954

.

However, peroxisomes bud off from the endoplasmic reticulum, not the Golgi apparatus (that is the source of lysosomes). The enzymes and other proteins destined for peroxisomes are synthesized in the cytosol. Each contains a

peroxisomal

targeting signal (PTS) that binds to a receptor molecule that takes the protein into the peroxisome and then returns for another load

.

Peroxisomal

diseases

It represent a class of medical conditions caused by defects in peroxisome

functions.This

may be due to defects in single enzymes important for peroxisome function or in

peroxins

, proteins encoded by PEX genes that are critical for normal peroxisome assembly and biogenesis.

Peroxisomal

diseases include:

ALD :

adrenoleukodystrophy

ZS:

Zellweger

syndrome

1.

Adrenoleukodystrophy

Syndrome

Adrenoleukodystrophy

or ALD results in the over-accumulation of very long chain fatty acids or VLCFA and branched chain fatty acids, such as

phytanic

acid. In addition, PBD-ZSD patients show deficient levels of

plasmalogens

, ether-phospholipids necessary for normal brain and lung function

Zellweger syndrome

:

also called

cerebrohepatorenal

syndrome

, is a rare congenital disorder characterized by the reduction or absence of functional peroxisomes in the cells of an individual. It is one of a family of disorders called

leukodystrophies

.

Zellweger

syndrome is named after

Hans

Zellweger

(1909–1990), a Swiss-American pediatrician. These are autosomal recessive developmental brain disorders that also result in skeletal and craniofacial

dysmorphism

, liver dysfunction, progressive sensory neural hearing loss, and retinopathy

Functions

Peroxisomes perform many functions which include:

Breakdown (by oxidation) of excess fatty acids.

Breakdown of hydrogen peroxide (H2O2), a potentially dangerous product of fatty-acid oxidation. It is catalyzed by the enzyme catalase.

Participates in the synthesis of cholesterol. One of the enzymes involved, HMG-CoA

reductase

, is the target of the popular cholesterol-lowering "statins".

Participates in the synthesis of bile acids.

Participates in the synthesis of the lipids used to make myelin.

Breakdown of excess purines (AMP, GMP) to uric acid

Glyoxisomes

These are specialized peroxisomes found in plants (particularly in the fat storage tissues of germinating seeds) and also in filamentous fungi. As in all peroxisomes, in

glyoxysomes

the fatty acids are hydrolyzed to acetyl-CoA by

peroxisomal

β-oxidation enzymes. Besides

peroxisomal

functions,

glyoxysomes

possess additionally the key enzymes of

glyoxylate

cycle (

isocitrate

lyase

and malate synthase) which accomplish the

glyoxylate

cycle

bypass.Thus

,

glyoxysomes

(as all peroxisomes) contain enzymes that initiate the breakdown of fatty acids and additionally possess the enzymes to produce intermediate products for the synthesis of sugars by gluconeogenesis. The seedling uses these sugars synthesized from fats until it is mature enough to produce them by photosynthesis.

Glyoxysomes

also participate in photorespiration and nitrogen metabolism in root nodules

.