Microbodies

 


MICROBODIES:

They are small cell organelles bounded by single membrane. They absorb molecular oxygen and take part in oxidation other that those involved in respiration. The  microbodies are noticeable with electron microscope only.

Discovery: The microbodies were first seen by Rhodin in 1954 in the electron micrographs of mouse kidney tubule cells.



Location:

The microbodies occur in nearly all eukaryotic cells. They usually lie near the endoplasmic reticulum, sometimes near the mitochondria or plastids or both. The microbodies are absent in prokaryotic cells.

 Microbodies  of Structure:


The microbodies are minute, simple, roughly spherical sacs bounded by a single unit membrane. They are 0.5 to 1.5 ųm in size. They contain a densely granular matrix which has a regular core or nucleoid of crystalline material. The latter represents a variety of enzymes. These enzymes catalyse oxidation reactions not involved in respiration. 



Origin:

The microbodies do not bud from the ER or Golgi apparatus. They grow by drawing proteins and lipids made in the cytosol, and multiply by division into two on attaining a certain size.

Microbodies of Types :


The microbodies are of three main types: 
● Animal Peroxisome 

● Glyoxisomes:

● Plant Peroxisomes:

All share catalase activity.

1. Animal Peroxisomes:




The Peroxisomes ( peroxide + soma= body) are abundant in the liver and kidney cells of vertebrates. They are also found in other organs, such as brain, small intestine, testis, and adrenal cortex. They also occur in the invertebrates and protozoans, such as Paramecium.They contain peroxide_ producing enzymes ( oxidases¹) and peroxide _ destroying enzyme( catalase), hence their name.Oxidases catalyse the oxidation of substrates ( amino acids and uric acid), producing hydrogen peroxide ( H2O2) .Molecules oxygen is needed for the production of hydrogen peroxide.Catalase degrades hydrogen peroxide to water and oxygen. Hydrogen peroxide is produced by the cell's biochemical machinery to attack and kill ingested bacteria. However, hydrogen peroxide is harmful to living cells. Its destruction by catalase is, thus, beneficial for the cell.

          Enclosing in the same organelle both the H2O2 producing and H2O2 destroying enzymes also shows that the cell's compartments structure is crucial to its function.

        Peroxisomes help in detoxifying the alcohol in the liver cells by transferring hydrogen from it to oxygen. About 50% of alcohol taken by a person is detoxifies by the liver cell Peroxisomes.

     

2. Glyoxisomes:

The glyoxisomes contain, besides catalase, enzymes that catalyze conversion of fats to sucrose by glyoxylate cycle. Glyoxisomes are found only in the plant cells, particularly in the cells of  germinating fatty seeds, such as castor, watermelon, cucumber, peanut and others. The emergency seedlings use sucrose as energy and carbon source till they are able to produce their own sugar by photosynthesis. After germination of seeds, glyoxisomes are no longer found in the cells.

3. Plant Peroxisomes:


There are found in the leaf cells capable of photosynthesis. There may be 70 to 100 Peroxisomes in a mesophyll cell. They contain enzymes present in both animal Peroxisomes and glyoxisomes. In addition, they have enzyme glycolic acid oxidase that oxidises glycolic acid, a product of photosynthesis, to glycolic acid,a process called photorspiration. The glyoxylic acid may give rise to suuinic acid or change into an amino acid glycine. The succinic acid may enter Krebs cycle or change into glucose. The amino acid glycine takes part in protein synthesis. The plant Peroxisomes have enzymes for all these reactions also.Thus, they are the most complex microbodies.

Function:

The microbodies are oxidative organelles which play an important role in the metabolism of fats, sugars and amino acids. Microbodies take part in various biochemical reactions in the cell. The enzymes present in microbodies facilitie various essential reactions, e.g. breakdown of fats, amino acids, alcohol, etc.They are involved in the  photorespiration in plants.Detoxification of peroxide occurs in microbodies.

Spharerosomes:

Sphaeroosome are small cell organelles found in plant cytoplasm and bounded by single membrane with take part in storage and synthesis  of fats. Spherosomes are refractile  vesicles which arise from the endoplasmic reticulum. 98% of a sphaerosome is fat, remaining 2% being protein. Some proteins are probably  enzymatic  and take part in the synthesis  of fats. Because  of the presence of fat, spherosomes can be seen under light microscope after staining  the cells with Sudan dyes and osmium tetraoxide. They occur abundantly in the endosperm cells of oil seeds. In some tissues  ( e.g., tobacco  endosperm, maize root tip) spherosomes contain hydrolytic enzymes and thus considered to have lysosomes  activity.
  

























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