Micro bodies of Eukaryotic Cell (With Diagram)

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Micro bodies are small cell organelles bounded by single membrane which absorb molecular oxygen and take part in oxidation other than those involved in respiration.

Discovery:

These submicroscopic bodies were observed for the first time in 1954 in the mouse kidney tubule cells with the help of electron microscope.

Location:

They are present in almost all eukaryotic cells. They are mostly seen near the endoplasmic reticulum (ER), and sometimes near mitochondria and plastids.

They are absent in prokaryotic cells.

Origin:

The micro-bodies pinch off from the rough endoplasmic reticulum (RER) after receiving the enzymes synthesized on RER.

Function:

These are oxidative bodies and play important role in the metabolism of fats, sugars and amino acids.

Types:

Micro-bodies are of two types—peroxisomes and glyoxysomes.

(i) Peroxisomes:

These micro bodies are found in both animals and plants. They were discovered by Rhodin in 1954, and studied in detail by Tolbert in 1969. Since they contain enzymes for peroxidase synthesis, they are called peroxisomes. They are found in close association with ER, mitochondria and chloroplasts.

In animals, they can be seen in liver and kidney cells. They are found in abundance in photosynthesizing cells; and each such cell may contain up to 70-100 peroxisomes. They develop from ER, and their shape and size are variable (mostly 0.5-1.Oµm in diameter).Each peroxisome is covered by a single unit membrane. They have a matrix of fine granules in the central part of which there is a homogeneous and opaque and fibrous core (Fig. 3.35).

Glycolic acid oxidase, peroxidase (smallest enzyme), catalase (largest enzyme) and «–amino acid oxidases are found in high concentration in peroxisomes.

In Animals:

In animal cells, peroxisomes take part in oxidation of a number of bio-chemicals including may also take part in lipid metabolism.

In Plants:

They are found in abundance in plant cells in which photorespiration takes place (i.e., in C₃ plants). During photorespiration, green plants release CO₂ during day time. The peroxisomes contain enzyme glycolic acid oxidase that oxidises glycolic acid, a product of photosynthesis, to glyoxylic acid, a process called photorespiration.

The glyoxylic acid may give rise to succinic 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 possess enzymes for all these metabolic processes.

(ii) Glyoxysomes:

These micro bodies were discovered by Beevers (1961), and studied by Briedenbach in 1967. They are very small spherical bodies with single unit membrane found only in plants (Fig. 3.36). They contain enzymes for glyoxylate pathway. They are found in abundance in the cells of germinating oil seeds and some fungi, β-oxidation of fatty acids produces acetyl CoA, which is metabolised in glyoxylate cycle to produce carbohydrates. It also helps in conversion of stored lipid in germination oil seeds into glucose called gluconeogenesis.