MICROBODIES: Definition, Types, Examples, Diagram, Functions

What are Microbodies?

Microbodies are small membrane-bounded organelles in eukaryotic cells, associated with metabolic processes, including detoxification, fatty acid oxidation, and hydrogen peroxide breakdown. They were first identified by Christian de Duve in the 1950s when he defined peroxisomes and later glyoxysomes and further elaborated on the importance of these organelles in cellular metabolism and defence.

Structure of Microbodies

The structure of microbodies include:

Single Membrane Organization

They are small, spherical organelles that are bounded by a single membrane of a lipid bilayer, which maintains the special environment within the microbodies. The membrane consists of phospholipids plus proteins that enable the free transfer of both metabolites and enzymes into and out of the microbody.

Enzymes (Catalase, Oxidases)

The microbody contains various enzymes, like catalase and oxidases that are contained in the peroxisomes. These enzymes are equipped to carry out important metabolic functions, which encompass the oxidation of fatty acids, detoxification, and conversion of carbohydrates.

Types of Microbodies

Microbodies are mainly divided into two types:

Peroxisomes

These microbodies contain enzymes for peroxide biosynthesis. These are present in both the plant cells and animal cells in close proximity to ER, mitochondria and chloroplasts. In the presence of molecular oxygen, hydrogen peroxide is metabolised by the catalase enzyme.

The following enzymes are present in the peroxisomes:

1. Urate oxidase

2. D-amino acid oxidase

3. Α-hydroxy acid oxidase

4. Β- hydroxy acid oxidase

Glyoxysomes

These are specialised single membrane-bound microbodies found in plants (particularly in fat-storing tissues) and filamentous fungi. The key enzymes of the glyoxylate cycle - isocitrate lyase and malate synthase are present in the glyoxysomes.

They are responsible for the breakdown of fatty acids and their conversion into sugars through gluconeogenesis. They are believed to be special types of peroxisomes.

Functions of Microbodies

The functions of microbes are:

Fatty Acid Metabolism

Peroxisomes are mainly concerned with fatty acid metabolism. They carry out oxidation reactions that result in the formation of hydrogen peroxide.

Detoxification

This hydrogen peroxide is used to detoxify the toxic compounds. Peroxisomes in the liver help in the detoxification of alcohol.

Conversion of Lipids to Carbohydrates

In plants, microbodies such as peroxisomes and glyoxysomes play a vital role during seed germination. Peroxisomes help in the breakdown of fatty acids, while glyoxysomes carry out the glyoxylate cycle, converting stored lipids into carbohydrates which act as a source of energy for the growing seed.

Photorespiration in Plants

In plants, peroxisomes play a key role in photorespiration. They help to recycle phosphoglycolate formed during photosynthesis. This is important as if the recycling did not occur the majority of the cell’s energy and carbon would be lost.

Biogenesis of Microbodies

The biogenesis of microbodies is discussed below:

Origin from ER and Golgi Apparatus

Microbodies are known to originate in and develop within the cell through vesicles budding off from the endoplasmic reticulum (ER). The ER is the source of membrane as well as the enzymes. Further maturation, with the help of the Golgi apparatus, and sorting of the enzymes is also done with the assistance provided in this process.

Genetic Regulation

Genetic factors have been elucidated as a factor for microbody participation. Certain genes encode the proteins and enzymes essential for carrying out the functions of microbodies. These properly functioning genes should then be responsible for the correct assembly, targeting enzymes, and proper regulation of microbodies within the cell.

Microbodies in Different Organisms

The microbodies are present in different organisms and perform different functions.

Plants

• Peroxisomes take part in photorespiration and aid in the removal of hydrogen peroxide.

• Glyoxysomes are primary in the conversion of the lipid bodies stored by the plants. This is a further conversion of the lipid bodies into carbohydrate form.

Animals

• Peroxisomes are the major types of microbodies in animal cells.

• They are therefore crucial for lipid breakdown and detoxification of the body from toxic hydrogen peroxide.

Fungi

• Peroxisomes make up most of the microbodies in the fungi.

• These are involved in a variety of metabolic functions similar to beta-oxidation of fatty acids to detoxification of reactive oxygen species.

Clinical and Biotechnological Significance

Microbodies have important roles in human health and biotechnology. Any dysfunction can cause diseases and the enzymes are used in industrial and medical research.

• Microbodies are kept at the core of human health. Some of the fatal metabolic complications are linked with peroxisomal disorders due to the non-functionality of microbodies.

• Microbodies are exploited for their enzymatic activities such as biofuels and bioplastics production.

• Recent research related to the action of gene therapy and the induced engineering of microbodies to enhance their metabolic capabilities for their applications in therapeutics and industry is ongoing.

Microbodies NEET MCQs (With Answers & Explanations)

Important topics for NEET exam are:

• Types of Microbodies (Peroxisomes, Glyoxysomes)

• Functions of Microbodies

• Microbodies in different organisms

Practice Questions for NEET

Q1. Microbodies containing enzymes for peroxide biosynthesis are

1. Peroxisomes and glyoxysomes

2. Peroxisomes and Golgi bodies

3. Peroxisomes only

4. Glyoxysomes only

Correct answer: 3) Peroxisomes only

Explanation:

Microbodies are small, single membrane-bound organelles that take part in the absorption of molecular oxygen and oxidation. Peroxisomes are a type of microbody that contains enzymes for peroxide biosynthesis. They are present in both plant and animal cells, near the endoplasmic reticulum, mitochondria, and chloroplasts. The key enzymes include urate oxidase, D-amino acid oxidase, α-hydroxy acid oxidase, and β-hydroxy acid oxidase. They produce hydrogen peroxide, which is metabolized by catalase to detoxify harmful substances.

Hence, the correct answer is option 3) Peroxisomes only.

Q2. Which one of the following is not considered as a part of the endomembrane system?

1. Golgi complex

2. Peroxisome

3. Vacuole

4. Lysosome

2) Peroxisome

Explanation:

Cell organelles, whose functions are coordinated, are considered together as an endomembrane system. The endomembrane system includes the endoplasmic reticulum (ER), Golgi complex, lysosomes, and vacuoles. Since the functions of the mitochondria, chloroplast, and peroxisomes are not coordinated with the above components, these are not considered part of the endomembrane system.

Hence, the correct answer is option 2) Peroxisome.

Q3. Which of the following is a function of peroxisomes?

1. Recycling phosphoglycolate

2. Mobilization of fatty acids during the seed germination

3. Detoxification of alcohol

4. All of these

Correct answer: 4) All of these

Explanation:

Membrane-bound organelles called peroxisomes are vital to the cell for several reasons.

• Phosphoglycolate recycling: As a byproduct of the Calvin cycle, phosphoglycolate is recycled by peroxisomes during photorespiration in plants.

• Fatty acid mobilization during seed germination: Peroxisomes particularly in plants use β-oxidation to break down fatty acids and generate energy during seed germination.

• Alcohol detoxification: Using enzymes like catalase, and peroxisomes in liver cells helps in the detoxification of alcohol by converting toxic chemicals including alcohol into less dangerous molecules.

Hence, the correct answer is option 4)All of these.

Also Read:

• MCQs on Microbodies

• Cytoplasm

• Cell wall

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