Microbodies

• These are membrane bound minute vesicles that contain various types of enzymes.
• Microbodies are of different types such as Spherosomes, peroxisomes, and glyoxysomes.
• Spherosomes and glyoxysomes are exclusively found in plants while peroxisomes are found in both plants and animals.
• Each of the microbodies is destined to perform a particular function.

Topic covered:

• Spherosomes
• Peroxisomes
• Glyoxysomes

Spherosomes :
 

Introduction:

• They are often called plant lysosomes.
• They are associated with synthesis and storage of fat.
• They are exclusively found in plant cells.

Detailed explanation:

• These are found mainly in cells involved in the synthesis and storage of fats such as the endosperm of oily seeds.
• 98% of a sphaerosome is made up of lipids whereas the remaining 2% is made up of proteins.
• Some proteins are probably enzymatic and take part in the synthesis of lipids.
• They arise from the endoplasmic reticulum and are surrounded by a single but half-unit membrane with a phospholipid monolayer having polar heads towards the cytosol and hydrophobic tails towards the inner side.
• Sphaerosomes of some tissues such as tobacco endosperm and maize root tip contain hydrolytic enzymes, hence, exhibit lysosomal activity.

Peroxisomes:
 

Introduction:

• Peroxisomes are the organelle defined by Christian de Duve in 1965.
• It was discovered with the help of a fractionation technique.
• These microbodies are found in both plant and animal cells.

Detailed explanation:

• It is found in close association with organelles like endoplasmic reticulum, mitochondria, and chloroplasts.
• It is present in all eukaryotic cells and quite abundant in the cells of the liver and kidney .
• The photosynthetic cell contains 70-100 peroxisomes and developed from the endoplasmic reticulum.
• The shape, size, and diameter of the peroxisomes are variable.
• These structures are covered with the outer membrane and the interior matrix can be granular or have evenly arranged fibrils.
• These microbodies contain oxidative enzymes such as urate oxidase, hydroxy acid oxidase, and hydroxy acid oxidase.
• Molecular oxygen is required.
• The reaction produces hydrogen peroxide which is immediately metabolized by another enzyme called catalase.

Function of peroxisomes:

• Several toxic substances in the animal cell such as nitrite, phenols, formaldehyde, formic acid, methanol, ethanol are metabolized by peroxisomes. 25% of alcohol consumed is detoxified inside liver cells.
• Xenobiotics are unusual substances that cannot be metabolized by normal enzymes but are broken down inside peroxisomes.
• Long and branched-chain fatty acids such as prostaglandins are broken down by peroxisomes.
• This organelle converts fixed nitrogen into ureids for transportation in the root nodules.
• Plant peroxisomes found in photosynthetic cells are responsible for photorespiration and are associated with the chloroplast and mitochondria.
• Peroxisomes pick up glycolate from chloroplasts which are later oxidized with the help of oxygen to produce glyoxylate. During the process hydrogen peroxide is produced as a byproduct.
• Glyoxylate is changed to amino acid glycine. The glycine then condenses to produce amino acid serine and carbon dioxide.

Glyoxysomes:
 

Introduction:

• These are the microbodies containing the enzymes for -oxidation of fatty acids along with the glyoxylate pathway.
• This was discovered by Breidenbach in 1967.
• These organelles are considered to be the special form of peroxisomes.
• These are exclusively found in the plants and are the largest microbodies.

Detailed explanation:

• Glyoxysomes are the structures that are present in the germinating fatty seeds (castor, groundnut seed, etc.) and the cells of some fungi until and unless the stored fat is consumed.
• Glyoxysomes have a single covering membrane and contain enzymes.
• -oxidation of fatty acids produces acetyl CoA.
• The latter is metabolized in the glyoxylate cycle to produce carbohydrates.
• The glyoxysomes are converted to peroxisomes after performing their function.
• These structures reappear in the senescent plant tissues for degradation of lipids and their mobilization.

Frequently Asked Questions: FAQs

Question 1. What are the main functions of the peroxisome?
Solution:

• Several toxic substances in the animal cell such as nitrite, phenols, formaldehyde, formic acid, methanol, ethanol are metabolized by peroxisomes. 25% of alcohol consumed is detoxified inside liver cells.
• Xenobiotics are unusual substances that cannot be metabolized by normal enzymes but are broken down inside peroxisomes.
• Long and branched-chain fatty acids such as prostaglandins are broken down by peroxisomes.
• This organelle converts fixed nitrogen into ureids for transportation in the root nodules.
• Plant peroxisomes found in photosynthetic cells are responsible for photorespiration and are associated with the chloroplast and mitochondria.
• Peroxisomes pick up glycolate from chloroplasts which are later oxidized with the help of oxygen to produce glyoxylate. During the process hydrogen peroxide is produced as a byproduct.
• Glyoxylate is changed to amino acid glycine. The glycine then condenses to produce amino acid serine and carbon dioxide.

Question 2. State the function of glyoxysomes?
Solution:

• Glyoxysomes have a single covering membrane and contain enzymes.
• -oxidation of fatty acids produces acetyl CoA.
• The latter is metabolized in the glyoxylate cycle to produce carbohydrates.
• The glyoxysomes are converted to peroxisomes after performing their function.
• These structures reappear in the senescent plant tissues for degradation of lipids and their mobilization used in the degradation of lipids.

Question 3. Define spherosomes ?
Solution:

• They are often called plant lysosomes.
• They are associated with synthesis and storage of fat.
• They are exclusively found in plant cells.
• These are found mainly in cells involved in the synthesis and storage of fats such as the endosperm of oily seeds.
• 98% of a sphaerosome is made up of lipids whereas the remaining 2% is made up of proteins.
• Some proteins are probably enzymatic and take part in the synthesis of lipids.
• They arise from the endoplasmic reticulum and are surrounded by a single but half-unit membrane with a phospholipid monolayer having polar heads towards the cytosol and hydrophobic tails towards the inner side.
• Sphaerosomes of some tissues such as tobacco endosperm and maize root tip contain hydrolytic enzymes, hence, exhibit lysosomal activity.

Question 4. Name the microbodies found in plant cells.
Solution:

• Peroxisomes and glyoxysomes are the two major types of microbodies found in plant cells.

Question 5. Which microbody is referred to as specialized peroxisomes?
Solution:

• Glyoxysomes are the structures that are present in the germinating fatty seeds (castor, groundnut seed, etc.) and the cells of some fungi until and unless the stored fat is consumed.
• -oxidation of fatty acids produces acetyl CoA.
• The latter is metabolized in the glyoxylate cycle to produce carbohydrates.
• The glyoxysomes are converted to peroxisomes after performing their function.Hence often called as specialized peroxisomes.
• These structures reappear in the senescent plant tissues for degradation of lipids and its mobilization.

Question 6. What role does peroxisomes play in plants?
Solution:

• Plant peroxisomes found in photosynthetic cells are responsible for photorespiration and are associated with the chloroplast and mitochondria.
• Peroxisomes pick up glycolate from chloroplasts which are later oxidized with the help of oxygen to produce glyoxylate. During the process hydrogen peroxide is produced as a byproduct.
• Glyoxylate is changed to amino acid glycine. The glycine then condenses to produce amino acid serine and carbon dioxide.