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.