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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.
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