Microbodies: Structure and Types
Structure of Microbodies
- Microbodies are spherical or oblate (flattened) shaped organelles.
- They are bounded by a single membrane.
- Their interior (matrix) appears amorphous or granular under an electron microscope.
- Catalase enzyme is the key identifying feature of microbodies, distinguishing them from other cell organelles.
- When treated with 3,3′-diaminobenzidine (DAB), catalase-rich areas become electron opaque, appearing as dark regions under the electron microscope.
Isolation Technique of Microbodies (from Plant Tissues)
- Gentle Grinding of Tissue: Plant tissues are gently ground to avoid disruption of delicate microbodies.
- Differential Centrifugation: The homogenate is centrifuged in steps to separate cellular components. A fraction rich in microbodies is obtained.
- Isopycnic Ultracentrifugation: The enriched microbody fraction is subjected to density gradient centrifugation using continuous or discontinuous sucrose gradient to isolate pure microbodies.
Types of Microbodies
Recent biochemical studies identify two main types of microbodies:
1. Peroxisomes
- Found in animal cells and leaves of higher plants.
- Contain enzymes like:
- Catalase
- Oxidases (e.g., D-amino oxidase, urate oxidase)
- Function:
- Oxidation of substrates → Produces H₂O₂ (hydrogen peroxide)
- H₂O₂ is broken down by catalase to water and oxygen.
- In plants, peroxisomes are associated with chloroplasts, mitochondria, and endoplasmic reticulum (ER).
- Play a vital role in photorespiration.
2. Glyoxysomes
- Occur only in plant cells.
- Found abundantly in germinating seeds that store fats as food reserves.
- Contain:
- Enzymes of glyoxylate cycle
- Catalases and oxidases
- Function:
- Convert stored fatty acids into sugars during germination.
- This is essential for providing energy and carbon skeletons for the growing seedling.
1. Microbodies are bounded by:
A) Double membrane
B) Single membrane
C) No membrane
D) Triple membrane
✅ Answer: B) Single membrane
2. Which enzyme is a characteristic marker of microbodies?
A) DNA polymerase
B) Catalase
C) Lipase
D) ATPase
✅ Answer: B) Catalase
3. Microbodies appear electron opaque after staining with:
A) Acetocarmine
B) Hematoxylin
C) 3,3′-diaminobenzidine (DAB)
D) Safranin
✅ Answer: C) 3,3′-diaminobenzidine (DAB)
4. Peroxisomes are found in:
A) Only animal cells
B) Only plant cells
C) Fungi only
D) Both plant and animal cells
✅ Answer: D) Both plant and animal cells
5. Glyoxysomes are found in:
A) Bacterial cells
B) Animal cells
C) Germinating seeds of plants
D) Fungi
✅ Answer: C) Germinating seeds of plants
6. Which of the following organelles contains enzymes of the glyoxylate cycle?
A) Peroxisomes
B) Lysosomes
C) Glyoxysomes
D) Ribosomes
✅ Answer: C) Glyoxysomes
7. The function of catalase in microbodies is to:
A) Oxidize fatty acids
B) Break down H₂O₂ into water and oxygen
C) Synthesize glucose
D) Produce energy via glycolysis
✅ Answer: B) Break down H₂O₂ into water and oxygen
8. The matrix of microbodies is:
A) Protein-free
B) Crystalline
C) Granular or amorphous
D) Filled with starch
✅ Answer: C) Granular or amorphous
9. In plant cells, peroxisomes are associated with which organelles?
A) Golgi bodies
B) Lysosomes
C) ER, mitochondria, and chloroplasts
D) Ribosomes
✅ Answer: C) ER, mitochondria, and chloroplasts
10. Glyoxysomes are especially active during:
A) Seed dormancy
B) Seed germination
C) Leaf senescence
D) Cell division
✅ Answer: B) Seed germination
11. Microbodies can be separated using:
A) Paper chromatography
B) UV radiation
C) Sucrose density gradient centrifugation
D) Gel electrophoresis
✅ Answer: C) Sucrose density gradient centrifugation
12. The oxidation of substrates in peroxisomes leads to the formation of:
A) CO₂
B) NADH
C) Hydrogen peroxide (H₂O₂)
D) Oxygen radicals
✅ Answer: C) Hydrogen peroxide (H₂O₂)
13. Which of the following enzymes is not typically found in microbodies?
A) Urate oxidase
B) Isocitrate lyase
C) ATP synthase
D) D-amino acid oxidase
✅ Answer: C) ATP synthase
14. Which cycle is associated with glyoxysomes?
A) Krebs cycle
B) Calvin cycle
C) Glycolysis
D) Glyoxylate cycle
✅ Answer: D) Glyoxylate cycle
15. Peroxisomes are absent in which of the following?
A) Plant leaves
B) Germinating seeds
C) Animal liver cells
D) Mature RBCs
✅ Answer: D) Mature RBCs
16. Which staining technique helps visualize catalase in microbodies?
A) Crystal violet
B) DAB (Diaminobenzidine)
C) Fast green
D) Iodine
✅ Answer: B) DAB (Diaminobenzidine)
17. The lipid to sugar conversion in germinating seeds occurs in:
A) Peroxisomes
B) Glyoxysomes
C) Chloroplasts
D) Mitochondria
✅ Answer: B) Glyoxysomes
18. Microbodies do not contain:
A) Membrane
B) DNA
C) Catalase
D) Matrix
✅ Answer: B) DNA
19. The glyoxylate cycle bypasses which steps of the Krebs cycle?
A) Oxidation of acetyl CoA
B) Decarboxylation steps
C) Conversion of pyruvate to acetyl CoA
D) Electron transport
✅ Answer: B) Decarboxylation steps
20. Which of the following is used to isolate microbodies?
A) Freeze-thaw method
B) Differential centrifugation
C) Dialysis
D) Immunoprecipitation
✅ Answer: B) Differential centrifugation