Q.80 Which of the following is/are non–membrane bound inclusion bodies?
(A) Carboxysomes
(B) Cyanophycin granules
(C) Poly–β–hydroxybutyrate granules
(D) Polyphosphate granules
The correct answer is (B), (C), and (D). Carboxysomes (A) are membrane-bound (protein shell-enclosed), while cyanophycin granules, poly-β-hydroxybutyrate granules, and polyphosphate granules are non-membrane bound inclusion bodies found free in prokaryotic cytoplasm.
Option Analysis
Carboxysomes (A): These are bacterial microcompartments with a selectively permeable protein shell encapsulating Rubisco for CO2 fixation, distinguishing them from typical non-membrane bound inclusions.
Cyanophycin granules (B): Composed of arginine-aspartic acid copolymers, these nitrogen storage granules lie free in cyanobacterial cytoplasm without any membrane enclosure.
Poly-β-hydroxybutyrate (PHB) granules (C): Lipid-based carbon/energy reserves in bacteria like Azotobacter, these granules exist as cytoplasmic inclusions lacking a bounding membrane.
Polyphosphate granules (D): Also called volutin granules, these phosphate storage bodies appear as non-membranous metachromatic granules in bacterial cytoplasm.
Non-membrane bound inclusion bodies serve as essential cytoplasmic storage structures in prokaryotes, enabling nutrient reserves without lipid bilayer enclosure. These granules support survival under nutrient stress, a key topic for CSIR NET life sciences aspirants studying bacterial cell biology.
Key Types
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Cyanophycin granules: Nitrogen reserves in cyanobacteria, made of equimolar arginine-aspartic acid polypeptides, appearing granular in electron micrographs without membranes.
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Poly-β-hydroxybutyrate (PHB) granules: Carbon storage lipids in diverse bacteria, surrounded by phasins but lacking true membranes, visible via Nile red staining.
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Polyphosphate granules: Volutin/metachromatic granules storing phosphate for energy/nucleic acid synthesis, staining red with methylene blue, free in cytoplasm.
Comparison Table
| Inclusion Body | Composition | Function | Membrane Status |
|---|---|---|---|
| Carboxysomes | Rubisco + protein shell | CO2 fixation | Protein shell (not non-membrane bound) |
| Cyanophycin granules | Arginine-aspartate polymer | N storage | Non-membrane bound |
| PHB granules | Hydroxybutyrate polymer | C/energy reserve | Non-membrane bound |
| Polyphosphate granules | PolyP chains | P/energy storage | Non-membrane bound |
Carboxysomes differ due to their functional protein shell, while the others exemplify true non-membrane bound inclusion bodies per NCERT prokaryotic cell descriptions. This distinction appears frequently in competitive exams testing inclusion body classification.
