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Difficulty: MediumViruses: Structure and Characteristics

When purified and isolated outside a host organism, viral particles can form crystals and exhibit no measurable respiration or energy production. Which of the following features explains why viruses are metabolically inert outside a host cell?

  1. The complete absence of cytoplasm, cell organelles, and metabolic machineryAnswer
  2. B
    The presence of a thick peptidoglycan cell wall that prevents metabolic exchange
  3. C
    The possession of membrane-bound mitochondria that remain dormant in extracellular fluid
  4. D
    The presence of cytoplasmic ribosomes that only function under aerobic conditions

Answer

The complete absence of cytoplasm, cell organelles, and metabolic machinery accounts for the metabolic inactivity of extracellular viruses.
The correct option states that viruses lack cytoplasm, cellular organelles, and metabolic machinery. Because viruses are acellular nucleoprotein particles without cytosol, enzymes for cellular respiration, or organelle systems, they cannot synthesize ATP or perform metabolic work when isolated from host cells.

Step-by-Step Solution

1
Analyze the structural nature of viruses
Viruses are classified as acellular (non-cellular) nucleoprotein particles.
Understanding whether viruses possess cellular organelles determines their metabolic capabilities.
2
Evaluate viral components required for metabolism
Viruses possess only a nucleic acid core (DNA or RNA) surrounded by a protein coat (capsid), lacking cytoplasm, enzymes, and ATP-generating machinery.
Metabolism requires cytosol, cellular organelles, and functional metabolic pathways.
3
Deduce extracellular behavior from structural composition
Without cellular machinery, viruses cannot generate energy or perform metabolic functions outside a living host cell, functioning as obligate intracellular parasites.
Connects viral acellular structure to extracellular metabolic inertness.

Key Concept

Acellular Nature and Obligate Intracellular Parasitism of Viruses
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Topics

Viruses: Structure and Characteristics

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