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Difficulty: HardViruses: Structure and Characteristics

An infectious agent causing leaf mottling was isolated and passed through a bacterial-retaining filter. Biochemical analysis confirmed that the particle contains single-stranded RNA enclosed by capsomeres, but completely lacks cytoplasm, membrane-bound organelles, and metabolic enzymes. Which of the following statements accurately describes the biological nature of this entity?

  1. It is an acellular obligate intracellular parasite possessing only one type of nucleic acid enclosed in a protein coat.Answer
  2. B
    It is a specialized prokaryotic cell possessing cytoplasm and containing both DNA and RNA.
  3. C
    It is a unicellular organism capable of independent metabolic synthesis and binary fission outside host cells.
  4. D
    It is a microscopic saprophyte possessing a peptidoglycan cell wall and independent ATP-generating machinery.

Answer

The entity is an acellular obligate intracellular parasite consisting of a single type of nucleic acid enclosed in a protein capsid.
Viruses are non-cellular (acellular) biological entities composed of genetic material (either DNA or RNA) enclosed by a protective protein coat known as a capsid. Outside living host cells, they possess no metabolic activity and act strictly as obligate intracellular parasites.

Step-by-Step Solution

1
Analyze the structural and biochemical properties of the isolated agent.
The agent passes through bacterial filters, lacks cytoplasm, organelles, and enzymes, and contains RNA within capsomeres.
These characteristics rule out cellular organisms such as bacteria, fungi, or protists.
2
Evaluate the nucleic acid organization and host dependence against viral characteristics.
Viruses are acellular nucleoprotein complexes with a single nucleic acid type (DNA or RNA) enclosed in a protein capsid.
Lacking metabolic organelles, viruses must infect host machinery to replicate, defining them as obligate intracellular parasites.

Key Concept

Viruses are acellular entities composed of either DNA or RNA enclosed within a protein coat (capsid) and act as obligate intracellular parasites.
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Topics

Viruses: Structure and Characteristics

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