Which of the following structures represents a complex virus?

• A. A prion protein aggregate
• B. A rod-shaped viroid
• C. A bacteriophage with an icosahedral head and helical tail
• D. A spherical virus with an envelope

Answer: (C)

Verified step by step guidance

1. Understand the definition of a complex virus: Complex viruses have structures that are more intricate than simple icosahedral or helical shapes, often combining multiple structural features such as heads, tails, and additional components.
2. Review each option and identify the type of infectious agent or virus it represents: Prion protein aggregates are misfolded proteins, not viruses; viroids are small, circular RNA molecules without a protein coat; spherical viruses with envelopes are typically simple enveloped viruses.
3. Focus on the bacteriophage option: Bacteriophages often have a complex structure, including an icosahedral head that contains the genetic material and a helical tail used for attachment and injection of DNA into host bacteria.
4. Recognize that the combination of an icosahedral head and a helical tail is characteristic of complex viruses, distinguishing them from simple helical or icosahedral viruses.
5. Conclude that the bacteriophage with an icosahedral head and helical tail represents a complex virus due to its multi-part structure combining different morphological features.