Phage morphology: Which bacteriophages are described as having binal (dual) symmetry, with an icosahedral head and a helical tail?

Introduction / Context:Bacteriophages (phages) exhibit diverse morphologies. A common architecture among tailed phages is “binal symmetry,” combining two structural symmetries: an icosahedral capsid (head) attached to a helical tail apparatus for adsorption and genome injection.

Given Data / Assumptions:

• The question focuses on classic Escherichia coli T-even/T-series phages.
• “Binal” (sometimes misspelled as “banal”) refers to dual symmetry.
• We consider T2, T4, and T6 morphologies.

Concept / Approach:Tailed dsDNA phages, including T2, T4, and T6, share the canonical structure: icosahedral head containing genomic DNA and a contractile or non-contractile tail with baseplate and tail fibers. This dual-symmetry design underlies their infection mechanism: tail fibers bind receptors, the tail sheath may contract, and DNA is injected into the bacterial cytoplasm.

Step-by-Step Solution:

Verification / Alternative check:Electron micrographs and standard microbiology texts depict T-even phages as icosahedral-headed with distinctive tails and fibers.

Why Other Options Are Wrong:

• Each single-phage option is only partially correct; all three share the morphology.

Common Pitfalls:Confusing “binal” with “bilateral”; binal specifically refers to combined icosahedral and helical symmetry in phages.

Final Answer:All of these