Q.Explain the structure of T-even bacteriophages.

T-even bacteriophages (e.g., T2, T4, T6 that infect E. coli) have a complex structure comprising a DNA-filled polyhedral head, a contractile tail with a central core, a base plate, and tail fibres for host attachment.

T-even bacteriophages (T2, T4, T6) are complex viruses that infect the bacterium Escherichia coli. Their structure consists of the following distinct parts:

1. Head (Capsid): An icosahedral (20-faced polyhedral), elongated protein capsid that encloses the viral genome — double-stranded DNA (dsDNA) — tightly packed inside.

2. Collar: A narrow neck-like region connecting the head to the tail, helping anchor the tail assembly to the head.

3. Tail: A hollow, cylindrical structure consisting of:

   • A central core (tail tube) — a hollow tube through which the viral DNA is injected into the host cell during infection.
   • A contractile sheath surrounding the core — this sheath can contract, driving the central core like a syringe needle through the bacterial cell wall to inject the DNA.

4. Base plate: A hexagonal (six-sided) plate located at the distal (far) end of the tail, to which the tail fibres and tail pins/spikes are attached; it plays a key role in recognizing and firmly attaching to the host cell surface.

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