Q.Explain the structure of T-even bacteriophages.

T-even bacteriophages (e.g., T2, T4) have a complex structure with a DNA-filled head, a contractile tail with a sheath and core, and a base plate bearing tail fibres for host attachment.

T-even bacteriophages (T2, T4, T6) are DNA viruses that infect the bacterium Escherichia coli, and are structurally among the most complex known viruses. Their structure has two main parts:

1. Head (Capsid):

• Polyhedral (icosahedral, elongated) in shape.
• Made of protein subunits (capsomeres) that form the outer covering.
• Encloses the viral genetic material — double-stranded DNA, tightly packed inside.

2. Tail:

• Connected to the head via a short neck/collar.
• Consists of a hollow central core (tube) through which DNA is injected into the host, surrounded by a contractile sheath made of protein subunits that can contract during infection.
• At the distal end is a hexagonal base plate, from which project several tail fibres and tail pins/spikes.

Function tied to structure:

• The tail fibres recognise and specifically attach to receptor sites on the host bacterial cell wall. …