Question

Explain breifly the life cycle of T4 Bacteriphage by illustrating with a diagram.

 

Answer 1

T4 bacteriophage life cycle:

• The T4 bacteriophage is an obligatory, intracellular parasite of the bacterium Escherichia coli.
• When a Ta bacteriophage infects a bacterial cell it gets attached to the cell wall of the host's cell by its tail which secretes certain proteolytic enzymes, for making perforation in the bacterial cell wall.
• This is followed by injection of DNA core (phage chromosome) into the bacterial cell.
• The capsid of T phage remains outside the cell and called ghost. Inside the bacterial cell, the phage DNA either starts to replicate by taking the precursor substances from the host cytoplasm to form its own progeny (such a phage is called virulent phage), or becomes integrated into the host chromosome as prophage to replicate in synchrony with the bacterial chromosome (such a phage is called, non-virulent or temperate phage).
• A host cell having a virulent phage soon bursts (lyses) and releases several hundred new viral particles which can then repeat the same cycle.
• A virulent phage, thus, destroys the host cell.
• The temperate phage does not destroy bacterial cell. Very occasionally, however, a bacterium containing temperate phages will lyse and liberate several hundred infectious progeny viral particles.
• Because such hosts are potentially subject to lysis they are termed lysogenic.
• A temperate phage, thus, remains quiescent for long time, but may convert into reproductive virulent phage by some radiation source such as ultraviolet light or X-rays and disrupts the bacterial cell.

 

T4 Bacteriophage:

• Escherichia virus T4 is a species of bacteriophages which infect E.coli bacteria.
• This is a double-stranded DNA virus which belongs to subfamily Tevenvirinae of the family Myoviridae.
• This is capable of undergoing only a lytic lifecycle and not the lysogenic lifecycle.