What is a bacteriophage?

• A. A bacterium that can cause disease
• B. A virus that infects bacteria
• C. A type of plasmid
• D. A protein complex

Answer: (B)

A bacteriophage is a virus that infects bacteria. It consists of genetic material enclosed in a protein shell and often has a tail structure that recognizes and attaches to bacterial cells. Once attached, the phage injects its DNA or RNA into the bacterium and hijacks the bacterial machinery to make new viral particles, which can lead to the destruction of the host cell during a lytic cycle. Some phages can instead integrate their genome into the bacterial chromosome and remain dormant for a period (lysogenic cycle). This concept is distinct from bacteria, which are living cells that can multiply on their own; from plasmids, which are small circular DNA molecules that replicate independently of the bacterial chromosome; and from protein complexes, which are groups of proteins without their own viral genetic material.