How does the DNA of a bacteriophage typically enter a bacterial host cell?

• A. The DNA is transferred through pili during conjugation.
• B. The bacteriophage fuses with the bacterial membrane, releasing its DNA into the cytoplasm.
• C. The entire bacteriophage is engulfed by the bacterium via endocytosis.
• D. The bacteriophage injects its DNA directly through the bacterial cell wall and membrane.

Answer: (D)

Verified step by step guidance

1. Understand the structure of a bacteriophage: it typically has a head containing DNA and a tail structure used for attachment to the bacterial cell.
2. Recognize that bacteriophages do not enter the bacterial cell by engulfment or fusion, as bacteria lack the mechanisms for endocytosis and membrane fusion like eukaryotic cells.
3. Recall that conjugation involves transfer of DNA through pili between bacteria, not bacteriophages, so DNA transfer via pili is not applicable here.
4. Focus on the mechanism of DNA entry: the bacteriophage attaches to the bacterial surface using its tail fibers, then contracts its tail sheath to inject DNA through the bacterial cell wall and membrane.
5. Summarize that the bacteriophage injects its DNA directly into the bacterial cytoplasm, leaving the protein coat outside the cell.