Illustration demonstrating the infection of a bacterial cell by a bacteriophage (virus that infects bacteria) in three steps. Step 1 (top) shows the positioning of the bacteriophage (green) on the cell membrane of the bacterium. Step 2 (middle) shows the bacteriophage piercing the bacterial membrane with its syringe-like tail. Step 3 (bottom) shows the injection of the bacteriophage DNA (deoxyribonucleic acid, red scribble) into the bacterial cell where it will take control of the bacterium's cellular machinery and replicate.