In viral chemotherapy, it is a hybrid situation. Viruses bring their own enzymes, etc, but do use host enzymes etc. Bacteria are free-living organisms that grow on their own and bacteria use different enzymes that are very specific, therefore, antibacterial therapy can be more successful.
Water can move back and forth from the cells.
Bacteria have adapted to live in all situations. Bacterial cells have plasma membranes and a very thick cell wall composed of sugars and peptides cross-linked. The first antibiotics were based on preventing cell walls from growing. Protein Synthesis Bacterial cells have slightly different protein synthesis structures from mammalian cells - different enough to be targeted and stopped. Metabolism Antibiotics are designed to be inhibitors to block enzymes necessary to bacteria.