Many antibiotics selectively kill bacteria and not mammalian cells because they block the synthesis of the ___.

The correct answer is that many antibiotics selectively kill bacteria by blocking the synthesis of the cell wall. Bacterial cells have a unique structure in their cell wall composed of peptidoglycan, which is essential for maintaining the integrity and shape of the bacteria. Antibiotics such as penicillin target this specific component, preventing bacteria from forming a proper cell wall, leading to cell lysis and death.

Mammalian cells, on the other hand, do not have a cell wall; they have a flexible cell membrane made of phospholipids and proteins. This fundamental difference in cell structure is what allows antibiotics to target bacterial cells selectively without harming mammalian cells.

While some antibiotics also inhibit protein synthesis, this mechanism can affect both bacterial and mammalian cells since both types of cells have ribosomes involved in translation. Therefore, the specificity of targeting the cell wall is a critical aspect of why these antibiotics are effective against bacteria but not against mammalian cells.