One of the greatest achievements of the 20th century was the invention and mass production of antibiotics. Antibiotics or antimicrobials are chemical drugs used to treat a variety of different infectious bacterial diseases by destroying or slowing the growth of bacteria. Antibiotics are toxic to the target cell but do not harm the host. They are designed to attack various types of parasites, fungi and bacteria. Contrary to popular belief, antibiotics do not work against viruses like those that cause the common cold. Antibiotics are divided into different classifications because antibiotics are selective killers, meaning they are made to kill a certain strain of harmful bacteria. Each antimicrobial differs from each other in physical and chemical properties and in the spectrum of antibacterial activity. Different types of antibiotics fight the infection in different ways. The different ways the antibiotic works are by inhibiting the metabolism of the bacterial cell, preventing the synthesis of the bacterial cell wall, creating a permeable membrane of the bacterial cell, or suppressing acid transcription and replication nucleic. Most antibiotics today are semi-synthetic, meaning their natural derivative has been altered. Antibiotics have two distinct groups separated by their effect on bacteria. Bactericidal antimicrobials kill bacteria while bacteriostatic agents prevent bacteria from growing or reproducing. They are also separated based on their sector of activity. Narrow-target antibiotics target a specific group of bacteria while broad-spectrum antibiotics target many different types of cells. The first antibiotic and the best known is penicillin. It was discovered... in the middle of the paper... a. Penicillin works by inhibiting the synthesis of the bacterial cell wall. The cell wall of bacteria is made up of mucoprotiens, which is a polymer made of amino acids and sugars bonded together to form the cell wall. The chains of the polysaccharide, which is a carbohydrate covalently linked to another functional group, are linked together by a peptide cross-link. Penicillin enters the bacterial cell through the cell wall. Penicillin-binding proteins are used in bacterial cells to catalyze several reactions that ultimately lead to cell wall formation. Binding sites in normal bacterial cells are responsible for the synthesis of cross-links. Penicillin binds covalently to the activation site of the enzyme. This inactivates the binding sites causing the cell to swell with water. Eventually the cell will burst due to the influx of water molecules.