Antibiotics

There are different structures of antibiotics. Groups of antibiotics can have the same basic structure, with minor differences, such as the presence of different chemical groups protruding off of the main core structure. The different groups of antibiotics are known as classes.

Penicillin is in a class known as beta-lactam antibiotics. The name of this class is based on the beta-lactam ring that forms the core of the antibiotic molecule. Tetracyclines, aminoglycosides, rifamycins, quinolones, and sulphonamides are other classes of antibiotics.

Penicillin culture. Custom Medical Stock Photo, Inc. Reproduced by permission.

The mode of action of the different classes of antibiotics is varied. For example, beta-lactam antibiotics destroy the assembly of a bacterial structure called the peptidoglycan. The peptidoglycan is a rigid net that encircles the bacterial cell. It acts as the main stress-bearing layer of the bacterial cell wall. When the assembly of the peptidoglycan is disrupted, the ability of peptidoglycan to hold the bacterial wall together vanishes, and the cell explodes. Another class of antibiotics called aminoglycosides has a different method of killing bacteria. These antibiotics bind to a section of the bacterial structure called the ribosome. The ribosome is involved in making protein. By blocking the function of the ribosome, new protein cannot be made and the bacterial cell dies. Some aminoglycoside antibiotics also reduce the ease by which molecules can move from the outside of the cell to the inside of the cell. Once again, the result is death. In another example, the class of antibiotics known as quinolones act to disrupt an enzyme that unwinds the coiled double helix of deoxyribonucleic acid. If the DNA cannot unwind, new copies cannot be made. Without new DNA, the growth and division of the bacteria stops.