Penicillins and Cephalosporins

Antibiotics are used to kill bacteria. Penicillin is the first antibiotic to cure bacterial infection in humans which is produced naturally by a fungus called Penicillium chrysogenum. Penicillin and the drug called Cephalosporin are produced by the fungi of same genus Cephalosporium. They are closely related in structure and function. They are effective due to their binding property to the enzyme that catalyze the formation of cross-links between individual strands within the peptidoglycan. If the cross-links are unavailable, the bacterial cell wall become weak resulting in the tearing out of cell wall which destroys the cell. Penicillin and Cephalosporin cause little side effect in human because of their specific binding property.Since, human cells lack the enzyme involve in cross-linking peptidoglycan, they are not affected by these antibiotics.
Due to the widespread use of these antibiotics, some bacterias have developed an enzyme that break these drugs making them ineffective. Hence researchers have developed molecules closely related to penicillin and Cephalosporin in structure and carry out the same function but not largely affected by these bacterias. They include methicillin, ampicillin, ceftriaxone, etc.