Short answers, pulled from the story.
Alexander Fleming discovered penicillin on the 3rd of September 1928 while observing a fungal contamination that killed surrounding bacteria in a petri dish at St. Mary's Hospital in London.
Howard Florey and Ernst Chain led the research team at the University of Oxford that successfully made concentrated penicillin from fungal culture broth in 1940.
The key structural feature of penicillins is the four-membered beta-lactam ring fused to a five-membered thiazolidine ring, which makes the beta-lactam ring more reactive and essential for antibacterial activity.
Penicillin kills bacteria by inhibiting the completion of peptidoglycan synthesis, which weakens the cell wall and causes water to flow uncontrollably into the cell, resulting in cell lysis and death.
Penicillin was made available to the general public in the United States on the 15th of March 1945 after mass production methods were developed during the war.
Alexander Fleming, Howard Florey, and Ernst Chain shared the 1945 Nobel Prize in Physiology or Medicine for the development of penicillin.