What does penicillin do in the body?

Answer 1

Penicillin is an antibiotic that destroys Bacteria by destroying the cell wall of the microorganism. It does this by inactivating an enzyme necessary for the cross linking of bacterial cell walls. The enzyme is known as transpeptidase. It accepts the penicillin as a substrate, it then alkanolates nucleophilic oxygen of the enzyme, rendering it inactive. Cell wall construction stops and the bacteria soon die. The antibiotic nature of the penicillin is due to the strained b-lactam ring, on opening the ring strain is relieved this makes penicillin more reactive than ordinary amides

Penicillin operates by dissolving the cell wall of bacteria, dispersing its cytoplasm and other cell systems. One essential component of the bacterial cell wall is transpeptidase, which accepts molecules of penicillin as a substrate attachment. The penicillin activates, preventing peptidoglycan reactions that strengthen links in the cell wall. This leads inevitably to cytolysis and cell death.

Answer 2

killing bacteria by penicillin

It kills only gram-positive bacteria by disrupting the crosslinking of peptidoglycan in the cell wall. When the peptidoglycan is not crosslinked, it is semi-liquid and can not contain the high osmotic pressure inside the bacterial cell. So the cells burst.

Note: most bacteria are gram-negative. They usually don't need (and often don't have) peptidoglycan to survive. So penicillin doesn't really affect them.

Answer 3

Except for people that are allergic to penicillin the only thing it does is kill bacteria. However penicillin (and other antibiotics) does not distinguish between harmful disease causing bacteria and helpful symbiotic bacteria (e.g. intestinal bacteria that help with digestion, harmless bacteria in the mouth that block harmful bacteria or fungi from finding places to grow) which often causes you to get sick unless you replace the missing harmless bacteria by taking probiotics as soon as you stop the penicillin.

People that are allergic to penicillin can have unpleasant or even fatal reactions when they take penicillin, but this is what their own immune system does to them, not what the penicillin did to them directly.