Antibiotics work by affecting things that bacterial cells have but human cells don't. ... The antibiotic penicillin works by keeping a bacterium from building a cell wall. Bacteria and human cells also differ in the structure of their cell membranes and the machinery they use to build proteins or copy DNA.
essential amino acids.
the "essential" refers to it being necessary to derive them from the foods we eat, but in fact the amino acids that the body produces are just as essential to the proper functioning and health of our bodies.