The presence of in the bacterial cell wall is one of the mechanisms of antibiotic selective toxicity.

Peptidoglycan

Explanation:

Peptidoglycan (murein) consists of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria. Peptidoglycan  is a unique and essential structural component in the cell wall of most bacteria, and it is used stimulates innate immune responses. Peptidoglycan determines the cell form and provides rigidity to the cell wall.

Peptidoglycan is an excellent target for antibiotics because it protects the bacteria cell wall.

i thinking chemical change

allowed for the prediction of the properties of missing elements.