Question

Bacterial enzymes participate in the construction of the bacterial cell wall. Penicillin targets these enzymes and interferes with:

A. the channels in the cell's internal structure.

B. protein synthesis.

C. bacterial DNA.

D. the addition of cross-links to the cell wall.

Answer 1

Transpeptidase is an enzyme which initiates carbonyl substitution reaction which is required for cross linkage of bacterial cell wall peptidoglycan.

Bacteria are of two types on the basis of staining and cell wall formation i.e gram positive and gram negative. Gram positive bacteria are those which have thick cell wall made up of cellulose like structural sugar polymer which is covalently bounded to short peptides in layers. Peptidoglycan layer has polysaccharide portion made up of NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine).

The cell wall of the bacteria is formed completely when cross links are formed between two consecutive peptide chains attached to polysaccharides backbones. This reaction is facilitated by the enzyme transpeptidase.

The drug Penicillin binds to the active site of the enzyme transpeptidase which forms links in the peptidoglycan layer. The antibiotic irreversibly stops this enzyme by reacting with the serine of transpeptidase thus resulting in the inhibition of the cell wall formation in bacteria.

Thus the option (D) is the correct answer.