What is the role of penicillin-binding proteins in bacterial cell wall synthesis?

• A. They catalyze cross-linking of peptidoglycan.
• B. They synthesize RNA.
• C. They transport nutrients across membrane.
• D. They synthesize DNA.

Answer: (A)

Penicillin-binding proteins are the enzymes that perform the final stitching of the bacterial cell wall by catalyzing the cross-linking of peptidoglycan. They act as transpeptidases, linking peptide side chains between adjacent glycan strands to create a rigid, mesh-like layer. This cross-linking is essential for the wall’s strength, allowing the bacterium to resist osmotic pressure.

When penicillin binds to these proteins, it inhibits their transpeptidase activity, preventing cross-link formation. The resulting weakened wall can’t withstand internal pressure and the cell lyses. Other cellular processes are carried out by different enzymes—RNA is synthesized by RNA polymerase, DNA by DNA polymerase, and nutrients are transported across the membrane by various transport proteins—so those activities aren’t the role of penicillin-binding proteins.