Question

1. Neosporin® ointment contains neomycin, streptomycin, and bacitracin. Like penicillin, bacitracin inhibits peptidoglycan synthesis, but it does so using a different mechanism.

Penicillin binds to the _____ [D-Ala-D-Ala in peptidoglycan/transpeptidase(PBP2)/bactoprenol carrier molecule] and prevents cross-linking in the peptidoglycan.

Bacitracin binds to the ____ [D-Ala-D-Ala in peptidoglycan/transpeptidase(PBP2)/bactoprenol carrier molecule] and prevents transport of ______ [amino acids/nucleotide bases/NAM-NAG monomers/D-Ala-D-Ala] across the _____ [plasma/outer] membrane to the growing peptidoglycan chain.

2. Competitive inhibition describes the mechanism of action for:

a. penicillin

b. bacitracin

c. both penicillin and bacitracin

3. Explain why bacitracin and penicillin are both more toxic to bacterial cells than to human cells.

4. Neomycin and streptomycin are both aminoglycosides. Aminoglycosides .....

a. inhibit cell wall synthesis

b. inhibit protein synthesis

c. damage cell membranes

d. inhibit DNA replication

e. inhibit folic acid synthesis

Answer 1

1) Penicillin binds to the transpeptidase(PBP2) and prevents cross-linking in the peptidoglycan.

Bacitracin binds to the bactoprenol carrier molecule and prevents transport of NAM-NAG monomers across the outer membrane to the growing peptidoglycan chain.

2) penicillin

Competitive inhibition is where the inhibitor binds to the active site of the enzyme and inhibits the activity.

In this case, penicillin is binding to the transpeptidase active site and inhibiting the binding of substrate.

3) Explain why bacitracin and penicillin are both more toxic to bacterial cells than to human cells

Ans: Bacitracin and penicillin are toxic only to bacterial cells because they inhibit the peptidoglycan synthesis which is present in bacteria but not in human cells.

4) inhibit protein synthesis