Question

Ciprofloxacin, erythromycin, and acyclovir are used to treat microbial infections. Ciprofloxacin inhibits DNA gyrase. Erythromycin binds in front of the A site on the 50S subunit of a ribosome. Acyclovir is a guanine analog.

1. What steps in protein synthesis are inhibited by each drug?
2. Which drug is more effective against bacteria? Why?
3. Which drug is more effective against viruses? Why? Which drugs will have effects on the host's cells? Why?
4. Use the index to identify the disease for which acyclovir is used.
5. Why is it more effective than erythromycin for treating this disease?

Answer 1

a.

Ciprofloxacin - DNA transcription. (and also DNA replication, but that's not part of protein synthesis)

Erythromycin - mRNA translation

Acyclovir - DNA replication (viral DNA synthesis)

b.

Ciprofoxacin, because it impairs both transcription and replication.

c.

Acyclovir, because viruses have no machinery of their own (mostly) for carrying out transcription or translation.

Acyclovir, because humans have neither DNA gyrase or 50S ribosome subunit, so ciprofloxacin and erythromycin won't affect human cells..

d.

Chickenpox, HSV infections, etc.

e.

Viruses have no 50S ribosome subunit and neither do humans. Erythromycin is, hence, useless in a viral infection.