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Working of Antibiotics

The discovery of penicillin in 1929 by Alexander Fleming ushered in a new era of
antibiotics. Many other antibiotics were soon developed that could treat diseases caused by
bacteria such as tuberculosis and pneumonia. Antibiotics are effective in treating such infections
because they are able to kill the harmful bacteria cells (prokaryotic cells) while leaving their
human host cells (eukaryotic cells) unharmed. Different antibiotics manage this feat using
different methods.
Penicillin kills some bacteria by inhibiting formation of their cell walls. Bacteria need a
macromolecule called peptidolycan for cell wall formation. This macromolecule is made by
assembling short peptides and amino sugars. Penicillin prevents the assembly of these two
materials thus preventing bacteria from making cell walls. Without cell walls, the bacterial cells
burst and die. Vancomycin also prevents peptidolycan from forming. However, it uses a different
method from that used by penicillin. Penicillin and vancomycin manage to harm bacteria cells
and not human cells because there is no human biochemical process that they interfere with
(Walsh & Wencewicz, 2016).
Tetracycline kills bacteria by inhibiting protein synthesis. Like human cells, bacteria
makes proteins on ribosomes. Tetracycline inhibits protein synthesis in bacteria by crossing its
membrane and accumulating in large numbers in the bacteria’s cytoplasm. It then binds on a
single ribosome site called 30s. It then blocks RNA interaction that is needed for protein
synthesis. The bacteria is, therefore, unable to make proteins. Tetracycline does not cause any
harm to human cells because it does not accumulate in human cells in quantities large enough to
stop synthesis of proteins as it does with bacterial cells. Chloramphemicol also works in the same

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manner except that rather than binding to 30S unit it binds to 50S unit (Walsh & Wencewicz,
2016).
Sulfonamides kills bacteria by making it hard for bacterial cells to make folic acid. It
achieves this by inhibiting the activities of dihydopteroate synthase enzyme which is needed for
bacteria to make the acid. The antibiotic does not interfere with availability of folic acid to
human cells because, unlike in bacterial cells, folic acid easily diffuses into human cells (Walsh
& Wencewicz, 2016). Thus, human cells do not need to make folic acid on their own.
Antibiotics, therefore, work by killing bacteria cells which cause diseases to human
beings. Using the various mechanisms described in this paper, they are able to kill bacteria cells
while leaving human cells unharmed. This mode of operation makes them ineffective in dealing
with viruses and diseases caused by them. Unlike bacteria, viruses grow inside human cells
(Walsh & Wencewicz, 2016). Thus, any chemical that kills them will also have to kill human
cells. This explains why antibiotics are ineffective in treating viral infections such as HIV.

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References

Walsh, C., & Wencewicz, T. (2016). Antibiotics: challenges, mechanisms, opportunities.
American Society for Microbiology (ASM).