Why do antibiotics target prokaryotic cells but not eukaryotic cells?

Sourav PanNovember 8, 2024

Answered

Antibiotics are designed to target prokaryotic cells, particularly bacteria, while sparing eukaryotic cells, such as those in humans and other animals. This selectivity is primarily due to fundamental differences in cellular structure and function between prokaryotes and eukaryotes.

Key Differences

Ribosomal Structure

• Ribosome Size: Prokaryotic ribosomes are classified as 70S, composed of a 50S and a 30S subunit, whereas eukaryotic ribosomes are 80S, made up of a 60S and a 40S subunit. This difference allows antibiotics to selectively inhibit bacterial protein synthesis without affecting eukaryotic ribosomes.
• Mechanism of Action: Many antibiotics, such as aminoglycosides and macrolides, specifically bind to the bacterial ribosomal subunits. This binding disrupts the translation process, leading to the production of faulty proteins or halting protein synthesis altogether.

Cell Wall Composition

• Presence of Peptidoglycan: Prokaryotic cells have a rigid cell wall composed of peptidoglycan, which is not found in eukaryotic cells. Antibiotics like penicillin target the enzymes involved in peptidoglycan synthesis, leading to cell lysis and death in bacteria. Eukaryotic cells may have cell walls (like plants with cellulose), but they lack peptidoglycan.

Differences in Metabolic Pathways

• Unique Enzymatic Targets: Some antibiotics target specific metabolic pathways that are unique to bacteria. For example, sulfonamides inhibit folic acid synthesis, a pathway that is essential for bacterial growth but absent in human cells.

Nucleic Acid Synthesis

• Selective Inhibition: Certain antibiotics target prokaryotic DNA or RNA polymerases, thereby inhibiting nucleic acid synthesis. For instance, rifamycins specifically inhibit bacterial RNA polymerase without affecting the eukaryotic counterpart