Resources | Subject Notes | Biology
Antibiotics are a class of drugs used to treat bacterial infections. They work by targeting essential processes in bacteria, distinguishing them from viruses, which have a different structure and replication strategy.
Penicillin is a beta-lactam antibiotic. Its primary mechanism of action involves inhibiting bacterial cell wall synthesis.
Bacteria possess a rigid cell wall made of peptidoglycans, which provides structural support and protects the cell from osmotic lysis. Peptidoglycans are composed of long chains of sugars and amino acids. The synthesis of peptidoglycans is a crucial process for bacterial growth and division.
Penicillin molecules structurally resemble the D-Ala-D-Ala peptide sequence, which is a part of the peptidoglycan precursor. Penicillin acts as a competitive inhibitor of enzymes called penicillin-binding proteins (PBPs). PBPs are responsible for cross-linking the peptidoglycan chains, forming a strong and stable cell wall.
When penicillin binds to PBPs, it prevents the cross-linking process, leading to a weakened cell wall. This weakened cell wall is unable to withstand the internal osmotic pressure, causing the bacterial cell to lyse (burst).
The effectiveness of penicillin is greatest against bacteria that are actively growing and synthesizing new cell walls.
| Step | Process | Effect of Penicillin |
|---|---|---|
| 1 | Peptidoglycan precursor synthesis | Bacterial enzymes synthesize peptidoglycan precursors. |
| 2 | Binding of Penicillin to PBPs | Penicillin binds to penicillin-binding proteins (PBPs). |
| 3 | Inhibition of Cross-linking | Prevents the cross-linking of peptidoglycan chains. |
| 4 | Weakened Cell Wall | Results in a weakened and unstable bacterial cell wall. |
| 5 | Cell Lysis | The weakened cell wall cannot withstand osmotic pressure, leading to cell lysis. |
Viruses are fundamentally different from bacteria. They are not cells and do not have a cell wall or the same metabolic processes that antibiotics target.
Viruses are essentially genetic material (DNA or RNA) enclosed in a protein coat. They cannot replicate on their own and require a host cell to reproduce. Viral replication involves hijacking the host cell's machinery to produce more viral particles.
Antibiotics specifically target bacterial processes, such as cell wall synthesis, protein synthesis, or DNA replication. Viruses lack these structures and processes, making them unaffected by antibiotics.
The structure of viruses is very different from bacteria. Viruses do not have peptidoglycan, so penicillin cannot bind to any target sites on the virus.
Therefore, antibiotics are ineffective against viral infections like the common cold, influenza, or HIV. Viral infections require antiviral medications that target specific viral processes, such as viral replication or entry into host cells.