Antibiotics (DP IB Biology)

Antibiotics

• Antibiotics are drugs that inhibit the growth of microorganisms

  • Most antibiotics kill or stop the growth of bacteria (prokaryotes) but do not harm the cells of the infected organism

  • This is because they block specific processes that occur in prokaryotic cells but do not have the same effect on eukaryotic cells

• Processes that might be targeted include:

  • Transcription

  • Translation

  • DNA replication

  • Ribosome function

  • Cell wall formation

• Some antibiotics are derived from living organisms such as saprotrophic fungi

  • Penicillin is produced by certain fungi in the genus Penicillium

  • When growing in the wild the antimicrobial secretions of the fungus helps it to compete by killing nearby saprotrophic bacteria

• Antibiotics can also be made synthetically (in a laboratory)

Antibiotic action diagram

Penicillin interferes with the production of bacterial cell walls

• Penicillin is not effective against all bacteria (e.g. tuberculosis) because the bacteria may have:

  • Thicker cell walls which reduce permeability

  • Enzymes which breakdown penicillin

• There are many different examples of antibiotics which are effective against a range of bacterial diseases

Antibiotics & viruses

• Antibiotics are ineffective against viruses as they are non-living

• Viruses are particles and not cells

  • They have no metabolism or cell structure and therefore cannot be targeted in any of the ways that antibiotics target a bacterial cell

• When a virus replicates, it uses the host cell’s mechanisms for transcription, translation and other metabolic pathways, so not even these processes can be targeted as antibiotics do not bind to the proteins that host cells use in these processes

  • Drugs that would target these processes would damage the host cells and cause even more harm

• Antivirals are drugs that target viral enzymes without harming the host cell