Edexcel International A Level Biology

Revision Notes

6.13 Antibiotics

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  • When humans experience a bacterial infection they are often prescribed antibiotics 
  • Antibiotics are chemical substances that damage bacterial cells with little or no harm to human tissue
    • Penicillin is a well-known example; it was discovered in 1928 by Sir Alexander Fleming
  • Antibiotics are either  
    • Bactericidal; they kill bacterial cells
    • Bacteriostatic; they inhibit bacterial growth processes
      • Note that bacteriostatic antibiotics given at a high enough dose will result in the death of bacterial cells
  • Antibiotics work by interfering with the growth or metabolism of the target bacterium e.g.
    • Inhibiting bacterial enzymes needed to form bonds in the cell walls; this prevents bacterial growth and can cause death
      • Cell walls are weakened and burst under the pressure of water entering the cell by osmosis
    • Binding to ribosomes and preventing protein synthesis; this inhibits enzyme production, stopping metabolic processes in the bacterial cell
    • Damaging cell membranes, leading to loss of useful metabolites or uncontrolled entry of water
    • Preventing bacterial DNA from coiling into rings, meaning that it no longer fits into the bacterial cell
  • Since mammalian cells are eukaryotic, they will not be damaged by antibiotics
    • They do not have cell walls
    • They have different enzymes
    • They have different ribosomes
  • Viruses do not have cellular structures such as enzymes, ribosomes, and cell walls so they are not affected by antibiotics

How antibiotics work

Penicillin prevents the formation of a strong cell wall in prokaryotes, ultimately leading to the death of the cell by lysis

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Author: Marlene

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.