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The ‘age of antibiotics’ began in the 1940s with the availability of penicillin. With an increase in antibiotic resistance is this age about to come to an end?

1. Outline how penicillin acts on bacteria and why antibiotics do not affect viruses

  • An antibiotic is a drug that kills or stops the growth of bacteria
  • Bacterial cells are made of peptidoglycans and in the bacterial cell wall, peptidoglycans are held together by cross-links that form between them 
  • Penicilin prevents the synthesis of the cross-links between the peptidoglycan polymers in the cll walss of bacteria
  • Penicilin inhibits the enzymes that build these cross links
  • This means that penicilin is only active against growing bacteria
  • Viruses do not have a cell structure
  • They only consist of a self-replicating molecule of DNA or RNA which acts as its genetic code and a protective coat of protein molecules
  • This protective coat is not made of peptides and sugars (peptidoglycans) 
  • Therefore, penicilin does not affect viruses

2. Explain in outline how bacteria become resistant to antibiotics with reference to mutation and selection

  • Antibiotic resistance can arise when there is a change in the DNA of the bacteria or mutation
  • If the dose of an antibiotic is not followed, perhaps because people stop taking the antibiotics when they feel better, then…


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