Adaptation & Selection - Chapter 16 AQA AS Biology

Chapter 16 - AQA AS Biology 

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  • Adaptation and Selection
    • Genetic variation in bacteria
      • adaptation = organisms adjust to suit changing environments
      • Diversity in organisms due to changes in DNA
        • changing the quantity/structure of DNA of an organisms = mutation
        • recombining existing DNA of 2 individuals = sexual reproduction
          • conjugation = recombining DNA of 2 individuals
        • Vertical gene transmission = genes passed down from 1 generation to the next generation of the same species
      • mutation
        • mutation = changes in DNA that result in different characteristics
      • conjugation
    • Antibiotics
      • antibiotics = substances produced by living organisms that can destroy or inhibit the growth of microorganisms
      • how they work
        • prevent bacteria from making normal cell walls
        • inhibit synthesis + assembly of important peptide cross-linkages in bacterial cell walls
          • weakens walls - making them unable to withstand pessure
            • can't prevent water entering + so osmotic lysis occurs - killing the bacterium
        • only effective when bacteria are growing
        • viruses - different covering to bacteria, so not killed by antibiotics
      • antibiotic resistance
        • due to chance mutation = very rare
          • but so many bacteria so total no. of mutations is large
        • GENE for antibiotic resistance is passed down by VERTICAL GENE TRANSMISSION
        • ALLELE for antibiotic resistance is carried on plasmids to other species by HORIZONTAL GENE TRANSMISSION
        • certain bacteria can accumulate DNA with resistance to a range of antibiotics = 'Superbugs'
          • more use of antibiotics = greater chance mutant bacterium will gain an advantage over normal variety
    • antibiotic use & resistance
      • Antibiotic resistance + Tuberculosis
        • treatment - antibiotics taken for a long time (6-9 months)
        • initially antibiotics destroy least resistant strains of mycobacterium, patient feels better + stops taken them
          • few remaining bacteria - most likely to be resistant - they survive, multiply and spread to others
            • can interchange genes by conjugation + multiple antibiotic resistant strains of TB form
        • 'cocktail' of 3/4 antibiotics used to ensure at least 1 is effective
        • health workers - often directly observe patients to ensure completion of antibiotics
      • antibiotic resistance + MRSA
        • many carry the bacterium belonging to the genus 'Staphylococcus' in their throats
          • 'Staphylococcur aureus' -species causing minor symptoms in healthy individuals + cleared up with antibiotics
        • MRSA = methicillin-resistant staphyloccucus aureus
          • any strain of this bacterium that is resistant to 1 or more antibiotics
        • MRSA especially prevalent in hospitals
          • people in hospital tend to be older, sicker, weaker - more vulnerable to infection
          • transmission of infections - many patients live close together/ examined by doctors + nurses who have touched other patients
          • many different antibiotics used in hospitals - strains can more easily develop multiple resistance to antibiotics
  • differences in base sequence, may result in different a.a. sequence being coded for
    • different protein/no protein produced
      • if enzyme - disrupts the metabolic  pathway - production of other substances
    • mutation
      • mutation = changes in DNA that result in different characteristics
  • occurs when 1 bacterial cell transfers DNA to another
    • conjugation


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