Adaptation & Selection - Chapter 16 AQA AS Biology
Chapter 16 - AQA AS Biology
- Created by: H.N
- Created on: 01-01-13 18:53
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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
- weakens walls - making them unable to withstand pessure
- 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
- due to chance mutation = very rare
- 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
- few remaining bacteria - most likely to be resistant - they survive, multiply and spread to others
- '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
- many carry the bacterium belonging to the genus 'Staphylococcus' in their throats
- Antibiotic resistance + Tuberculosis
- Genetic variation in bacteria
- 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
- different protein/no protein produced
- occurs when 1 bacterial cell transfers DNA to another
- conjugation
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