Bacterial Genetics and Operons

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Bacterial Genetics and Operons
2013-07-16 15:25:21
Biology GRE

Biology GRE
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  1. Bacteria Genome
    Have a single chromosome
  2. Nucleoid
    • Regions in bacteria that contains DNA
    • Does not have a membrane
  3. Plasmids
    • Small loops of DNA that exist separate from central loop of DNA
    • Can be freely exchanged with other bacterial cells vis cytoplasmic bridges during conjugation
    • Plasmids replicate at their own rate, and can share DNA with cells while keeping the trait themselves (bacteria resistant)
  4. Genetic recombination in bacteria
    exchange DNA via free floating plasmids, and exchanging plasmids
  5. Transformation
    Bacteria pick up free floating DNA
  6. Conjugation
    Occurs between bacterial cells with cytoplasmic extensions that allows plasmids to move between cells
  7. Transduction
    • Viruses infect certain bacteria viruses
    • DNA gets incorporated into bacteria, replicates and lyses the cell, infecting new bacteria.
  8. Operon model
    • How bacteria turn DNA off and on
    • RNA polymerase attaches to promotor sequence
    • RNA polymerase reads RNA to DNA as it goes alone
    • A repressor protein can bind to operator, and stop RNA polymerase from reaching genes it needs to transcribe
    • Repressor protein can be triggered to fall off in presence of absence of a chemical.
  9. Operon
    several related genes, an operator and a promotor
  10. Operon example: Lac operon
    • Responsible for breakdown of lactose in E.coli. 
    • If RNA poly attaches to the promotor, genes needed to breakdown lactose are made
    • Repressor protein has a receptor for lactose
    • If excess lactose needs to be broken down it binds to repressor protein and protein falls off
    • i.e. Lac operon turns on when lactose is present and off when it is not present
  11. Repressible Enzymes
    • Repressor protein attaches to the operator sequence only when a certain compound is present in the environment singling the absence of the target molecule
    • Repressible usually involved with the synthesis of a substance
  12. Inducible Enzymes
    • Enzymes that can be induced or turned on by the presence of a certain substance. 
    • Inducible proteins are usually involved with the breakdown of a substance. 
    • Ex: lactose, when in the environment lac operon turns on to break it down