Chapter 8 Microbial Genetics Flashcards

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1
Q

Two Methods of Genetic Change in Bacteria

A

1) Mutation

2) Horizontal Gene Transfer

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2
Q

Mutation

A
  • A change in the nucleotide sequence of DNA

- May cause a change in a protein encoded by a gene

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3
Q

Horizontal Gene Transfer

A

Genetic info is passed from one living cell to another cell of the same generation
Example: Plasmid Transfer

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4
Q

Base Substitution/ Point Mutation (Mutation)

A
  • A single nucleotide is replaced by another nucleotide
  • When DNA replicates - results in a substituted base pair
  • When DNA is transcribed and translated can result in an incorrect amino acid in the protein - Missense mutation
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5
Q

Frameshift Mutation (Mutation)

A
  • Insertion - one or two nucleotide(s) added to the gene
  • Deletion - one or two nucleotides removed from the gene
  • Changes the reading frame of the mRNA
  • Sequence of amino acids is changed “downstream” of mutation site
  • Almost always results in a non-functional protein
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6
Q

Spontaneous Mutation (How mutations occur)

A

Occur in absence of mutagens, due to occasional mistakes during DNA replication

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7
Q

Induced Mutation (How mutations occur)

A

Occur when DNA damaging agents cause changes in DNA sequence - mutagens
-Example: Radiation, some chemicals

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8
Q

Regardless of Origin, Mutations can result in

A

1) No effect on the protein (remains functional) - silent mutation
2) A protein with a different amino acid sequence that may have an altered function - missense mutation
3) Premature stop codon- Incomplete (truncated) protein, usually nonfunctional - nonsense mutation

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9
Q

Plasmids

A
  • Self-replicating, DNA molecules
  • Contain non-essential genes
    Example. Genes for toxin production
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10
Q

F Plasmids

A
  • Fertility Factors
  • Carry genes to make F pills (or sex pilus)
  • Involved in conjugation (transfer of genetic material between bacteria)
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11
Q

R Plasmids

A
  • Resistance Factors

- Carry genes for antibiotic resistance

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12
Q

Vir Plasmids

A
  • Virulence factors

- Carry genes for toxin production

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13
Q

Horizontal Gene Transfer in Bacteria (Basic Methods)

A

1) Transformation
2) Transduction
3) Conjugation

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14
Q

Transformation

A
  • Pieces of “naked” DNA are taken up by bacterial cells
  • ie. From dead cells, or from released plasmids
  • These pieces can be integrated into the chromosomes
    1) Recombination
    2) Can then be passed to progeny, and become a stable part of the genome
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15
Q

Transduction (Part 1)

A
  • Small fragments of DNA transferred between bacteria by bacteriophage (viruses that infect bacteria)
  • Phage attaches to bacterial cell wall - injects its DNA into the cell
  • Phage DNA is replicated inside bacterial cell
  • Phage DNA also encodes enzymes that cut the bacterium’s DNA into fragments
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16
Q

Transduction (Part 2)

A
  • As new phages are being assembled, some accidentally receive a piece of bacteria DNA instead of phage DNA –> Transducing Particle
  • The transducing particle can then carry bacterial genes to another cell
  • Injection mechanism is still fully functional
  • But, bacterial DNA is injected into the cell
  • If the injected DNA recombines with the existing chromosome it becomes a stable genetic element (i.e. Will be passed to progeny)
17
Q

Conjugation (Bacterial Mating)

A
  • Mediated by genes encoded on an F factor
  • Transfer occurs when a:
    1) Donor cell (F+) - forms an F plus and uses it to attach to a recipient cell (F-)
    2) Pilus retracts bringing the cells together
    3) The donor cell replicates the F factor as a copy is passed to the recipient
    4) The recipient becomes an F+ cell