Transcript Document
TORTORA FUNKE CASE
ninth edition
MICROBIOLOGY
an introduction
8
Part C
Microbial
Genetics
PowerPoint® Lecture Slide Presentation prepared by Christine L. Case
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Mutation
A change in the genetic material
Mutations may be neutral, beneficial, or harmful.
Mutagen: Agent that causes mutations
Spontaneous mutations: Occur in the absence of a
mutagen
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Mutation
Base substitution (point mutation) - Change in one base
Can be a missense or nonsense mutation.
Missense mutation - Result in change in amino acid
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Figure 8.16a–b
Mutation
Nonsense mutation - Results in a nonsense codon
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Figure 8.16a, c
Mutation
Frameshift mutation - Insertion or deletion of one
or more nucleotide pairs
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Figure 8.16a, d
Mutation
Ionizing radiation (X rays and gamma rays) causes
the formation of ions that can react with nucleotides
and the deoxyribose-phosphate backbone.
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Mutation
UV radiation causes
thymine dimers.
Light-repair enzymes
separate thymine
dimers.
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Figure 8.19
The Frequency of Mutation
Spontaneous mutation rate = 1 in 109 replicated base
pairs or 1 in 106 replicated genes
Mutagens increase to 10–5 to 10–3 per replicated gene.
10 to 1000 more times likely to occur
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Selection
Positive (direct) selection detects mutant cells
because they grow or appear different.
Ex. Looking for penicillin resistance on penicillin
containing agar
Negative (indirect) selection detects mutant cells
because they do not grow.
Use of replica plating can be used for ID
PLAY
Animation: Mutations and DNA Repair
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Replica Plating
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Figure 8.20
The Ames Test for Chemical Carcinogens
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Figure 8.21
Genetic Transfer and Recombination
Vertical gene transfer: Occurs during
reproduction between generations of cells.
Parent to offspring
Horizontal gene transfer: The transfer of
genes between cells of the same generation.
PLAY
Animation: Horizontal Gene Transfer
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Transformation
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Figure 8.23
Recombination
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Figure 8.24
Conjugation
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Figure 8.26a
Conjugation
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Figure 8.26b
Conjugation
PLAY
Animation: Bacterial Conjugation
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Figure 8.26c
Transduction
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Figure 8.27
Plasmids
Conjugative plasmid: Carries genes for sex pili and
transfer of the plasmid (F factor plasmid in E. coli)
Dissimilation plasmids: Encode enzymes for
catabolism of unusual compounds, sometimes toxins
R (resistance) factors: Encode antibiotic resistance
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