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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