biotech 2011-04-prokaryotic-expression
TRANSCRIPT
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M I C R O B I O L O G Ya n i n t r o d u c t i o n
ninth edition TORTORA FUNKE CASE
Part B8Microbial Genetics
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Translation
mRNA is translated in
codons (three nucleotides)
Translation of mRNA
begins at the start codon:
AUG
Translation ends at a stop
codon: UAA, UAG, UGA
PLAY Animation: Translation
Figure 8.2
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Translation
Figure 8.8
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Translation
Figure 8.10
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Regulation of Bacterial Gene Expression
Constitutive enzymes are expressed at a fixed rate.
Other enzymes are expressed only as needed.
Repressible enzymes
Inducible enzymes
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Operon
PLAY Animation: Operons
Figure 8.12, step 1
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Regulation of Gene Expression
Figure 8.13
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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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Base substitution (point
mutation)
Missense mutation
Mutation
Change in one base
Result in change in
amino acid
Figure 8.16a–b
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Nonsense mutation
Mutation
Results in a nonsense
codon
Figure 8.16a, c
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Mutation
Frameshift mutation Insertion or deletion of
one or more nucleotide
pairs
Figure 8.16a, d
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Mutation
Ionizing radiation (X rays and gamma rays) causes the
formation of ions that can react with nucleotides and
the deoxyribose-phosphate backbone.
Nucleotide excision repairs mutations.
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Mutation
UV radiation causes
thymine dimers.
Light-repair
separates thymine
dimers.
Figure 8.19
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The Frequency of Mutation
Spontaneous mutation rate = 1 in 109 replicated base
pairs or 1 in 106 replicated genes
Mutagens increase to 10–5 or 10–3 per replicated gene.
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Selection
Positive (direct) selection detects mutant cells because
they grow or appear different.
Negative (indirect) selection detects mutant cells
because they do not grow.
PLAY Animation: Mutations and DNA Repair
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Genetic Transfer and Recombination
Vertical gene transfer: Occurs during
reproduction between generations of cells.
Horizontal gene transfer: The transfer of genes
between cells of the same generation.
PLAY Animation: Horizontal Gene Transfer
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Transformation
Figure 8.23
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Recombination
Figure 8.24
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Conjugation
Figure 8.26a
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Conjugation
Figure 8.26b
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Conjugation
PLAY Animation: Bacterial Conjugation
Figure 8.26c
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Transduction
Figure 8.27
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Plasmids
Conjugative plasmid: Carries genes for sex pili and
transfer of the plasmid
Dissimilation plasmids: Encode enzymes for catabolism
of unusual compounds
R factors: Encode antibiotic resistance
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Plasmids
Figure 8.28
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Sensitive to DNase?
a.
b.
c.
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You have isolated a strain of E. coli that is resistant to penicillin, streptomycin, chloramphenicol, and tetracycline. You also observe that when you mix this strain with cells of E. coli that are sensitive to the four antibiotics, they become resistant to streptomycin, penicillin and chloramphenicol, but remain sensitive to tetracycline. Explain what is going on.