Transcript Document
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
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Figure 8.2
Translation
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Figure 8.10
Translation
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Figure 8.9, step 1
Translation
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Figure 8.9, step 2
Translation
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Figure 8.9, step 4
Translation
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Figure 8.9, step 6
Translation
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Figure 8.9, step 8
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
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Figure 8.12, step 1
Enzyme Induction
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Figure 8.12, step 2a
Enzyme Induction
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Figure 8.12, step 3a
Enzyme Repression
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Figure 8.12, step 2b
Enzyme Repression
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Figure 8.12, step 3b
Regulation of Gene Expression
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Figure 8.13
Mutations
A change in the DNA - 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)
Missense
mutation
Change in one
base
Result in change
in amino acid
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Mutation
Nonsense mutation
Results in a nonsense codon
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Mutation
Frameshift mutation
Insertion or deletion of one or more nucleotide
pairs
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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.
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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.
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Replica Plating
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The Ames Test for Chemical Carcinogens
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