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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