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Translation

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. Translation. Figure 8.10. Translation. Figure 8.9, step 1. Translation.

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Translation

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  1. 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

  2. Translation Figure 8.10

  3. Translation Figure 8.9, step 1

  4. Translation Figure 8.9, step 2

  5. Translation Figure 8.9, step 4

  6. Translation Figure 8.9, step 6

  7. Translation Figure 8.9, step 8

  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

  9. Operon PLAY Animation: Operons Figure 8.12, step 1

  10. Enzyme Induction Figure 8.12, step 2a

  11. Enzyme Induction Figure 8.12, step 3a

  12. Enzyme Repression Figure 8.12, step 2b

  13. Enzyme Repression Figure 8.12, step 3b

  14. Regulation of Gene Expression Figure 8.13

  15. 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

  16. Mutation • Base substitution (point mutation) • Missense mutation • Change in one base • Result in change in amino acid

  17. Mutation • Nonsense mutation • Results in a nonsense codon

  18. Mutation • Frameshift mutation • Insertion or deletion of one or more nucleotide pairs

  19. 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.

  20. Mutation • UV radiation causes thymine dimers. • Light-repair separates thymine dimers.

  21. 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.

  22. Selection • Positive (direct) selection detects mutant cells because they grow or appear different. • Negative (indirect) selection detects mutant cells because they do not grow.

  23. Replica Plating

  24. The Ames Test for Chemical Carcinogens

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