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 8.8
Translation Figure 8.10
Regulation of Bacterial Gene Expression
Constitutive enzymes are expressed at a fixed rate.
Other enzymes are expressed only as needed.
Operon PLAY Animation: Operons Figure 8.12, step 1
Regulation of Gene Expression Figure 8.13
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
Base substitution (point mutation)
Change in one base
Result in change in amino acid
Results in a nonsense codon
Figure 8.16a, c
Insertion or deletion of one or more nucleotide pairs
Figure 8.16a, d
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.
UV radiation causes thymine dimers.
Light-repair separates thymine dimers.
The Frequency of Mutation
Spontaneous mutation rate = 1 in 10 9 replicated base pairs or 1 in 10 6 replicated genes
Mutagens increase to 10 –5 or 10 –3 per replicated gene.
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
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
Transformation Figure 8.23
Recombination Figure 8.24
Conjugation Figure 8.26a
Conjugation Figure 8.26b
Conjugation PLAY Animation: Bacterial Conjugation Figure 8.26c
Transduction Figure 8.27
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
Plasmids Figure 8.28
Sensitive to DNase? a. b. c.
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.