Transcript PLAY
TORTORA FUNKE CASE
ninth edition
MICROBIOLOGY
an introduction
8
Part B
Microbial
Genetics
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.2
Translation
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.8
Translation
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.10
Regulation of Bacterial Gene Expression
Constitutive enzymes are expressed at a fixed rate.
Other enzymes are expressed only as needed.
Repressible enzymes
Inducible enzymes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Operon
PLAY
Animation: Operons
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.12, step 1
Regulation of Gene Expression
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.13
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Mutation
Base substitution (point
Change in one base
mutation)
Missense mutation
Result in change in
amino acid
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.16a–b
Mutation
Nonsense mutation
Results in a nonsense
codon
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.16a, c
Mutation
Frameshift mutation
Insertion or deletion of
one or more nucleotide
pairs
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.16a, d
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.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Mutation
UV radiation causes
thymine dimers.
Light-repair
separates thymine
dimers.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.19
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.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Transformation
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.23
Recombination
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.24
Conjugation
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.26a
Conjugation
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.26b
Conjugation
PLAY
Animation: Bacterial Conjugation
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.26c
Transduction
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.27
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
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Plasmids
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 8.28
Sensitive
to DNase?
a.
b.
c.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
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.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings