microbial genetics

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

M I C R O B I O L O G Ya n i n t r o d u c t i o n

ninth edition TORTORA FUNKE CASE

Part B8Microbial Genetics


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 8.8


Translation

Figure 8.10


Regulation of Bacterial Gene Expression

Constitutive enzymes are expressed at a fixed rate.

Other enzymes are expressed only as needed.

Repressible enzymes

Inducible enzymes


Operon

PLAY Animation: Operons

Figure 8.12, step 1


Regulation of Gene Expression

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


Base substitution (point

mutation)

Missense mutation

Mutation

Change in one base

Result in change in

amino acid

Figure 8.16a–b


Nonsense mutation

Mutation

Results in a nonsense

codon

Figure 8.16a, c


Mutation

Frameshift mutation Insertion or deletion of

one or more nucleotide

pairs

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.


Mutation

UV radiation causes

thymine dimers.

Light-repair

separates thymine

dimers.

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.


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


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


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


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.

microbial genetics

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