Microbial Genetics. Terminology Genetics Genetics Study of what genes are Study of what genes are how they carry information how they carry information.

Microbial Microbial GeneticsGenetics

TerminologyTerminology

GeneticsGenetics Study of what genes areStudy of what genes are how they carry informationhow they carry information how information is expressedhow information is expressed how genes are replicatedhow genes are replicated

GeneGene Segment of DNA that encodes a Segment of DNA that encodes a

functional product, usually a functional product, usually a proteinprotein

TerminologyTerminology

GenomeGenome All of the genetic material in a cellAll of the genetic material in a cell

GenomicsGenomics Molecular study of genomesMolecular study of genomes

GenotypeGenotype Genes of an organismGenes of an organism

PhenotypePhenotype Expression of the genesExpression of the genes

E. coliE. coli

Figure 8.1a

Polymer of nucleotides: Polymer of nucleotides: adenine, thymine, adenine, thymine, cytosine, guaninecytosine, guanine

Double helix associated Double helix associated with proteinswith proteins

"Backbone" is "Backbone" is deoxyribose-phosphatedeoxyribose-phosphate

Strands held together by Strands held together by hydrogen bonds hydrogen bonds between AT and CGbetween AT and CG

Strands are antiparallelStrands are antiparallel

DNADNA

Figure 8.4

DNADNA

Figure 8.3

DNADNA

Figure 8.5

DNA is copied by DNA polymeraseDNA is copied by DNA polymerase In the 5In the 5 3 3 direction direction Initiated by an RNA primerInitiated by an RNA primer Leading strand synthesized continuouslyLeading strand synthesized continuously Lagging strand synthesized Lagging strand synthesized

discontinuously discontinuously Okazaki fragments Okazaki fragments RNA primers are removed and Okazaki RNA primers are removed and Okazaki

fragments joined by a DNA polymerase fragments joined by a DNA polymerase and DNA ligase and DNA ligase

DNADNA

DNADNA

Figure 8.6

DNA replication is semiconservativeDNA replication is semiconservativeDNADNA

Figure 8.7

Figure 8.8

RNA processing in RNA processing in EukaryotesEukaryotes

Figure 8.12

mRNA is mRNA is translated in translated in codons (3 codons (3 nucleotides)nucleotides)

Translation of Translation of mRNA begins at mRNA begins at the start codon: the start codon: AUGAUG

Translation ends Translation ends at a STOP at a STOP codon: UAA, codon: UAA, UAG, UGAUAG, UGA

TranslationTranslation

Figure 8.2

The Genetic CodeThe Genetic Code

Figure 8.9

TranslationTranslation

Figure 8.10.1

TranslationTranslation

Figure 8.10.2

TranslationTranslation

Figure 8.10.3

TranslationTranslation

Figure 8.10.4

TranslationTranslation

Figure 8.10.5

TranslationTranslation

Figure 8.10.6

TranslationTranslation

Figure 8.10.7

TranslationTranslation

Figure 8.10.8

TranslationTranslation

Figure 8.11

Change in the genetic materialChange in the genetic material Mutations may beMutations may be

neutralneutral beneficialbeneficial or harmfulor harmful

Mutagen: Agent that causes Mutagen: Agent that causes mutationsmutations

Spontaneous mutations: Occur in the Spontaneous mutations: Occur in the absence of a mutagenabsence of a mutagen

MutationMutation

Base substitution Base substitution (point mutation)(point mutation)

Missense mutationMissense mutation

MutationMutation

Figure 8.17a, b

•Change in one Change in one basebaseResult in change in Result in change in amino acidamino acid

Nonsense Nonsense mutationmutation

MutationMutation

• Results in a Results in a nonsense codonnonsense codon

Figure 8.17a, c

Frameshift Frameshift mutationmutation

MutationMutation

Figure 8.17a, d

•Insertion or deletion of Insertion or deletion of one or more nucleotide one or more nucleotide pairspairs

Ionizing radiation Ionizing radiation formation of ions that can react with formation of ions that can react with

nucleotides and the deoxyribose-nucleotides and the deoxyribose-phosphate backbone.phosphate backbone.

Nucleotide excision repairs Nucleotide excision repairs mutationsmutations

MutagenMutagen

UV radiationUV radiation causes causes thymine thymine dimersdimers

Light-repair Light-repair separates separates thymine thymine dimersdimers

MutagenMutagen

Figure 8.20

Spontaneous mutation rate = 1 in Spontaneous mutation rate = 1 in 101099 replicated base pairs or 1 in 10 replicated base pairs or 1 in 1066 replicated genesreplicated genes

Mutagens increase to 10Mutagens increase to 10–5–5 or 10 or 10–3–3 per replicated geneper replicated gene

The Frequency of The Frequency of MutationMutation

SelectionSelection

Positive (direct) selection detects Positive (direct) selection detects mutant cells because they grow or mutant cells because they grow or appear different.appear different.

Negative (indirect) selection detects Negative (indirect) selection detects mutant cells because they do not mutant cells because they do not grow.grow.

Replica PlatingReplica Plating

Figure 8.21

The Ames Test for The Ames Test for Chemical CarcinogensChemical Carcinogens

Figure 8.22

Vertical gene Vertical gene transfertransfer

Horizontal gene Horizontal gene transfertransfer

Genetic Transfer and Genetic Transfer and RecombinationRecombination

•Occurs during Occurs during reproduction, reproduction, between between generations of cellsgenerations of cells•Transfer of genes Transfer of genes between cells of the between cells of the same generationsame generation

TransformationTransformation

Figure 8.24

RecombinationRecombination

Figure 8.25

ConjugationConjugation

Figure 8.27a

ConjugationConjugation

Figure 8.27b

ConjugationConjugation

Figure 8.27c

PlasmidsPlasmids

Figure 8.29

Segments of Segments of DNA that can DNA that can move from move from one region of one region of DNA to DNA to anotheranother

Contain Contain insertion insertion sequences for sequences for cutting and cutting and resealing DNA resealing DNA (transposase)(transposase)

Complex Complex transposons transposons carry other carry other genes genes

TransposonsTransposons

Figure 8.30a, b

Constitutive enzymes are expressed Constitutive enzymes are expressed at a fixed rateat a fixed rate

Other enzymes are expressed only Other enzymes are expressed only as neededas needed Repressible enzymesRepressible enzymes Inducible enzymesInducible enzymes

Regulation of Bacterial Regulation of Bacterial Gene ExpressionGene Expression

RepressionRepression

Figure 8.13

OperonOperon

Figure 8.14.1

Regulation of Gene Regulation of Gene ExpressionExpression

Figure 8.14.2

Regulation of Gene Regulation of Gene ExpressionExpression

Figure 8.14.3

Regulation of Gene Regulation of Gene ExpressionExpression

Figure 8.14.4

Regulation of Gene Regulation of Gene ExpressionExpression

Figure 8.14.5

Regulation of Gene Regulation of Gene ExpressionExpression

Figure 8.15